Outboard Compression

Denny Crane · 09-09-2019, 04:47 PM

After purchasing a pontoon boat a few years ago for the lake I am thinking of getting my 22' back on the water for a few salt water trips each year, nothing hard core. It has a 1985 evinrude 175 hp vro 2 stroke. New gas, plugs, etc, has spark and almost fires up. When I did a compression test each cylinder was 61 psi. When I first got the boat 10 years ago compression was 89 each but I was told evinrude runs a little lower than others. My question is before I get into cleaning and rebuilding carburetors can anyone tell me whether I should bother or not, given the compression numbers. I don't know the ranges of good/bad compression and whether I should just shop for another older engine. While I love my newer Mercury 4 stroke on my pontoon, I like to tinker and don't know when to call it quits sometimes. I doubt a shop will work on something this old. Thank you!

Descant · 09-09-2019, 10:47 PM

Some older, more experienced mechanics ("technicians") love the opportunity to work on older engines. e don't all ahve confience in additives, but if a little STP improves the compression, that might give a sense of direction. Why did the numbers drop if the engine hasn't been used for several years?
Most professional mechanics disavow the value of ethetr (Starting fluid, weasel piss in my day) but it may help to fire he engine and burn ot wateber old gas is in the system until you can get fresh gas flowing,. with some anti E-10 stabilizer. Your engine may need to be re-tuned to compensate for E-10. I don't know. just free lancing my old time thoughts. It used to be simple: air, fuel, ignition. Now it's air, mixed fuel, ignition, electronics. "There's an app for that."

ApS · 09-10-2019, 03:11 AM

Add some Marvel Mystery Oil directly into the cylinders, let it soak a few days, use starter fluid to keep it running or stuttering a few minutes, and retest compression when cold. (Or warm like before). Use the same gauge, then retest with another. Your former 89 is OK for a 2-stroke.

A substitute for MMO is automatic transmission fluid, but it's missing the minty odor.

8gv · 09-10-2019, 06:56 AM

I have yet to try this product but it was recommended to me by a tech on the Mercury service phone line.

He said it can make a big difference.

Mercury/quicksilver W Power Tune At 12 92-858080q03 https://www.amazon.com/dp/B00BO88QIK..._m74DDbJM3SAYZ

Dave R · 09-13-2019, 11:54 AM

The odds of all the cylinders having the the same low compression are really slim and it may just be a problem with the gauge or test technique. Normally, as the engine wears, you'd expect the range between cylinders to increase.

Did you open the throttle for the test? A closed throttle would likely make all the cylinders read low, especially on a two stroke where you are counting on the air rushing in to spread the oil/fuel mix around and lube the rings.

I would spend the time and money to get it running then see how it works. If the compression is really low, it may be due to stuck rings and it might improve after you flog it a bit under load.

8gv · 09-13-2019, 06:12 PM

Quote:

Originally Posted by Dave R

Did you open the throttle for the test? A closed throttle would likely make all the cylinders read low, especially on a two stroke where you are counting on the air rushing in to spread the oil/fuel mix around and lube the rings.

This is a common mistake!

Good point.

Cal Coon · 09-21-2019, 08:21 PM

I have heard that Yamaha ring free is really good stuff. Can't hurt to try, and I would also put some good old fashioned Marvel Mystery oil in them cylinders. That stuff can work miracles sometimes...

Cal Coon · 09-23-2019, 05:16 PM

Quote:

Originally Posted by Top-Water

The secret is letting it sit for a few days. It's illegal in 49 sates.

Good luck.

Part 1 https://www.youtube.com/watch?v=HvHLHfdAZbI

Part 2 https://www.youtube.com/watch?v=6wLjh24VqPI

How can it be illegal if it's readily available to buy over the counter at just about any retail store? I did a little research and found that a couple of it's ingredients are supposedly banned in the US, but again, how come it's for sale any where you go...?? Seems kind of strange. Illegal or not, it's good stuff, and I wouldn't hesitate to use it for a second. Maybe it's going to be another one of those products you need to go out and buy a lifetime of inventory on before they stop selling it altogether like incandescent light bulbs and plastic straws... lol

Cal Coon · 09-24-2019, 06:24 PM

Quote:

Originally Posted by Top-Water

You took that way to seriously.

I figured you would ask what state was it legal in to use, then I would have to kill you.

Yeah, you got me...!!! That's why I did the research! I thought it being illegal was a bit ridiculous, but, to my surprise, I found that there is a couple ingredients in it that actually are banned in the US, that's why I thought you were serious... Good one. lol

8gv · 09-24-2019, 06:36 PM

Quote:

Originally Posted by Cal Coon

Yeah, you got me...!!! That's why I did the research! I thought it being illegal was a bit ridiculous, but, to my surprise, I found that there is a couple ingredients in it that actually are banned in the US, that's why I thought you were serious... Good one. lol

Those ingredients give MMO its unique flavor.

