Engine stalling problem

bigdog · 07-30-2009, 08:43 PM

Here's the latest update....

Spoke with marine mechanic about my engine stalling, backfiring problem
and he thought 'ignition problem'. This is the same marine tech who performed Carb rebuild last July to supposedly correct this issue.
The Carb rebuild was definitely needed, however never really corrected the initial problem.

I personally don't think it's a engine fuel problem, because of the 'back-firing'.
I don't think fuel starvation would cause this type of behavior? A bad fuel pump, would stop fuel delivery, but I don't believe would cause 'back-firing'
Maybe someone can comment on this !

Mechanic said bring boat back to him and he'll work with me to correct.
Now thinking he'll replace Distributor Cap and Rotor. He has had several boats come into shop recently with same symptoms, and after checking
Distributor cap and Rotor, found corrosion in all cases.

I have never replaced same myself, and the second owner. Have had boat
3 seasons, but only put maybe 100 hrs on boat. Not sure when previous owner replaced these parts before or ever ? Could potentially be the culprit for this issue, but bad Coil could also be the problem. Right now it's
basically the process of elimination, starting with the least expensive items first, and working up from there !

'2BlackDogs' suggested checking the ignition wires in darkness and that if the ignit. wires, Coil, etc were arcing this would definitely be obvious, and provide a light-show ! Well, tonight in complete darkness, I mean I couldn't see my hand in front of my face, I started up the engine, and could not see any spark arcing coming from ignition wires, Distributor, or Coil.
Nada, zip, nothing ! If anything was spark/arcing it was not visible.

Will keep Forum informaed about progress. IT WILL BE FIXED !
But my wallet may be empty........

Bigdog

robmac · 07-31-2009, 03:01 AM

BD, even though you didn't see arching you weren't under load, that's why I suggested misting w/water. We do that test all the time because techs work during the day and prefer to eliminate problems rather than empty your wallet.

Winnipesaukee · 07-31-2009, 11:44 AM

Funny, just today I came across a weekend car with similar symptoms. A mechanic I work with said varnish started to form in the fuel lines, AFTER the filter, and backed up the injectors, causing the same problem.

You could be having the same issue, especially now that ethanol is in your gas. Each time you store the boat, the fuel in the line will go bad and varnish. When the boat is started, the varnish before the filter flows into it, clogging it, AND the varnish after the filter goes into the carb where it bottlenecks, killing your engine mid-trip.

Not sure if you have yet, but dump some Seafoam in your gas tank and run the engine. Make sure you have fresh fuel/water filters.

....

A failing head gasket might also cause the same symptoms. You can't compress/burn water efficiently.

bigdog · 07-31-2009, 03:20 PM

Winnipesaukee, FYI I had totally drained my gastank, refilled with fresh 89 Octane gas, new fuel/separting filter, and added a can of Seafom at the recommendation of 'Jst_4_Kiks' (he's a Marine Tech).

Boat ran fine 1st time out this season, second time started this issue again. Engine seems like it's not gettting the gas, with stalling, however with the back-firing
symptoms, it seems to point to an ignition related problem to me. 'Jst_4_Kiks' seems to concur.

Boat at marine repair shop now. Having them check Distributor Cap, Rotor.
Both are probably orginal, at least I have not changed out since I owned boat (3 yrs). Boat is 1995, not sure what original owner did?

Your comments are greatly appreciated !

Bigdog

macshpman · 08-01-2009, 06:04 AM

I had a friend with a boat that his vent line to the fuel tank had become plugged by a insect building his home inside the line. The tank would build a vacuum causing the fuel system to lean out, and stalling backfire would be the signs of the trouble. It would act differently depending on the amount of fuel in the tank and how long and hard he ran the engine. Its worth looking into for sure. He chased this problem for a summer and was changing parts like he was changing his clothes. Very frustrating for him to not be able run 30 miles out from shore to do his fishing and not sure if he was going to be able to make it out and then back in.

bigdog · 08-01-2009, 01:57 PM

Thanks MacShpMan for info about vent hose blockage. I have checked
hose at the top where it eixts the boat, however, have not checked
entire length of hose. Not sure how one would do that, or how to clean out.
Suppose I could run some plastic tubing down through the vent hose to check for obstructions, but then again don't want to force anything down
furhter if something is there....

I can relate to your friend's boat problems. I feel like I'm changing parts like clothes !

Talked to marine tech. this morning, he didn't have a chance to replace Distributor Cap or Rotor Friday because of backlog of customer repairs.
He's going to order parts Monday and work on boat Tuesday. After parts installed he said he'll take to nearby pond to test, best he can do under the conditions. I plan to be on that ride myself !

Marine Tech said it may be Carb problems again, but I reminded him the Carb about the complete Carb rebuild job he did 1 year ago. He said, Carb can still get gummed up with ethanol varnish, even after a short amount of time.

