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!

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."

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. ;)

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 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.

This is a common mistake!

Good point.

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...

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

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.

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

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

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.

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.

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).

Probe...
 

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. :)

What Dave R said!

Woodsy

Success!
 

My 1985 Evinrude 175 lives on! Thanks Dave R and all who walked me thru different steps and ideas. I ended up taking apart the top carburetor that was leaking and the new float wasn't dropping enough. My manual said it should drop between 7/8-1 1/8" so I made the adjustment. It started with the first turn of the key and kept on running! I was ready to buy a new fuel pump earlier so you saved me over $400 for just that part. I don't mind tinkering with an old engine if I can get more time out of it. I think I'm at my limit mechanically so if anything else comes up it might be the end! Thanks again.

Congrats on your victory!

About being at your limit:

Every time one moves forward into unknown aspects of a mechanical project a new precedent of knowledge is established.

Because you continued to be persistent you now know more than you did before.

The limit gets moved down the road each time.

That's great news. For me, there is a tremendous satisfaction in being able to fix something and even more satisfaction in being able to teach someone else to fix something. This is the BEST part of the internet, IMO.

FWIW, I learned something here too, prior to this thread, I knew absolutely nothing about VROs... They are pretty neat.

Not even close. The next thing that comes up just means you get to learn something else and maybe get to (justifiably) buy more tools. It gets easier and easier the more you do it.

One of my favorite recent troubleshooting events happened like this:

My wife and I were visiting our slip neighbors on their boat after dinner one evening this past Summer. The boat captain is very handy and the conversation eventually turned to boat troubles. He confessed that he was confounded by a problem with his generator. 3 minutes later, we're in the engine room troubleshooting, of course. Mind you, it was probably 9 PM by then, but we are both kind of OCD about this kind of stuff...

Anyway, the genset would not crank and the battery and starter worked fine. He had found and replaced a faulty "ground" cable (problem 1) on the engine earlier that day with no improvement. I took a quick look and noticed that there was an arc suppression diode on the starter solenoid. I got my DMM and tested it, and found it was shorted (problem 2). Removing the diode did not help (it can work without the diode, it's just there for solenoid longevity) so I suggested the main controller board had been damaged by the shorted diode and a few minutes later, proved it (problem 3). The main board had acted like a fuse and one of the copper conductors (lands) on the board had been vaporized. I went back to my boat and got my butane soldering iron, a spool of solder, and a piece of bare copper. A few minutes later, the board was fixed and the engine was finally cranking over like it should. Unfortunately, it would not start. On to problem 4...

We determined that the engine was not getting fuel, so the first check was the fuel filter which was clogged (problem 4), we cleaned it out only to discover the engine was still not getting fuel. Next step was to look at the fuel pump. We opened it up and found that water in the gas had caused it to rust a bit and lock up (problem 5). We freed it up and got it working again pretty easily, put it back in place and still got no fuel flow. We traced the fuel line back to the tank and found a check valve at the top of the tank. We took it off and found it had rusted closed (problem 6). Like the fuel pump, it took little effort to get it working again and we got it re-installed. Now the engien was getting fuel, but it still would not start...

The next obvious check was the carburetor. We took it off, took it apart and found lots of crud. There was one particular chunk of crud blocking the pilot jet completely (problem 7) and when we removed it, put the carb back on the engine, and cranked it, it fired right up and the genset has worked great ever since.

We put a new diode on the solenoid the next day and added a fuse so that it cannot cause the same problem again. We also got rid of the water in the fuel tank.

That's my idea of an interesting evening. FWIW, I had only recently learned about arc suppression diodes this year, on the internet, and if not for that, I think we would have never got past problem 2, that night. I also just happened to have a bag of 100 spare diodes on hand (that I got on ebay for a couple of bucks) because my 27 year old boat has them installed on every one of the dozens of switches and relays.

What a great adventure!

You are a true Doctor of your craft! You had me lost at "the genset would not crank!" Thanks again.

Outboard Voltage
 

Since this thread speaks to older outboards here's one - My 1987 60HP Johnson which runs great melted it's Rectifier and somehow the engine still ran and has been this way for who knows how long. (only use the boat on occasion)

I do have a service manual and the stator and new rectifier check out OK using a Fluke. However the output from the rectifier is up around 16 Volts which is really too high. Question is - do all the old outboards with Rectifiers run high on voltage? I did order a Regulator / Rectifier which I believe will cure the high voltage but thought it a good question to throw out there. I don't have any electronics on the boat besides Nav Lights but worry about the Power Pack and other engine components burning out. It has eaten a few choke solenoids which I'm now thinking could be a victim of the high voltage.

Thoughts ? - Thanks

As far as I know, the charging system on that engine is unregulated, so 16 volts is probably normal if the battery is charged up fully. It will be a lot lower if the battery is discharged. If you are concerned about too much voltage, CDI makes a regulated rectifier that should bring it down to 14 volts or so. It's part number #193-3408 and they cost about 70 bucks.

Thanks Dave that's what i thought and ordered.

I'm Back!
 

It would have been too easy if my outboard story ended there. The engine was running beautifully in my driveway and I was planning to winterize it when it stopped out of the blue and I couldn't turn it over again. When I went to prime it again I noticed the prime bulb was compressed and I couldn't return it back to normal. Any ideas?

I know where the vent is but I don't know how to check that.

It's either a clogged vent on the fuel tank or a clog blocking fuel from flowing from the pickup in the tank to the bulb. The clog cannot up downstream of the bulb.

Assuming it's not a clogged vent, one common cause of this is a blockage in the fuel line caused by de-lamination of the inner layer of fuel line itself. If the fuel line is more than 10 years old, consider replacing it.

It may also be caused by crud clogging the fuel pickup in the tank. Pull it out and have a look.

There may be a check (anti-siphon) valve where the fuel line comes out of the tank. Check that, might be stuck shut.

Great ideas once again. I changed all the fuel lines from the gas tank out a year or two ago. Come to think about it when I went to siphon the old gas out with a small 12v pump I had trouble pulling gas at first. I may try an external gas tank first and go from there. Thanks!

If there was any sign of water in the old gas, I bet the check valve ball is rusted and sticking in place.