86 force 125 low compression in one cylinder

nabularach

Banned
Joined
May 18, 2008
Messages
52
I have only 70 psi in one cylinder and about 110 in the other three. Do I need to pull the case apart or is there any other options.
 

john from md

Commander
Joined
Apr 13, 2008
Messages
2,184
Re: 86 force 125 low compression in one cylinder

Its a long shot but you should do the decarbonizing procedure with Seafoam first. It is always possible that you have a sticky ring and it is by-passing. Whether the procedure will work or not is pure speculation but, if it doesn't, you are only out $7 and some gas and time.

I believe the procedure is listed in the faq.

Regards,

John
 

nabularach

Banned
Joined
May 18, 2008
Messages
52
Re: 86 force 125 low compression in one cylinder

thanks John, I will order the sea foam now and give it a shot. The other question I have is, My motor was running fine then suddenly began to run horrible. It would only start with throttle then die in neutral. I replaced the fuel pump diaphram gaskets and filter. I had to adjust the idle stop screw just to keep it running in neutral and when I try to run wide open it only revs upto about 1/3 of the rpm's and then slowly dies while driving. The other thing I noticed is that If I start it with full throttle the rpm,s are much lower than they should be. Any Ideas?
 

john from md

Commander
Joined
Apr 13, 2008
Messages
2,184
Re: 86 force 125 low compression in one cylinder

The best thing to do in these matters is to think systematically. Eliminate one thing at a time and note any differences.

From my own experience, I found that replacing the fuel pump wasn't enough but I didn't look further in the fuel pump area. I went on to rebuild carbs and replace fuel line etc. but still had running problems. It turned out to be the three check valves in the pump were sticking.

I would suggest that your engine is leaning out and you should start with the fuel system. Clean the carbs out good with some WD40 or carb cleaner. Also, low compression can play hell with your fuel pump as it uses compression to operate. What is the fuel ball condition when this is happening? Is it still hard, collapsed, soft?

Why don't you clean out the carbs, clean the plugs and give it a Seafoam treatment and then check back.

Regards,

John
 

nabularach

Banned
Joined
May 18, 2008
Messages
52
Re: 86 force 125 low compression in one cylinder

I will try to clean the carbs this weekend. The fuel ball is firm and if I pump it while the motor is running I get no change in rpm's
 

john from md

Commander
Joined
Apr 13, 2008
Messages
2,184
Re: 86 force 125 low compression in one cylinder

Don't forget to do the decarb afterwards to see if it helps your low compression problem. If you have a strong flashlight, you can shine it in the plug hole and see the carbon. After you decarb it, you will start to where the aluminum and carbon separate. Sometimes it takes two or three times to clean up an engine with heavy carbon build up. Don't forget to clean the plugs in between cleanings and when you are through.

Regards,

John
 

jerryjerry05

Supreme Mariner
Joined
May 7, 2008
Messages
17,923
Re: 86 force 125 low compression in one cylinder

The comp for that motor should be 150# each.
Take all 4 plugs out,open the throttle all the way and test again(might be your guage).
Take a long thin screwdriver or bent piece of coat hanger and feel for scratches on the cylinder wall. If you can feel them then the problem is more serious.Jerry
 

nabularach

Banned
Joined
May 18, 2008
Messages
52
Re: 86 force 125 low compression in one cylinder

I checked the compression on the motor when it was cold. Do you think it will make a big difference if i check it after it is warmed up?
 

john from md

Commander
Joined
Apr 13, 2008
Messages
2,184
Re: 86 force 125 low compression in one cylinder

You will get some increase with a warm engine and if you squirt oil in it it may also show a little increase. Nothing will bring it up to where it should be until you free up the stuck rings (assuming this is your problem).

The only thing to do at this time is to do a real good decarb. After that you can measure the compression and compare the readings with your previous readings. If the numbers go up significantly, then you know carbon is your problem. If they do not, I would suspect mechanical problems like a blown headgasket or broken rings.

Regards,

John
 

fab9racing

Seaman Apprentice
Joined
Jun 16, 2008
Messages
42
Re: 86 force 125 low compression in one cylinder

I would like to make a suggestion buy you a head gasket it will cost u $30.00 you could have a leaking head gasket, how ever it will take all the guess work out and save you some time, while you have the head off you can look at the pistons and cylinders and you will see if you have a peoblem:)
 

nabularach

Banned
Joined
May 18, 2008
Messages
52
Re: 86 force 125 low compression in one cylinder

Now that you mention the head gasket, I noticed when I pulled the plug with the low cylinder it looked like it had a bit of water on it. When my head gasket went on my dirtbike it was dumping all my coolant into the cylinder. Would a wet plug be a blown head gasket indication?
 

fab9racing

Seaman Apprentice
Joined
Jun 16, 2008
Messages
42
Re: 86 force 125 low compression in one cylinder

if you have water in the cylinder this is a good possibility it only takes a minute to change the head gasket, and it is a good maint item that is cheap and you will have the best inspection it will tell you how the cylinders look and believe me you will see gouges if it has a bad ring, good luck
 

nabularach

Banned
Joined
May 18, 2008
Messages
52
Re: 86 force 125 low compression in one cylinder

I pulled the head off yesterday and the head gasket was blown and there was water in 2 cylinders. I put a new one in and the boat ran great.



Thanks Guys
 
Top