1989 Merc 100elpto unexplained power loss

"I began experiencing a proble

"I began experiencing a problem with my boat this year, and have spent more time and money than I can afford attempting to diagnose and repair the problem. I am hoping that this will help.

Here are the symptoms: I accelerate to full throttle and after about three minutes the engine begins to slow. If allowed to continue, the motor will shut down. It will restart but seems to miss in at least two cylinders. If allowed to cool, it will run well again, until I open it up again.

These are the things we have done in attempting to repair it. Compression tested and was good in three and acceptable in the other. Spark tested and is good now. Replaced all of the following parts hoping to find the culprit: Stator, Power Box, 2 coils, water pump impellor, rebuilt fuel pump. Removed and thouroughly cleaned all the carbs. Replaced the inline fuel filter. Pumped out boats gas tank and cleaned. Replaced spark plugs. Replaced fuel line quick connect. Checked all fuel line fittings for air leaks.

It simply just keeps losing cylinders under heavy load. Then runs rough and misses until completely cooled.

Can anyone help me????????"

"Hi,

What's accepable c

"Hi,

What's accepable compression in last cyl?

Is telltale peeing strong when on the plane? Sounds like the water channels are blocked due to pvs impeller have been chewed up?

Lost spark is a protection to get back to dock.

Is it using oil? Check this and try pre-mixing some gas @ 50:1. It'll smoke like an old pirate, but you'll be on the safe side until we've seen further.

Check this and we'll go from there."

"Wow. Early riser.

Peein

"Wow. Early riser.

Peeing is strong on plane. Forgot to mention I replaced the impellor yesterday. Old one was cracked, but still intact.

It is leaking oil somewhere under the carbs, but my mechanic didnt seem to think that was a problem. Are you suggesting I run a different gas tank premixed? The oil level hasnt changed much since this started. Hard to tell if its abnormal.

Also, this symptom only shows on the water.

Will wait for your responce prior to acting."

"Also, compression from bottom

"Also, compression from bottom to top was 110, 110, 90, 110."

"Donnie, that "leaking oil

"Donnie, that "leaking oil" could be indicative of a bad crank seal.

A bad seal could account for all your symptoms. If a seal is bad (or going) you lose your gas/oil/air mix out of the lower crankcase which results in a less than optimal charge to the cylinders (and leaves a tell tale skim of oil in the lower cowl when the gas evaporates and leaves the oil behind).

Your cylinder compression sounds good (even the 90 is marginally ok), but if you are losing pressure in the crank case (and more as it warms up and the metal expands a little bit) then your motor could be starving for fuel."

"Crank seal looks ok. Oil lea

"Crank seal looks ok. Oil leak seems to be in front of and underneath carbs, around the nest of hoses delivering oil."

Powerhead base gasket?

Powerhead base gasket?

Well... Thanks for the ideas b

Well... Thanks for the ideas but it turns out we were all wrong. 3 carb was blocked when I got it and 3 cylinder was at 90 then. Just snowballed from there I guess. Compression testing today showed 125 in all the other cylinders and 0 in 3. Completely burned out cylinder! Going to rebuild. Will be back with questions for you!

What a great resource!