HELP!!! 35psi compression. And it runs

[Jstumbough]

I just bought this boat, i have yet to get it in the water. As soon as I got it I went through it, dumped the old gas and put in fresh non ethanol 93 octane as well as fresh spark plugs. It starts up like a champ and will idle fine. But it seems like its missing and every few seconds it bogs down and shoots out a big puff of exhaust smoke, violently shakes the motor, then recovers.

I just did a compression check (used two different gauges) and no matter what, warm or cold, wet or dry, it's reading 35 psi on all 3 cylinders.

So here are some Questions:

Is there anyway my readings could be flawed?

Should a motor be able to run with such little compression, especially with high octane fuel?

Are there any other problems that could produce my results besides worn rings?

This is my first Motorized boat, so any insight would be greatly appreciated. I consider myself to be capable working on cars and such but two stroke marine engines are not within my comfort zone. However I'm not too timid about turning wrenches on something new so I'd like to fix this myself.

Thanks a lot for any help.

 

[JB]

Re: 1998 Tracker pro series 60, low compression

Re: 1998 Tracker pro series 60, low compression

Howdy, jstumbough.

Welcome to iboats.

Tracker outboards were made by various makers over the years. We need a model number so we can determine the maker.

Since your outboard starts and runs I really doubt that you have all cylinders going bad the same amount at the same time. I don't think 35psi is enough to get it to run.

I suspect something flawed in your technique. Weak battery, leaving the plugs in the cylinders not being tested, etc. Check out the procedure in the Engine FAQs Forum.

Let us know what you find.

 

[Jstumbough]

Re: 1998 Tracker pro series 60, low compression

Re: 1998 Tracker pro series 60, low compression

The engine was made by mercury.

I can get the model number off of it tonight.

I figured I was missing something when I got 35psi. Just not sure what yet. All plugs were out, battery charged,etc.

Thanks.

 

[Jstumbough]

Re: 1998 Tracker pro series 60, low compression

Re: 1998 Tracker pro series 60, low compression

Ok, here's the model number on my outboard: 60 ELPTO

Tracker by Mercury Marine Pro Series 60
Model year: 1998

It was built in December of 1997. Not sure if that matters, but it was on the sticker as well so why not.

 

[Jstumbough]

Re: 1998 Tracker pro series 60, low compression

Re: 1998 Tracker pro series 60, low compression

Also, compression check again tonight with a 3rd brand new gauge, 35 psi.
This time I tried at full throttle, no throttle. And with the motor trimmed all the way up with a little oil in the bores. And all the way down. Also let it run almost an hour before tests. No spark plugs, and a full battery (14 volts on voltmeter).

 

[Jstumbough]

Re: 1998 Tracker pro series 60, low compression

Re: 1998 Tracker pro series 60, low compression

UPDATE:
I spoke with a few people and arrived at the conclusion that I should ignore my compression test readings and find another cause for its running issues. I have since removed the fuel tank, cleaned it and re-sealed everything. I replaced the fuel line, removed the pickup screen in the tank and installed a inline screen filter. It's still having issues though.

Any suggestions on what direction I should go in?

Thanks.

 

[Jstumbough]

Re: HELP!!! 35psi compression. And it runs

Bump

 

[F_R]

Re: HELP!!! 35psi compression. And it runs

Seems impossible that it would run at all with only 35psi. Beats me. Must be one tough engine.

 

[Chip Chester]

Re: HELP!!! 35psi compression. And it runs

What gauge are you using, and can you post a pic of the scale? And your gauge hook-up method?
Chip

 

[Jstumbough]

Re: HELP!!! 35psi compression. And it runs

I haven't quite figured out how to post pics yet. But the gauge went from 0-200 psi. It was labeled in 20psi increments, 0,20,40,60,80 etc. with unlabeled marks every 2psi. I hooked it straight to the spark plug hole using only the hose and adapters in the kit. Checked that all o-rings were intact and in good condition. Also, against the manufacturers suggestions, i used a wrench to ensure they were snug against the cylinder head. Thanks and hopefully my description helps paint the picture.

 

[F_R]

Re: HELP!!! 35psi compression. And it runs

OK, this is a dumb question on my part, and not accusing you of anything, but are you cranking it till the gage quits going up? And/or cranking it with the electric starter? I have to assume you know what you are doing, but .... I had to ask.

 

[Jstumbough]

Re: HELP!!! 35psi compression. And it runs

Yes, I'm letting it bump the needle five times per cylinder test. And I am using the electric starter motor with the battery on a full charge.

 

[F_R]

Re: HELP!!! 35psi compression. And it runs

Sounds OK. The number of compression strokes is not important, as long as it is as high as it will build up. I still don't know how it runs on such low compression. Interesting topic.

 

[Jstumbough]

Re: HELP!!! 35psi compression. And it runs

That's what is confusing me. I'm wondering if there is anything internal that could cause it to not have any compression besides the piston and rings. Like the reeds or something. I just can't seem to figure it out.

 

[steelespike]

Re: HELP!!! 35psi compression. And it runs

The bog down with the shake and recover sounds like a lean sneeze.
Maybe bad upper or lower crank seals could decrease the crankcase pressure and lower the the charge going into the cylinders.
an upper seal would probably be obvious with an oily film under the flywheel.
On smaller motors you can hear the puck puck compression sound from the crankcase when you crank it with the plugs out.

 

[Jstumbough]

Re: HELP!!! 35psi compression. And it runs

Thanks for the info steelespike, I'm going to look into that for sure. The adjument screws on the carbs are all about one turn out from the seat. I think the factory service manual I've got suggests 1 1/4 out as a starting point. Is a 1/4 turn enough to cause a lean condition?

Also, if I recall, there is no sign of an upper seal leak, but every time it stumbles, a puff of exhaust smoke shoots out from under the engine. Could that be the lower seal?

 

[hotrod53]

Re: HELP!!! 35psi compression. And it runs

I just had a friend get strange results like this on a freshly rebuilt Harley motor. He found that if he opened the throttle during the test, he had great compression, with the throttle closed it was very bad. I noticed that you tried opening the throttle at least once.

You could try an old trick that I have used on 2 stroke Lawnboys, put a squirt of 2 stroke oil in the cylinder and test it. On a worn out lawnmower, that will seal it up and raise the compression temporarily. Not that this will fix your problem, but I would be curious what it would do to the reading. That may confirm or excuse a worn ring condition.

Yamaha makes a product called RingFree that I was told by an outboard shop owner will clean out the engine and free up stuck rings if that is your problem.