What to look for if compression is low

[Karla45]

I had the carbs fully cleaned and serviced. THe mechanic told me that the bottom cylinder was not getting any gas and that my carbs were really getting clogged up. He said that after he cleaned them the compression was 135 on 2 top cylinders and 80 on bottom cyclinder. He said he thought that maybe the pistons rings were sticking. He took out for a run and said the compression started increasing to to 100 and that it would continue to get higher as i ran the boat. I took it out today and still having the same problems. I push the handle down to go forward and hardly anything happens then I put it down all the way and evetually it will kick in and then runs great. sometimes it will go 25 with handle all way down and others it will go 30 and above. alot of times i am not able to rev up the engine to get it warm, i push handle forward as far as i can go and nothing happens. It also surges sometimes but not a big surge just a little. It is getting very hard to start and dies in idle alot. I can tell sometimes when i have the boat in idle that the motor is not running very high on idle and that it is going to die. I have a 85HP Force 1989. I have purchased a diapgragm and gaskets for the fuel pump but have not put them in yet. My thoughts were that maybe if the carbs were clogged then the fuel pump has clogs in it too. The boat had been sitting for 5 years before i got it last summer. On the forum i am always seeing the suggestion to check compression, then fuel, then spark. So if compression is low what does this mean, do fuel problems cause compression problems or could it be something bigger?

 

[jason32038]

Re: What to look for if compression is low

If it sat for 5 years you should get a seperate 2.5 gallon tank and mix the proper mix and add seafoam. Run it for an hour while watching to make sure it doesnt overheat and check compression again. Rings might be stuck.

 

[TwoFish]

Re: What to look for if compression is low

Answering your last question first. Yes fuel can cause compression problems. Two stroke engines rely on the oil in the fuel to lubricate them. If a cylinder isn?t getting fuel it can be damaged due to lack of lubrication.

You may have stuck rings, damage to that cylinder, leaky gaskets or seals causing your low compression. Start with the easiest fix first. As mentioned before try using a decarboning method. Seafoam, Quicksilver power tune, OMC Engine Tuner. Use your choice of these as per manufacture?s instructions. You may be lucky and the compression comes back up on the low cylinder. If not you will need to dig deeper.

Having varying amounts of power at full throttle doesn?t sound like a compression issue. I?m only new to working on outboards but I would have thought the power would stay fairly constant. You may have fuel or electrical problem as well.

You said you have parts for the fuel pump. I?d fit them to the pump & also check all the fuel lines for damage. Tighten all the connections on the fuel lines as well.

Have you checked whether the butterflies in the carbys open all the way and the ignition advance mechanism moves when you push you throttle lever forward? You don?t need to have the engine running to do this. You may have some cables sticking. The mechanic would probably have checked this out but worth a look.

Hopefully some of the more experienced people on this forum will have some ideas.

It can be frustrating chasing engine problems.

Good Luck.

 

[jerryjerry05]

Re: What to look for if compression is low

Fill out the profile you might be close to someone who can help.The gas your using has Ethanol. It ruins older rubber.Your motor will need to have all the hoses and squeezie replaced.If there is a quick disconnect in the line remove it.The diaphram in the fuel pump will probably need to be replaced.The line from the tank to the motor,replace.Make sure the gas tank vent is clear,bugs get in there and clog it.
The carbs will need to be cleaned.Be carefull what you use.The spray cleaner off the shelf will work.NO soaks they will ruin the rubber in the needle/seat.
The compression,Seafoam or Mercury's Power Tune.I like PT best.Seafoam is good in the tank. Power Tune,warm the motor and then spray it into all three cylinders.Shut it off and remove the plugs.Spray PowerTune into all 3 plug holes.Turn the motor over by hand.Keep spraying.Then replace the plugs and tilt the motor up and let it set for a couple three days.
Three days later go out and start it.This is after the carbs and hoses have been cleaned or replaced.It's gonna be tough to start and you might need starting fluid.Get the kind with a lubricant.
Then run it. Then do a comp test.Post your results.J

 

[Karla45]

Re: What to look for if compression is low

TO give little more detail. The tank i use is 12 gallon that i used because would have to take up flooring to get old gas tank out and flush and there was some gunk in old tank which had gotten run through the motor because the first mechaninc we took it to did not check all this out like supposed to. I have been running the boat almost every weekend.Carbs have just been fully cleaned by another mechanic this week. Put all new feul line on it in June. The mechanic checked and tightened all hose connections this week. I have moeler inline fuel filter on it since beginning of summer. Can these cause any problems later on or something? I bought a clymer manual and was considering put the diaprhragm on myself but am a little weary seeing that I do not know much about motors. THe manual seems pretty straight forward is there anything I need to be careful about. I had originally thought it was the cables binding because I had taken off some of the electrical tape and twist ties that hold all the cables together and that fixed the rev up issue a couple of weeks ago temporarily. There is alot of electrical tape wraped around the cables. I asked mechanic if this was problem and he said no. I know where the carb butterflies are but have no idea how to tell if they are open by looking. Last weekend I had put seafoam in the tank and that is when the boat seemed to get worse. I never ran all of it through and the mechanic emptied the tank with the seafoam in it. He told me to never use seafoam again. Why i am not sure. I also do not think this is what caused the problems. There is an area on where the cables are running and I it seems like they end up under the bolts that hold the motor to the back. I am thinking of taking a picture to see what you think