Explained to Marine Tech that I checked for Ignition Wire arching under the cover of darkness last night, and could not detect any arching from wires or Distributor Cap. He came right out and said 'It's not your wires, wires in a boat last forever' ! This seems very contradictory to what has been shared on this Forum. Then again, I'm not the Professional Marine Tech.
Honestly, the collections of knowledge and experience from members of this Forum, have been invalluable !

I find it extremely difficult to believe that the ethanol gas can be constantly causing my issues. Can't just be me ! Everyone would be having problems with their engines. Problem has to be something unrelated to gas.

Let me ask one last question..... If new Distributor Cap and Rotor, do not correct the problem, next replacement part may be the Coil.
Just a process of elimniation at this point....

How can you tell if you have a bad Coil? What are the symptoms?
Would symptoms be contant or intermitant, and it heats up?

Thanks agin.
Bigdog

NoBozo · 08-01-2009, 03:46 PM

Quote:

Originally Posted by bigdog

Thanks MacShpMan for info about vent hose blockage. I have checked
hose at the top where it eixts the boat, however, have not checked
entire length of hose. Not sure how one would do that, or how to clean out.
Suppose I could run some plastic tubing down through the vent hose to check for obstructions, but then again don't want to force anything down
furhter if something is there....

I can relate to your friend's boat problems. I feel like I'm changing parts like clothes !

Talked to marine tech. this morning, he didn't have a chance to replace Distributor Cap or Rotor Friday because of backlog of customer repairs.
He's going to order parts Monday and work on boat Tuesday. After parts installed he said he'll take to nearby pond to test, best he can do under the conditions. I plan to be on that ride myself !

Marine Tech said it may be Carb problems again, but I reminded him the Carb about the complete Carb rebuild job he did 1 year ago. He said, Carb can still get gummed up with ethanol varnish, even after a short amount of time.

Explained to Marine Tech that I checked for Ignition Wire arching under the cover of darkness last night, and could not detect any arching from wires or Distributor Cap. He came right out and said 'It's not your wires, wires in a boat last forever' ! This seems very contradictory to what has been shared on this Forum. Then again, I'm not the Professional Marine Tech.
Honestly, the collections of knowledge and experience from members of this Forum, have been invalluable !

I find it extremely difficult to believe that the ethanol gas can be constantly causing my issues. Can't just be me ! Everyone would be having problems with their engines. Problem has to be something unrelated to gas.

Let me ask one last question..... If new Distributor Cap and Rotor, do not correct the problem, next replacement part may be the Coil.
Just a process of elimniation at this point....

How can you tell if you have a bad Coil? What are the symptoms?
Would symptoms be contant or intermitant, and it heats up?

Thanks agin.
Bigdog

Spark plug wires WILL deteriorate over time. Ten years of living inside that engine box with the heat will dry out the plug wire insulation and allow arcing...even if you cannot see it at night. Backfiring is likely an ignition problem. My educated guess is the distributer cap. Two screws loosened will allow it to be removed....without disconnecting the wires. Look inside the cap at the terminals around the inside rim. If the terminals look "Crusty", they can be scraped clean with a knife or screwdriver blade. The outside tip of the rotor can may also look crusty. Scrape them clean and you're back in business. Buy a new cap when you can scrape up the $45-50. I prefer Mercruiser parts rather than Sierra, even though Sierra is probably Half the cost.

Another possabity: If someone has been in the engine room, it's possable one of the spark plug wires came loose from a spark plug inadvertantly by being bumped into. I once actually had a spark plug wire dislodge itself from the plug during a backfire. At that time I was having plug wire crosstalking problems and at night, it looked like a christmas tree in the dark. If one leaky plug wire comes in contact with another leaky plug wire this will cause all manner of backfiring and rough running.

An ignition coil rarely fails, but when it does it usually happens when the coil gets hot and shorts out internally. When the coil is cold it may work fine.

BTW: A distributer cap for a boat with an inboard engine MUST BE Marine Certified. Automotive distributer caps are NOT acceptible.

bigdog · 08-01-2009, 06:57 PM

Thanks NoBozo for the info.

I have to agree with you about the Ignition wires ! I have replaced in the 3 yrs I've owned the boat, and don't know when previous owner replaced, or if wire are original?

The stalling and backfiring only starts after running boat for about 15minutes. When I initially start the boat it appears to run smooth, even under acceleration. Doesn't seem to be an issue.

If the Distributor Cap and/or Rotor had corrosion wouldn't the stalling, running rough and back-firing behavior begin as soon as the engine was started ? Cap & Rotor being replaced next week with new parts. Not going to bother attempting to clean, as parts may be original ?

Also, I've been reading that the fuel pump (electric MerCruiser in my case),
can have problems with an internal diaphragm, causing improper flow and pressure of gas to the Carb. Under these circumstances the Carb would run 'lean'. I have been told when Carb runs lean and can cause 'back-fire' !