Denny Crane · 09-30-2019, 01:17 PM

Thanks for all your help with a motor that was destined for a salvage yard. I bought carb kits for 3 double carburetors, dismantled them, soaked them in a gallon cleaner kit from Advanced Auto, put it all back together having help from pics I took. I changed the primer solonoid and I used fresh gas and evinrude 2 stroke oil. For the first time since I owned this boat it started on the first turn of the key. I didn't have time to do another compression test but I will.
However, once it started after using the primer bulb, it would stall after running for a minute. I would prime, start, run til it stalled continuously. Next questions or advice: Should I change the vro pump which mixes the fuel and oil? It's not a cheap part but i don't know if there is anything else I should troubleshoot or test first. it has all new fuel lines and fuel filter.
Thanks again

Dave R · 09-30-2019, 04:09 PM

Quote:

Originally Posted by Denny Crane

Thanks for all your help with a motor that was destined for a salvage yard. I bought carb kits for 3 double carburetors, dismantled them, soaked them in a gallon cleaner kit from Advanced Auto, put it all back together having help from pics I took. I changed the primer solonoid and I used fresh gas and evinrude 2 stroke oil. For the first time since I owned this boat it started on the first turn of the key. I didn't have time to do another compression test but I will.
However, once it started after using the primer bulb, it would stall after running for a minute. I would prime, start, run til it stalled continuously. Next questions or advice: Should I change the vro pump which mixes the fuel and oil? It's not a cheap part but i don't know if there is anything else I should troubleshoot or test first. it has all new fuel lines and fuel filter.
Thanks again

I suspect the VRO/Fuel pump might be bad based on your description, BUT low compression on the cylinder that provides the pulses to operate the pump may be the real problem. Check compression again very carefully before spending any money on the pump.

Good info on VRO here: http://continuouswave.com/whaler/reference/VRO.html

Denny Crane · 10-01-2019, 09:48 PM

Next round! My engine started beautifully and kept running this time, however gas kept pouring out of the hole in the top hole front face between the 2 carburetors, mostly the top carburator. The primer hose goes into the top of each carberator. I did change the primer solenoid parts, not the whole solenoid. The gas kept flowing down the front face.
I checked the compression again after it ran, full throttle, and each cylinder was once again 60psi. I will admit the compression kit is from harbor freight.
I may be at my limit here, but I'm close.
Sorry the pic is upside down.

Dave R · 10-02-2019, 05:41 AM

I do not understand where the gas was pouring from based on your description, but it sure sounds like nothing more than a sticking float in the carburetor that was dumping fuel. If I am right, the bowl probably has some ethanol-caused crud in it. I would clean all the carbs if it were my engine. I don;t know of any additives that will dissolve the crud, sad to say. I imagine youtube would be a great resource for instructions about carb cleaning.

Fix the fuel leak and test run it. If it makes adequate power, use it and don't worry about the compression. You are smart to not trust the HF tester. They make some great bargain tools (and their best tool boxes are fantastic), but anything from them that has to measure absolute values is suspect. I doubt there's any way to trace the calibration of that compression gauge back to a standard. It's a good tool for checking for differences in compression between cylinders though and the fact that you saw none is an excellent sign.

Denny Crane · 10-02-2019, 09:23 PM

Thanks one again for seeing this thru!
The picture is upside down but the fuel is coming out of the hole in the center of the top carburator. I believe this hole is from the top where the prime tube is attached
Everything was stripped, dipped and soaked in cleaner, new gaskets, floats, needle, gas lines.
Could the primer solonoid keep priming?

Dave R · 10-03-2019, 06:55 AM

Quote:

Originally Posted by Denny Crane

Thanks one again for seeing this thru!
The picture is upside down but the fuel is coming out of the hole in the center of the top carburator. I believe this hole is from the top where the prime tube is attached
Everything was stripped, dipped and soaked in cleaner, new gaskets, floats, needle, gas lines.
Could the primer solonoid keep priming?

I doubt it's the primer solenoid, that would affect all three carburetors and it cannot force fuel into a carburetor (it's just a valve that lets extra fuel in when the engine is so cold that the fuel comes out of suspension which makes it hard to start).

The fact that the floats and needles were changed means it's even more likely something went wrong with the float and needle. They are quite fiddly and easy to screw up, and if you know anything about part failures and "bathtub" curves", a brand new part has a higher likelihood of failure (infant mortality) than one that's been proven to work over time...

