[DocBob]

I've been having engine issues this summer (no power) so I did a de-carb...Holy Smokes!!! No pun intended but I'm surprised the neighbors didn't call the fire dept.

I also replaced the plugs and was testing each cylinder for spark so I had started and shut down the motor a total of six times for a few seconds each cylinder (I do have good spark at each). I already pulled and cleaned out the carbs and did verify fuel to all cylinders.

Anyway, I noticed what looks like crude oil around the prop and on the through the hub exhaust...I did not notice this before as I was on the water, so I don't know if it was present prior to the de-carb. Now I know there's going to be a bunch of crud coming out the exhaust (I've de-carbed before) but I don't remember it looking like oil. This is like pure black/gray thick crude oil, no gas smell. This is within a few seconds of starting the motor at idle speed. And by the way, I replaced the impeller last year and telltail worked perfectly when on the water so I don't think there has ever been an overheating issue...at least none that I'm aware of.

L/U oil is perfect, no metal, no water.

I just did a quick compression test and that looks good (all 6 cylinders fall within a 99-107 psi range)...unless that is considered really low for a V-6 mid-eighties Mariner outboard???

Is this just the crud from the decarb, or should I be worried? Am I safe to run the motor to see if it clears up after awhile? Or should I check something else first.

[86RajunCajun]

99-107 psi compression is very low and usually means the rings are worn, or there is other internal problems. If they are all 6 at that level then i would say its the rings. Rings are cheap and easy to replace so thats a good thing for you.

My 1986 V150 only has 340 hours on it and i have 120 psi compression on all 6 cyls.

The oil in the exhaust may be from the residual oil/fuel mix that isnt being burned and is a result of "blow by". In other words, it isnt being burned off and is being blown past the rings on the compression stroke and then pushed out the exhaust on the exhaust stroke when the piston goes all the way down it kinda squeegies the left over oil/fuel back up and out. The rings would likely seal enough to push the oil/fuel back up and out because there isnt the compression that you have on the compression stroke on the exhaust stroke.

Then again is may just be carbon from the decarb. I dont see why it wouldnt be ok to run it as long as you have the correct oil/fuel mix and everything else seems fine. Low compression just means less power.

Take it out and run it good and see if it clears up, even if it does, consider re ringing the pistons as this will bring back a lot of power if your down that low on cylinder compression.

GL
RC

[DocBob]

Hey RajunCajun...thanks for the input. I guess I better make sure my tester doesn't just naturally read low before I plan a re-ring (especially since that job is above my mechanically declined level of expertise), but if it is worn rings, that would certainly help my power/performance.

Anyone know what the "normal" or factory compression on this motor should be?

[86RajunCajun]

Those cyl's with good rings and walls/pistons should get you in teh range of 120 psi new....115 with some wear and by the time they get to 100 or around there they need re ringed.

GL
RC