So we still have several possible issues causing the problem.

Trying to take a one step approach, with the least costly first.
Will let Forum know results.

Oh...... I'll be on Winnie all next week, 8/8, with family and boat.
If I need to get additional parts over vacation, I have heard of M & M Salvage in Meredith. I realize all their parts are used.
Has anyone purchased from these folks ? Comments?

Thanks,
Bigdog

macshpman · 08-01-2009, 08:05 PM

If the vent is clear I would lean towards electrical. Coil could be the problem. I would lean more towards that then the cap, rotor, wires or sparkplugs. They would tend to act up all the time and not just now and then. I myself would change the pick up in the distributor first. Dont let the mechanic tell you that they are either good or bad. I personal have seen them work fine untill they get hot and then stop working. Once cold again it will work. I believe mercruiser has an update pickup because of this problem. Good luck

dan · 08-01-2009, 10:16 PM

Cold engine should be on full choke. Rich mixture. Engine warms up, choke opens, mixture leans out. Vac. leak somewhere causing lean backfire and or stalling?

Jersey Joe · 08-02-2009, 06:45 AM

Had the boat out last weekend for first time this year - I had replaced the coil, the fuel lines and the "anit-siphon valve". I ran for about 2 hours without stallling. I hope it is fixed, but last time out it took longer than that to exhibit the problem. Headed up to the big lake this weekend so I purchased Sea Tow insurance just in case and hope for the best.

NoBozo · 08-02-2009, 10:02 AM

There is one more thing relative to the distributor cap that I forgot to mention. Moisture. Moisture inside the cap will be evident by condensed droplets of water inside the cap when the engine is cold. The engine may run OK untill up to temperature, at which time the moisture wants to evaporate and turns into water vapor. Water vapor (fog) inside the cap is not conducive to smooth running. Perhaps if you have "hosed down" the engine recently, or got the distributer wet somehow, this might have introduced some moisture.

BTW: Looking for spark plug wires Arcing under the hood at night is always easiest to spot when it's foggy or hazy.....moisture.

My experience has been....the problem is almost Never as serious as it might seem. You are on the right track by looking at the least expensive solution because that is usually the correct one.

bigdog · 08-03-2009, 08:47 PM

Well tomorrow I should know if my engine stalling, backfiring problem has been resolved. with the latest replacements of Distributor Cap & Rotor.
(Hope marine techs thought to replace 'Pickup Wheel' in the Distributor?).
All to be installed tomorrow, then a in-water test with marine techs. At least that's the plan....

If this does not correct the stalling and backfiring, then I guess I have to look deeper to the root cause???

Again, the engine runs smoothly for about 10 minutes. After the engine stalls and backfires, I can almost always start up right away, and run at wake speed, but that's all..... As soon as I begin to increase throttle, stalls again.

After talking to a multitude of people about my engine problem, both here in this Forum and others friends, the following suggestions have been given as the possible issue. Came up with a list of 12 possible problems,
not necessarily in any particular order.

Gentlemen... Place your bets on your number !

1. Ignition module
2. Ignition wires - broken inside insulation and shorting out
3. Coil bad
4. Ignition Timing not set properly - Late timing
5. Electric fuel pump-faulty pressure loss
6. Water in fuel causing lean fuel condition
7. Carb Accelerator pump sticking
8, Choke open or sticking
9. Anti-syphon valve clogged
10. Firing order - Plugs not connected correctly to Distributor
11. Carb jets clogged
12. Bad Valve

SIKSUKR · 08-03-2009, 10:05 PM

I would definately look at the fuel tank vent.This has a sign of a fuel tank not being able to vent. I would rule that out by disconnecting the fuel vent line temporarily while running under similar conditions that you have already done.This is a test that costs nothing.If the valve has failed and wont let the tank vent,It's like sucking out of a bottle.

ITD · 08-04-2009, 07:40 AM

Quote:

Originally Posted by SIKSUKR

I would definately look at the fuel tank vent.This has a sign of a fuel tank not being able to vent. I would rule that out by disconnecting the fuel vent line temporarily while running under similar conditions that you have already done.This is a test that costs nothing.If the valve has failed and wont let the tank vent,It's like sucking out of a bottle.

Easiest way to test for this problem is to crack open the gas cap when the boat starts stalling. If the boat restarts you've found the cause.

LIforrelaxin · 08-04-2009, 09:57 AM

Running a boat out of the water is not a good why to test how it is running especially if it a through hub exhaust..... by running it out of the water you take the back preasure of the engine exhaust system.... running on muffs is good if you are trying to start the boat for the first time in a while or, winterizing, and hey evening if you just but some new plugs in, but it is not a substition for running it in the water....

6meter · 08-04-2009, 10:32 AM

I have read this whole thread and sounds just like my fathers and my boat. Dads boat is gone so I can't check it but my solution was the coil. Run for a while then backfire with no power above idle. Would start right up if stalled.