Pull off the carb that's leaking, take the bowl off and see what's up. My guess is that the float has fuel in it, the needle valve has a defect in the rubber tip, the clip on the needle fell off, the pivot shaft is displaced or the stamped metal hinge lever is bent (which typically results in incorrect float height).

ApS · 10-03-2019, 08:54 AM

Quote:

Originally Posted by Denny Crane

Thanks one again for seeing this thru! The picture is upside down but the fuel is coming out of the hole in the center of the top carburator. I believe this hole is from the top where the prime tube is attached Everything was stripped, dipped and soaked in cleaner, new gaskets, floats, needle, gas lines. Could the primer solonoid keep priming?

It's likely the float that's jammed open, allowing gas to leak out.

Gently run a clean probe through the large single hole that's leaking, gently tap a few times, and see if that clears the jammed float.

You might even feel the float return to normal.

Woodsy · 10-03-2019, 09:57 AM

What Dave R said!

Woodsy

09-09-2019, 04:47 PM	#1
Denny Crane Senior Member Join Date: Mar 2010 Posts: 98 Thanks: 28 Thanked 21 Times in 17 Posts	Outboard Compression After purchasing a pontoon boat a few years ago for the lake I am thinking of getting my 22' back on the water for a few salt water trips each year, nothing hard core. It has a 1985 evinrude 175 hp vro 2 stroke. New gas, plugs, etc, has spark and almost fires up. When I did a compression test each cylinder was 61 psi. When I first got the boat 10 years ago compression was 89 each but I was told evinrude runs a little lower than others. My question is before I get into cleaning and rebuilding carburetors can anyone tell me whether I should bother or not, given the compression numbers. I don't know the ranges of good/bad compression and whether I should just shop for another older engine. While I love my newer Mercury 4 stroke on my pontoon, I like to tinker and don't know when to call it quits sometimes. I doubt a shop will work on something this old. Thank you!

09-10-2019, 03:11 AM	#3
ApS Senior Member Join Date: Jan 2005 Location: Florida (Sebring & Keys), Wolfeboro Posts: 5,788 Thanks: 2,085 Thanked 742 Times in 532 Posts	MMO--FLL Approved... Add some Marvel Mystery Oil directly into the cylinders, let it soak a few days, use starter fluid to keep it running or stuttering a few minutes, and retest compression when cold. (Or warm like before). Use the same gauge, then retest with another. Your former 89 is OK for a 2-stroke. A substitute for MMO is automatic transmission fluid, but it's missing the minty odor. __________________ Every MP who enters Winter Harbor will pass by my porch of 67 years...

09-30-2019, 01:17 PM	#11
Denny Crane Senior Member Join Date: Mar 2010 Posts: 98 Thanks: 28 Thanked 21 Times in 17 Posts	Follow up good news! Thanks for all your help with a motor that was destined for a salvage yard. I bought carb kits for 3 double carburetors, dismantled them, soaked them in a gallon cleaner kit from Advanced Auto, put it all back together having help from pics I took. I changed the primer solonoid and I used fresh gas and evinrude 2 stroke oil. For the first time since I owned this boat it started on the first turn of the key. I didn't have time to do another compression test but I will. However, once it started after using the primer bulb, it would stall after running for a minute. I would prime, start, run til it stalled continuously. Next questions or advice: Should I change the vro pump which mixes the fuel and oil? It's not a cheap part but i don't know if there is anything else I should troubleshoot or test first. it has all new fuel lines and fuel filter. Thanks again

10-01-2019, 09:48 PM	#13
Denny Crane Senior Member Join Date: Mar 2010 Posts: 98 Thanks: 28 Thanked 21 Times in 17 Posts	Update Next round! My engine started beautifully and kept running this time, however gas kept pouring out of the hole in the top hole front face between the 2 carburetors, mostly the top carburator. The primer hose goes into the top of each carberator. I did change the primer solenoid parts, not the whole solenoid. The gas kept flowing down the front face. I checked the compression again after it ran, full throttle, and each cylinder was once again 60psi. I will admit the compression kit is from harbor freight. I may be at my limit here, but I'm close. Sorry the pic is upside down. Attached Images Last edited by Denny Crane; 10-01-2019 at 10:27 PM.

