Low compression in all 6 cyclinders

[Tremayne]

I have a 1985 235 Evinrude V6. I did a compression test on it, I get 60 lbs in all cyclinders. Also I notice when I run the motor on the hose it cranks fine, but when the prop is in the water I have to have the throttle wide open for it to crank. Once running it idles very rough, sometimes stalling. Could this be from the low compression? What could cause all 6 cyclinders to read 60 lbs? Any help will greatly be appericated! Thanks for your time.


Tre

 

[tashasdaddy]

Re: Low compression in all 6 cyclinders

i think i would do a decarb on the motor, and check the readings again. you might even try a different guage, before. turn the motor over till the readings quit going up. you have equal compression that is the most important thing. the rough idle could be dirty carbs, have you checked the spark on all 6 cylinders?

 

[freddyray21]

Re: Low compression in all 6 cyclinders

low or uneven compression can cause a rough idle. but for all 6 to be equal and low I would also suspect the gauge. Like said do a decarb and check again.

 

[kenmyfam]

Re: Low compression in all 6 cyclinders

I'm with the "check it with another gauge" as well group.

 

[Tremayne]

Re: Low compression in all 6 cyclinders

Thanks to all for the quick responses. I will clean the carbs and try a different gauge. Thanks for your suggestions. I will keep you all posted on the out come.

Tre

 

[clanton]

Re: Low compression in all 6 cyclinders

This engine could have low compression head gaskets, I would do what Tdaddy said, make sure you have spark all cylinders, clean carbs, look at the stator for meltdown.

 

[CATransplant]

Re: Low compression in all 6 cyclinders

I think you'll find that a different gauge will give you different readings. It's exceedingly rare for a 6-cylinder engine to read evenly and consistently low on all cylinders.

Your idling problem is most probably dirty carbs. A complete cleaning and installation of carburetor kits will probably solve that problem.

Just for your information, cranking means turning over with the starter. It doesn't mean starting. If an engine cranks it means it turns over when you use the starter. If it runs (or fires) it means that it runs.

Lots of people confuse the two terms, and that causes confusion when you ask questions. Obviously, your engine cranks, but is hard to start. Two different problems...many different answers.

 

[R.Johnson]

Re: Low compression in all 6 cyclinders

What ever you do, don't take the cylinder head off! That would answer the question, and you would lose all that dancing around. If that guage is correct, which I doubt, 60 lbs. all the way around does'nt sound right.

 

[freddyray21]

Re: Low compression in all 6 cyclinders

What ever you do, don't take the cylinder head off! That would answer the question, and you would lose all that dancing around. If that guage is correct, which I doubt, 60 lbs. all the way around does'nt sound right.

let's take the heads off of all of them whether they need it or not. Before taking the head off see if the gauge is any good. For all to be at 60lbs makes me thing the gauge won't go any higher.

 

[jonesg]

Re: Low compression in all 6 cyclinders

The first time the mechanic checked my compression it was 30psi on all 6, the engine was in running but misfiring condition, so he bought another guage and it jumped to 65psi.
I bought my own guage at autozone , did a bit of seafoam in the cylinders, ran it and I got 85 all round (V6).
Turned out to be the powerpack.

 

[Tremayne]

Re: Low compression in all 6 cyclinders

I checked the compression again with my dad's Mac tools compression kit. I got better results, all but one between 90 and 95 psi. Still got one low at 80 psi. What could be the problem with the low cyclinder? Is the clean the carbs a hard task? I called a marine mechanic he quoted me $250-$300. That sound a little high. My dad is a diesel mechanic I think he should be able to tackle this task. Thanks for all the help you all have provided to me.

 

[tashasdaddy]

Re: Low compression in all 6 cyclinders

your dad should be able to handle the carbs, these are basic directions, but your carbs are a little different. http://forums.iboats.com/showthread.php?t=244013

he can see the complete carb diagram here just follow the prompts.
http://shop2.evinrude.com/ext/index.aspx?s1=bf6ad09c53cead335fcfd8a6471c0f7f

after the carb rebuild do the decarb, it has been know to free up stuck rings, and bring compression up.

http://forums.iboats.com/showthread.php?t=158076

i would buy a original service manual, because after the carb rebuild i would do a link & sinc. which is a sept by step procedure, in the manual for your particular motor, that synchronizes the spark advance, and the carbs so they work together, at the proper time.

http://www.outboardbooks.com/index.cfm?fuseaction=models.main&year=1985&ID=67162

 

[Tremayne]

Re: Low compression in all 6 cyclinders

tashasdaddy, thanks for the links we will give it a shot and let you know the out come. Would the carbs be the reason that it will not fire when the prop is submerged?

 

[freddyray21]

Re: Low compression in all 6 cyclinders

it will not fire when prop is submerged or will not start? two different things. Those compression numbers are not bad and I would not worry about the low cylinder now. Get the carbs cleaned out and do a decarb on it and then see what the numbers are.

 

[jonesg]

Re: Low compression in all 6 cyclinders

Your numbers are better than mine,
I did all the carbs, first carb took 2 hrs, the last carb took 10 minutes.
Then seafoamed it.

Ran the boat first time in the water yesterday, pushed it full open and I almost went out the back of the boat.! Wasn't ready for that.

 

[tashasdaddy]

Re: Low compression in all 6 cyclinders

when running on muffs there is not any backpressure on the exhaust. thus the idle has to be set around 1,000 rpms on muffs, for it to idle/start in the water. in THE WATER and IN GEAR, it should idle @600-750 rpms. this has to be fine tuned in the water.