NoBozo · 08-04-2009, 07:05 PM

Quote:

Originally Posted by bigdog

Well tomorrow I should know if my engine stalling, backfiring problem has been resolved. with the latest replacements of Distributor Cap & Rotor.
(Hope marine techs thought to replace 'Pickup Wheel' in the Distributor?).
All to be installed tomorrow, then a in-water test with marine techs. At least that's the plan....

If this does not correct the stalling and backfiring, then I guess I have to look deeper to the root cause???

Again, the engine runs smoothly for about 10 minutes. After the engine stalls and backfires, I can almost always start up right away, and run at wake speed, but that's all..... As soon as I begin to increase throttle, stalls again.

After talking to a multitude of people about my engine problem, both here in this Forum and others friends, the following suggestions have been given as the possible issue. Came up with a list of 12 possible problems,
not necessarily in any particular order.

Gentlemen... Place your bets on your number !

1. Ignition module
2. Ignition wires - broken inside insulation and shorting out
3. Coil bad
4. Ignition Timing not set properly - Late timing
5. Electric fuel pump-faulty pressure loss
6. Water in fuel causing lean fuel condition
7. Carb Accelerator pump sticking
8, Choke open or sticking
9. Anti-syphon valve clogged
10. Firing order - Plugs not connected correctly to Distributor
11. Carb jets clogged
12. Bad Valve

------------------------------------------------------------------
1. Ignition module.....??

2. Ignition wires - broken inside insulation and shorting out. Spark Plug Wires?? They are now new...YES?

3. Coil bad. MAYBE

4. Ignition Timing not set properly - Late timing. Timing does NOT CHANGE by itself. Timing once set is good for the life of the engine. Period. The timing is adjusted by "twisting" the distributer one way or the other and then tightening it back up. CHECK IT: Grab a hold of the distributer with both hands and try to twist it. IF it turns..then your timing is OFF because the clamp down screw is loose. If it's loose..come back here and ask how to fix it.

5. Electric fuel pump-faulty pressure loss. DO You KNOW that you HAVE an Electric fuel pump..??..or did someone just TELL you..?? My 5.7 Mercruiser V8 (1986) has a mechanical pump.

6. Water in fuel causing lean fuel condition. Water does NOT LEAN the mixture. It will just "WET" the spark plugs and stop the engine.

7. Carb Accelerator pump sticking. This only comes in to play when you GAS IT....pedal to the metal...

8, Choke open or sticking. Choke is supposed to be open when the engine is warm. It's automatic. Take off the "flame arrester" (looks like an air filter) and look at the choke..when it's COLD, .......and after it warm. It looks like a little door that is shut when cold. Good. When it warms up..the little door should be fully open. GOOD.

9. Anti-syphon valve clogged. In all my years (I'm 67) working on engines: I have NO IDEA what an Anti Syphon Valve is.

10. Firing order - Plugs not connected correctly to Distributor. If the engine runs at all.....this is unlikely. If Two plugs are miswired..switched..the engine will NEVER run smoothly.

11. Carb jets clogged. This IS Possable..ETHONAL.

12. Bad Valve. What valve? NOT Likely

BIGDOG: Cheer up..You are getting close to the solution.

Jersey Joe · 08-05-2009, 10:27 AM

Nobozo

I did not know about the Anti-Siphon valve either, until a mechanic told me to check it.

Apparently, what it does is prevents the tank from emptying inside your hull if you should develop a leak (at least what he told me). It is a 1 - way valve from the tank to the vent. If fuel runs out of the tank too fast, the valve will close and create a vacum in the tank. Mine was all crudded up with an off white crusty buildup, probably from ethanol.

The Mechanic I was working with told me that this would make sense for my problem - because the boat will run fine at idle, but when you push the throttle down, once you burn off the fuel in the carb, you can't pump enough fuel back into the carb to keep it running above an idle becuase the valve creates a vacum lock in the tank. In my instance, if you let the boat sit for a half hour - it will run fine again - which would make sense as air gets back into the tank to break the vacum.

I am no expert - just adding what limited knowledge I have to help a fellow boater.

Hey BigDog - I carry a wrench that fits my drainplug on the boat at all times, much easier and quieter than the C-4

6meter · 08-05-2009, 03:50 PM

Nobozo, I would say that you're right on. But I'll add a thought on a couple of things on the list. The firing order should be right, the problem was there before the plugs were changed. Will the ethanhol eat the diaphram in a mechanical fuel pump? I believe Bigdog's boat is a '96 so it could have an electric fuel pump. I borrowed my brothers coil to try 2 years ago. It fixed it. Ran great last year. Dies out this year. So there is interest in this topic for me. I'll admit the same about an anti siphon valve. Did they use them in '86? A distributor module will act just like running out of gas. Will stay tuned.