10-02-2019, 09:23 PM	#15
Denny Crane Senior Member Join Date: Mar 2010 Posts: 98 Thanks: 28 Thanked 21 Times in 17 Posts	Thanks one again for seeing this thru! The picture is upside down but the fuel is coming out of the hole in the center of the top carburator. I believe this hole is from the top where the prime tube is attached Everything was stripped, dipped and soaked in cleaner, new gaskets, floats, needle, gas lines. Could the primer solonoid keep priming? Attached Images

09-09-2019, 10:47 PM	#2
Descant Senior Member Join Date: Mar 2006 Location: Merrimack and Welch Island Posts: 4,031 Thanks: 1,211 Thanked 1,511 Times in 983 Posts	Some older, more experienced mechanics ("technicians") love the opportunity to work on older engines. e don't all ahve confience in additives, but if a little STP improves the compression, that might give a sense of direction. Why did the numbers drop if the engine hasn't been used for several years? Most professional mechanics disavow the value of ethetr (Starting fluid, weasel piss in my day) but it may help to fire he engine and burn ot wateber old gas is in the system until you can get fresh gas flowing,. with some anti E-10 stabilizer. Your engine may need to be re-tuned to compensate for E-10. I don't know. just free lancing my old time thoughts. It used to be simple: air, fuel, ignition. Now it's air, mixed fuel, ignition, electronics. "There's an app for that."

The Following User Says Thank You to Descant For This Useful Post:
Denny Crane (09-11-2019)

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Denny Crane (09-11-2019)

09-10-2019, 06:56 AM	#4
8gv Senior Member Join Date: Jan 2012 Posts: 2,009 Thanks: 61 Thanked 701 Times in 455 Posts	I have yet to try this product but it was recommended to me by a tech on the Mercury service phone line. He said it can make a big difference. Mercury/quicksilver W Power Tune At 12 92-858080q03 https://www.amazon.com/dp/B00BO88QIK..._m74DDbJM3SAYZ

The Following User Says Thank You to 8gv For This Useful Post:
Denny Crane (09-11-2019)

09-13-2019, 11:54 AM	#5
Dave R Senior Member Join Date: Jul 2004 Posts: 2,974 Thanks: 246 Thanked 736 Times in 438 Posts	The odds of all the cylinders having the the same low compression are really slim and it may just be a problem with the gauge or test technique. Normally, as the engine wears, you'd expect the range between cylinders to increase. Did you open the throttle for the test? A closed throttle would likely make all the cylinders read low, especially on a two stroke where you are counting on the air rushing in to spread the oil/fuel mix around and lube the rings. I would spend the time and money to get it running then see how it works. If the compression is really low, it may be due to stuck rings and it might improve after you flog it a bit under load.

The Following User Says Thank You to Dave R For This Useful Post:
Denny Crane (09-17-2019)

The Following User Says Thank You to 8gv For This Useful Post:
Dave R (09-16-2019)

09-21-2019, 08:21 PM	#7
Cal Coon Senior Member Join Date: Apr 2018 Location: Lakes Region Posts: 475 Thanks: 179 Thanked 158 Times in 100 Posts	I have heard that Yamaha ring free is really good stuff. Can't hurt to try, and I would also put some good old fashioned Marvel Mystery oil in them cylinders. That stuff can work miracles sometimes...

The Following User Says Thank You to Cal Coon For This Useful Post:
Top-Water (09-24-2019)

The Following User Says Thank You to Dave R For This Useful Post:
Denny Crane (09-30-2019)

10-02-2019, 05:41 AM	#14
Dave R Senior Member Join Date: Jul 2004 Posts: 2,974 Thanks: 246 Thanked 736 Times in 438 Posts	I do not understand where the gas was pouring from based on your description, but it sure sounds like nothing more than a sticking float in the carburetor that was dumping fuel. If I am right, the bowl probably has some ethanol-caused crud in it. I would clean all the carbs if it were my engine. I don;t know of any additives that will dissolve the crud, sad to say. I imagine youtube would be a great resource for instructions about carb cleaning. Fix the fuel leak and test run it. If it makes adequate power, use it and don't worry about the compression. You are smart to not trust the HF tester. They make some great bargain tools (and their best tool boxes are fantastic), but anything from them that has to measure absolute values is suspect. I doubt there's any way to trace the calibration of that compression gauge back to a standard. It's a good tool for checking for differences in compression between cylinders though and the fact that you saw none is an excellent sign.

The Following User Says Thank You to Dave R For This Useful Post:
Denny Crane (10-02-2019)

The Following User Says Thank You to Dave R For This Useful Post:
Denny Crane (10-03-2019)

10-03-2019, 09:57 AM	#18
Woodsy Senior Member Join Date: May 2004 Location: Weirs Beach Posts: 1,949 Thanks: 80 Thanked 969 Times in 432 Posts	What Dave R said! Woodsy __________________ The only way to eliminate ignorant behavior is through education. You can't fix stupid.