Force 125 Compression Troubles

Hello,

I have a 1987 Force 125. I recently did a compression check and all 4 cylinders registered about 88 psi; far below specifications. All 4 cylinders registered about the same. Any ideas as to what I should check first? Head Gasket? The boat seems to run fine, but only up to about 1/2 throttle and then will begin to cut out. It seems to run perfectly up to about 20 mph.

Thanks in advance for any help you can give me.

Re: Force 125 Compression Troubles

squirt a little 2 cycle oil in each one, do it again.. see if they come up close to spec. Sounds like you did it dry and cold.

Bob

Re: Force 125 Compression Troubles

Sounds like the comp tester is reading wrong maybe old or cheap,
The important thing is that all cylinders are about the same reading.
Check the fuel pump diaphram and do a spark test.
Any soft hoses or blocked lines will cause poor performance.
Inline connectors can leak air.Water in the gas will hurt performance.
Check these things.J

Re: Force 125 Compression Troubles

What spec?? I am aware of no spec for psi, only that all cylinders fit in a 10% span. Those "specs" are in know-it-all heads

There are far too many variables involved to set a spec for psi. Changes (or errors) in engine temp, barometric pressure, guage, battery strength, starter condition, user technique and mysterious other variables can add up to as much as a 50psi difference in measured psi.

The chances that 4 cylinders will all go bad by the same amount at the same time are less than zero.

Your engine compression is fine, 2902ao. Quit worrying about it and find the real trouble.

Outboard hypochondriacs will have you rebuilding the whole cotton picking thing. Talk about fixing what ain't broke!!.

Re: Force 125 Compression Troubles

JB, I like your style!.. I'd like to subscribe to your newsletter! Seriously, I think spec is (guessing) 125-145 psi. But I've always been happy even if they are LOW numbers, if all 4 cyls. are the same, it'll run ok. And yes, I know of 3 PERFECTLY good cylinder heads replaced on Suzuki Veronas because the guy's compression tester was OFF.

the OP's problem was "cutting out" at 1/2 throttle or so.. I say get in there, and make sure ALL the screws holding the wires to the buss bar are tight.... things sometimes work ok with sub-par connections until the load increases and voltages will work ok until up to higher speed/rpm.. Grounds need to be clean and tight... fixing those problems are free, and need NO parts, which = NO spending money!
He could also have coils breaking down at speed, but all the BASICS need to be eliminated first.

Bob

Re: Force 125 Compression Troubles

Thanks for the help. Since all 4 cylinders have about the same compression, I will not worry about it.

I thought at first the problem was the fuel delivery system. I rebuilt the fuel pump and carbs, and checked for restrictions. This made it run better but did not solve the problem.

Now I realize when the engine starts to rev up, one of the plugs quits sparking. I replaced the coils, but it did not help. Assuming the connections are all tight, does this sound like a bad stator? Or, does it sound like a bad cdi unit? Or something else?

Re: Force 125 Compression Troubles

Well, I would not "not worry about it." I would try to find another gauge to borrow and compare--just to be certain. When an unexpected result is obtained with any test, it ALWAYS pays to repeat and confirm. A little extra effort now will pay dividends in saved money and time later.

While Force may or may not have published compression ratios, Chrysler (which was the exact block) did. New or rebuilt, the 125 should have somewhere around 140-145 PSI compression ratio. Of course, if you tested after the engine had been sitting for a couple of months, the numbers would be lower so you would squirt a little oil into each cylinder before testing.

Now, if a known good gauge still shows low compression, then the engine will run and most likely run smoothly, but will lack top end power.

So: once you solve the ignition problems, then it is time to go back and double check compression. Low compression on all four cylinders Could indicate possible stuck rings.

Re: Force 125 Compression Troubles

2902ao how did you figure that at throttle the plug is not sparking? I have I think the same problem. I get spark went I turn it over but how do you test at higher speed?

here is my thread:
http://forums.iboats.com/showthread.php?t=493622

Re: Force 125 Compression Troubles

He is talking about compression, not compression ratio, Frank. Chrysler's fantasy requires (and assumes) a lot of conditions (new or rebuilt), equipment and technique not available to DIY wrenches. I do not consider it a realistic spec.