NoBozo · 08-05-2009, 03:58 PM

Quote:

Originally Posted by Jersey Joe

Nobozo

I did not know about the Anti-Siphon valve either, until a mechanic told me to check it.

Apparently, what it does is prevents the tank from emptying inside your hull if you should develop a leak (at least what he told me). It is a 1 - way valve from the tank to the vent. If fuel runs out of the tank too fast, the valve will close and create a vacum in the tank. Mine was all crudded up with an off white crusty buildup, probably from ethanol.

The Mechanic I was working with told me that this would make sense for my problem - because the boat will run fine at idle, but when you push the throttle down, once you burn off the fuel in the carb, you can't pump enough fuel back into the carb to keep it running above an idle becuase the valve creates a vacum lock in the tank. In my instance, if you let the boat sit for a half hour - it will run fine again - which would make sense as air gets back into the tank to break the vacum.

I am no expert - just adding what limited knowledge I have to help a fellow boater.

Hey BigDog - I carry a wrench that fits my drainplug on the boat at all times, much easier and quieter than the C-4

------------------------------------------------------------
Thanks Joe for your response. It got me to thinking and got me off my butt to do some Googling and here is what I found that makes sense to me:

Question: My fuel tank is higher than my engine. Do I need an anti-siphon valve? There is a small round valve installed just above the tank where the fuel line leaves the tank. Could this be some sort of anti-siphon valve?

Answer: The valve to which you are referring is probably a small spring-loaded one-way check valve. The spring-loading on the valve is sufficient to prevent fuel from passing through it statically through a siphon (usually no more than 2 or 3 psi), but low enough so that the fuel pump can pull fuel through its mechanism while the engine is running.

These check valves will sometimes create a problem with electric pumps, since they (electric pumps) are less forgiving of even slight increases in suction head than are mechanical pumps.

If there is a wire connected to the valve on your boat, it is probably an electric solenoid valve that spring-loads closed whenever the ignition switch is turned off, and power is removed from the valve. These valves have the advantage of adding virtually no head loss to the suction side of the fuel pump, but they are vulnerable to malfunction, since they rely on electrical energy to hold them open.

It is not at all clear to us that either of these valves is actually required by the Coast Guard. In our experience, most people rely on a manual valve to prevent fuel from passing from their fuel tanks when the boat is left unattended. - Updated: January 5, 2004
-------------------------------------------------------
My take (NB): In Short; This valve is a TWO STAGE valve allowing gas to be Sucked through it by the fuel pump, but will NOT allow fuel to "Siphon" out "on it's own".

Thanks again Joe for a teachable moment. I learn something new every day.

bigdog · 08-05-2009, 07:57 PM

Jersey Joe,
Your explanation describes my engine symptoms exactly ! However the marine tech said he checked the A.S.V today and it appears to be working as it should and is not obstructed. I did not examine myslef, so I cannot confirm.

Also love your comment and humor about keeping a wrench that fits my drainplug, rather than my C-4 alternative ! What can I say, I like things that go BANG !

NoBozo,
Your discertation about the A.S.V. was very accurately described perfectly !
Thanks for educating the rest of us who may not understand how this part functions.

07-30-2009, 08:43 PM	#1
bigdog Senior Member Join Date: Apr 2006 Location: Central MA-Gilford Posts: 1,447 Thanks: 342 Thanked 119 Times in 96 Posts	Engine Stalling Problem continued Here's the latest update.... Spoke with marine mechanic about my engine stalling, backfiring problem and he thought 'ignition problem'. This is the same marine tech who performed Carb rebuild last July to supposedly correct this issue. The Carb rebuild was definitely needed, however never really corrected the initial problem. I personally don't think it's a engine fuel problem, because of the 'back-firing'. I don't think fuel starvation would cause this type of behavior? A bad fuel pump, would stop fuel delivery, but I don't believe would cause 'back-firing' Maybe someone can comment on this ! Mechanic said bring boat back to him and he'll work with me to correct. Now thinking he'll replace Distributor Cap and Rotor. He has had several boats come into shop recently with same symptoms, and after checking Distributor cap and Rotor, found corrosion in all cases. I have never replaced same myself, and the second owner. Have had boat 3 seasons, but only put maybe 100 hrs on boat. Not sure when previous owner replaced these parts before or ever ? Could potentially be the culprit for this issue, but bad Coil could also be the problem. Right now it's basically the process of elimination, starting with the least expensive items first, and working up from there ! '2BlackDogs' suggested checking the ignition wires in darkness and that if the ignit. wires, Coil, etc were arcing this would definitely be obvious, and provide a light-show ! Well, tonight in complete darkness, I mean I couldn't see my hand in front of my face, I started up the engine, and could not see any spark arcing coming from ignition wires, Distributor, or Coil. Nada, zip, nothing ! If anything was spark/arcing it was not visible. Will keep Forum informaed about progress. IT WILL BE FIXED ! But my wallet may be empty........ Bigdog