 

[jerryjerry05]

Re: What to look for if compression is low

The rebuild on the pump is easy.
Sea foam is good if you follow the directions.Too much is like throwing water in your tank.
Restricting the cables can have a negative affect.They should be free to allow for turning and tilting.Post your pics.
The butterflys are behind the carbs.You will need to remove the carb covewr to see them.J

 

[Karla45]

Re: What to look for if compression is low

I was not able to find mecury power tune anywhere around here. I was told that I could buy something called fabulous blaster at Lowes it is for lawnmowers, outboards and other 2 cylcle engines. Purchased this put in cylinders(followed directions). Afterwards compression 120,120,120. I do not believe that this fixed my problem though. One thing i noticed is that engine rpm would go up and down without me moving the handle, i guess that could be called a surge. When I pull handle back down to slow down it will die alot of the time. It dies while idling alot and at lower speeds. I have not had a chance to take it back out on water to test the problem of bogging down when trying to go. It will not go unless i have the handle all way down then it will start to kick in. I have not taken it out but can tell with motor on the muffs that this is still an issue. Is the primer bulb supposed to stay hard at all times? When I had it on muffs this evening I checked the bulb and I had to pump it to get more gas going through it. I did not notice that there was any increase in rpm when I did this. The motor also backfires sometimes. I have put new plugs in but still get some backfires. I did notice something else that i am not sure is right or wrong. I took a picture of the throttle cam and was wondering if anybody could tell me whether it is line up correctly or not. I took a picture of the throttle cam and was wondering if anybody could tell me whether it is line up correctly or not. I also took a picture of the cables to show where that are under the bolt from motor mount, I have circled this in green and also circled where all the cables are taped together to see if these may cause a problem. The reason I am posting this picture too is that I also have a problem being able to rev up to warm engine sometimes and others I can.

Throttle Cam

Cables

 

[jerryjerry05]

Re: What to look for if compression is low

The carb linkage looks good.
From the front take a picture of the cables,try to get a good shot showing them.They might be too short.They need to flex and move when under way.
Short cables just don't work as good.
When you have trouble reving in neutral that usually means the cables are out of adjustment.
Un-hook the cables.Then make sure the neutral safety switch is in the middle as well as the shifter is in neutral.Then turn the cable end in or out till it just matches the ball connector.
Surging could be a clogged vent or a bad pump diaphram(might be in wrong).
The squeezie could be bad too.I've bought new that are bad.How many filters in the line?Too much restriction will slow fuel supply.
As far as stalling it could be the rpm's too low.You have a tach? What's the RPM in gear and warm at idle?
Remove the tape then retape everything but the cables.J

 

[Karla45]

Re: What to look for if compression is low

Am planning on putting diaprhgam in today. As for the metal parts of the feul pump what can i use to clean with. My guess is that there may be some gunk because old gas got run through it and orange goopy stuff that when dissolved looked like rust. Not using old tank this year but feul pump has probably not been changed for 7 or more years. Would i need to readjust carbs after this? Can i adjust on muffs or is this bad idea? Unfortunately i do not have tach to measure rpm. Also I was told to spray some of the fabulous blaster through air intake while boat is running but I do not know where this is. I looked through manual and could not find any pictures. I am a little confused on adjusting the cables. Where is the neutral switch? Would my manual tell me how to do this, i am needing visuals. 1 inline filter shown in picture. Are you talking about unhooking that cables on the motor where the nuts are?

 

[Frank Acampora]

Re: What to look for if compression is low

First off, get all that electrical tape off the control cables. Force is the only engine that uses the sheath of the cable, not the core, to move the controls. Tied together with tape, the cables are binding each other. Each cable MUST be separate and free to move independently.

Then go up to the top of the page and click on FAQ (frequently asked questions) Read and follow my post on synchronizing carbs and timing.

 

[Karla45]

Re: What to look for if compression is low

When i go to install diaphragm how do i test the check valve to make sure it is functioning properly?

 

[Karla45]

Re: What to look for if compression is low

I may have found some of the problem, there is a hole in the diaphragm but not sure if this is something i did when removing or not. I am not able to get the gasket off because of the screw that i cannot get out until i get the hose off the fitting. Can i synchronize the carbs on the muffs or do i have to be in the water? I am assuming that since there was hole in diaphrgam that i will need to adjust carbs because they were probably adjusted to compensate for the fuel pump problem. I wish I had the money to buy a tach and have installed but funds are tight right now. I will definetly remove all the tape from the cables. Thanks