07-31-2009, 11:44 AM	#3
Winnipesaukee Senior Member Join Date: Feb 2007 Posts: 233 Thanks: 14 Thanked 16 Times in 12 Posts	Funny, just today I came across a weekend car with similar symptoms. A mechanic I work with said varnish started to form in the fuel lines, AFTER the filter, and backed up the injectors, causing the same problem. You could be having the same issue, especially now that ethanol is in your gas. Each time you store the boat, the fuel in the line will go bad and varnish. When the boat is started, the varnish before the filter flows into it, clogging it, AND the varnish after the filter goes into the carb where it bottlenecks, killing your engine mid-trip. Not sure if you have yet, but dump some Seafoam in your gas tank and run the engine. Make sure you have fresh fuel/water filters. .... A failing head gasket might also cause the same symptoms. You can't compress/burn water efficiently. __________________ Sail fast, live slow!

07-31-2009, 03:20 PM	#4
bigdog Senior Member Join Date: Apr 2006 Location: Central MA-Gilford Posts: 1,447 Thanks: 342 Thanked 119 Times in 96 Posts	Engine stalling problem Winnipesaukee, FYI I had totally drained my gastank, refilled with fresh 89 Octane gas, new fuel/separting filter, and added a can of Seafom at the recommendation of 'Jst_4_Kiks' (he's a Marine Tech). Boat ran fine 1st time out this season, second time started this issue again. Engine seems like it's not gettting the gas, with stalling, however with the back-firing symptoms, it seems to point to an ignition related problem to me. 'Jst_4_Kiks' seems to concur. Boat at marine repair shop now. Having them check Distributor Cap, Rotor. Both are probably orginal, at least I have not changed out since I owned boat (3 yrs). Boat is 1995, not sure what original owner did? Your comments are greatly appreciated ! Bigdog

08-01-2009, 06:04 AM	#5
macshpman Member Join Date: May 2007 Location: Southern NH Posts: 32 Thanks: 3 Thanked 0 Times in 0 Posts	Similar Problem I had a friend with a boat that his vent line to the fuel tank had become plugged by a insect building his home inside the line. The tank would build a vacuum causing the fuel system to lean out, and stalling backfire would be the signs of the trouble. It would act differently depending on the amount of fuel in the tank and how long and hard he ran the engine. Its worth looking into for sure. He chased this problem for a summer and was changing parts like he was changing his clothes. Very frustrating for him to not be able run 30 miles out from shore to do his fishing and not sure if he was going to be able to make it out and then back in. __________________ Just remember Your DEAD alot longer then your ALIVE! Enjoy every DAY

08-01-2009, 01:57 PM	#6
bigdog Senior Member Join Date: Apr 2006 Location: Central MA-Gilford Posts: 1,447 Thanks: 342 Thanked 119 Times in 96 Posts	Engine Stalling Problems Thanks MacShpMan for info about vent hose blockage. I have checked hose at the top where it eixts the boat, however, have not checked entire length of hose. Not sure how one would do that, or how to clean out. Suppose I could run some plastic tubing down through the vent hose to check for obstructions, but then again don't want to force anything down furhter if something is there.... I can relate to your friend's boat problems. I feel like I'm changing parts like clothes ! Talked to marine tech. this morning, he didn't have a chance to replace Distributor Cap or Rotor Friday because of backlog of customer repairs. He's going to order parts Monday and work on boat Tuesday. After parts installed he said he'll take to nearby pond to test, best he can do under the conditions. I plan to be on that ride myself ! Marine Tech said it may be Carb problems again, but I reminded him the Carb about the complete Carb rebuild job he did 1 year ago. He said, Carb can still get gummed up with ethanol varnish, even after a short amount of time. Explained to Marine Tech that I checked for Ignition Wire arching under the cover of darkness last night, and could not detect any arching from wires or Distributor Cap. He came right out and said 'It's not your wires, wires in a boat last forever' ! This seems very contradictory to what has been shared on this Forum. Then again, I'm not the Professional Marine Tech. Honestly, the collections of knowledge and experience from members of this Forum, have been invalluable ! I find it extremely difficult to believe that the ethanol gas can be constantly causing my issues. Can't just be me ! Everyone would be having problems with their engines. Problem has to be something unrelated to gas. Let me ask one last question..... If new Distributor Cap and Rotor, do not correct the problem, next replacement part may be the Coil. Just a process of elimniation at this point.... How can you tell if you have a bad Coil? What are the symptoms? Would symptoms be contant or intermitant, and it heats up? Thanks agin. Bigdog

07-31-2009, 03:01 AM	#2
robmac Senior Member Join Date: Jan 2005 Location: Nashua,Meredith Posts: 951 Thanks: 213 Thanked 106 Times in 81 Posts	BD, even though you didn't see arching you weren't under load, that's why I suggested misting w/water. We do that test all the time because techs work during the day and prefer to eliminate problems rather than empty your wallet.

08-01-2009, 06:57 PM	#8
bigdog Senior Member Join Date: Apr 2006 Location: Central MA-Gilford Posts: 1,447 Thanks: 342 Thanked 119 Times in 96 Posts	Engine Stalling Problem Thanks NoBozo for the info. I have to agree with you about the Ignition wires ! I have replaced in the 3 yrs I've owned the boat, and don't know when previous owner replaced, or if wire are original? The stalling and backfiring only starts after running boat for about 15minutes. When I initially start the boat it appears to run smooth, even under acceleration. Doesn't seem to be an issue. If the Distributor Cap and/or Rotor had corrosion wouldn't the stalling, running rough and back-firing behavior begin as soon as the engine was started ? Cap & Rotor being replaced next week with new parts. Not going to bother attempting to clean, as parts may be original ? Also, I've been reading that the fuel pump (electric MerCruiser in my case), can have problems with an internal diaphragm, causing improper flow and pressure of gas to the Carb. Under these circumstances the Carb would run 'lean'. I have been told when Carb runs lean and can cause 'back-fire' ! So we still have several possible issues causing the problem. Trying to take a one step approach, with the least costly first. Will let Forum know results. Oh...... I'll be on Winnie all next week, 8/8, with family and boat. If I need to get additional parts over vacation, I have heard of M & M Salvage in Meredith. I realize all their parts are used. Has anyone purchased from these folks ? Comments? Thanks, Bigdog

08-01-2009, 08:05 PM	#9
macshpman Member Join Date: May 2007 Location: Southern NH Posts: 32 Thanks: 3 Thanked 0 Times in 0 Posts	2nd thought If the vent is clear I would lean towards electrical. Coil could be the problem. I would lean more towards that then the cap, rotor, wires or sparkplugs. They would tend to act up all the time and not just now and then. I myself would change the pick up in the distributor first. Dont let the mechanic tell you that they are either good or bad. I personal have seen them work fine untill they get hot and then stop working. Once cold again it will work. I believe mercruiser has an update pickup because of this problem. Good luck __________________ Just remember Your DEAD alot longer then your ALIVE! Enjoy every DAY

08-01-2009, 10:16 PM	#10
dan Member Join Date: Jan 2005 Location: moultonborough/billerica Posts: 42 Thanks: 21 Thanked 7 Times in 4 Posts	I have been told when Carb runs lean and can cause 'back-fire' ! Cold engine should be on full choke. Rich mixture. Engine warms up, choke opens, mixture leans out. Vac. leak somewhere causing lean backfire and or stalling?

08-02-2009, 06:45 AM	#11
Jersey Joe Member Join Date: Aug 2005 Posts: 28 Thanks: 0 Thanked 0 Times in 0 Posts	Had the boat out last weekend for first time this year - I had replaced the coil, the fuel lines and the "anit-siphon valve". I ran for about 2 hours without stallling. I hope it is fixed, but last time out it took longer than that to exhibit the problem. Headed up to the big lake this weekend so I purchased Sea Tow insurance just in case and hope for the best.

08-02-2009, 10:02 AM	#12
NoBozo Senior Member Join Date: Jun 2008 Location: Portsmouth. RI Posts: 2,231 Thanks: 400 Thanked 460 Times in 308 Posts	More On Distributer Cap There is one more thing relative to the distributor cap that I forgot to mention. Moisture. Moisture inside the cap will be evident by condensed droplets of water inside the cap when the engine is cold. The engine may run OK untill up to temperature, at which time the moisture wants to evaporate and turns into water vapor. Water vapor (fog) inside the cap is not conducive to smooth running. Perhaps if you have "hosed down" the engine recently, or got the distributer wet somehow, this might have introduced some moisture. BTW: Looking for spark plug wires Arcing under the hood at night is always easiest to spot when it's foggy or hazy.....moisture. My experience has been....the problem is almost Never as serious as it might seem. You are on the right track by looking at the least expensive solution because that is usually the correct one.

08-03-2009, 08:47 PM	#13
bigdog Senior Member Join Date: Apr 2006 Location: Central MA-Gilford Posts: 1,447 Thanks: 342 Thanked 119 Times in 96 Posts	Engine stalling problem Well tomorrow I should know if my engine stalling, backfiring problem has been resolved. with the latest replacements of Distributor Cap & Rotor. (Hope marine techs thought to replace 'Pickup Wheel' in the Distributor?). All to be installed tomorrow, then a in-water test with marine techs. At least that's the plan.... If this does not correct the stalling and backfiring, then I guess I have to look deeper to the root cause??? Again, the engine runs smoothly for about 10 minutes. After the engine stalls and backfires, I can almost always start up right away, and run at wake speed, but that's all..... As soon as I begin to increase throttle, stalls again. After talking to a multitude of people about my engine problem, both here in this Forum and others friends, the following suggestions have been given as the possible issue. Came up with a list of 12 possible problems, not necessarily in any particular order. Gentlemen... Place your bets on your number ! 1. Ignition module 2. Ignition wires - broken inside insulation and shorting out 3. Coil bad 4. Ignition Timing not set properly - Late timing 5. Electric fuel pump-faulty pressure loss 6. Water in fuel causing lean fuel condition 7. Carb Accelerator pump sticking 8, Choke open or sticking 9. Anti-syphon valve clogged 10. Firing order - Plugs not connected correctly to Distributor 11. Carb jets clogged 12. Bad Valve Last edited by bigdog; 08-03-2009 at 08:49 PM. Reason: spelling

08-03-2009, 10:05 PM	#14
SIKSUKR Senior Member Join Date: Apr 2004 Posts: 5,075 Thanks: 215 Thanked 903 Times in 509 Posts	something else to try after your new parts I would definately look at the fuel tank vent.This has a sign of a fuel tank not being able to vent. I would rule that out by disconnecting the fuel vent line temporarily while running under similar conditions that you have already done.This is a test that costs nothing.If the valve has failed and wont let the tank vent,It's like sucking out of a bottle. __________________ SIKSUKR

The Following User Says Thank You to ITD For This Useful Post:
bigdog (08-04-2009)

08-04-2009, 09:57 AM	#16
LIforrelaxin Senior Member Join Date: May 2006 Location: Texas, Lake Ray Hubbard and NH, Long Island Winnipesaukee Posts: 2,871 Thanks: 1,037 Thanked 892 Times in 524 Posts	something I haven't seen stated Running a boat out of the water is not a good why to test how it is running especially if it a through hub exhaust..... by running it out of the water you take the back preasure of the engine exhaust system.... running on muffs is good if you are trying to start the boat for the first time in a while or, winterizing, and hey evening if you just but some new plugs in, but it is not a substition for running it in the water.... __________________ Life is about how much time you can spend relaxing... I do it on an island that isn't really an island.....

08-04-2009, 10:32 AM	#17
6meter Member Join Date: Jul 2009 Posts: 27 Thanks: 2 Thanked 2 Times in 2 Posts	my vote #3 I have read this whole thread and sounds just like my fathers and my boat. Dads boat is gone so I can't check it but my solution was the coil. Run for a while then backfire with no power above idle. Would start right up if stalled.

08-05-2009, 10:27 AM	#19
Jersey Joe Member Join Date: Aug 2005 Posts: 28 Thanks: 0 Thanked 0 Times in 0 Posts	Nobozo I did not know about the Anti-Siphon valve either, until a mechanic told me to check it. Apparently, what it does is prevents the tank from emptying inside your hull if you should develop a leak (at least what he told me). It is a 1 - way valve from the tank to the vent. If fuel runs out of the tank too fast, the valve will close and create a vacum in the tank. Mine was all crudded up with an off white crusty buildup, probably from ethanol. The Mechanic I was working with told me that this would make sense for my problem - because the boat will run fine at idle, but when you push the throttle down, once you burn off the fuel in the carb, you can't pump enough fuel back into the carb to keep it running above an idle becuase the valve creates a vacum lock in the tank. In my instance, if you let the boat sit for a half hour - it will run fine again - which would make sense as air gets back into the tank to break the vacum. I am no expert - just adding what limited knowledge I have to help a fellow boater. Hey BigDog - I carry a wrench that fits my drainplug on the boat at all times, much easier and quieter than the C-4

08-05-2009, 03:50 PM	#20
6meter Member Join Date: Jul 2009 Posts: 27 Thanks: 2 Thanked 2 Times in 2 Posts	Nobozo, I would say that you're right on. But I'll add a thought on a couple of things on the list. The firing order should be right, the problem was there before the plugs were changed. Will the ethanhol eat the diaphram in a mechanical fuel pump? I believe Bigdog's boat is a '96 so it could have an electric fuel pump. I borrowed my brothers coil to try 2 years ago. It fixed it. Ran great last year. Dies out this year. So there is interest in this topic for me. I'll admit the same about an anti siphon valve. Did they use them in '86? A distributor module will act just like running out of gas. Will stay tuned.

08-05-2009, 07:57 PM	#22
bigdog Senior Member Join Date: Apr 2006 Location: Central MA-Gilford Posts: 1,447 Thanks: 342 Thanked 119 Times in 96 Posts	Engine Stalling Jersey Joe, Your explanation describes my engine symptoms exactly ! However the marine tech said he checked the A.S.V today and it appears to be working as it should and is not obstructed. I did not examine myslef, so I cannot confirm. Also love your comment and humor about keeping a wrench that fits my drainplug, rather than my C-4 alternative ! What can I say, I like things that go BANG ! NoBozo, Your discertation about the A.S.V. was very accurately described perfectly ! Thanks for educating the rest of us who may not understand how this part functions.