1982 OMC 90 HP V4, won't start in the water

[Mudbugger]

The title says most of it. 1982 90 HP V4, will start (a bit reluctantly) on muffs, either level or tilted, but when it the lake, it takes a LOT of convincing to get it to start, when it does, it revs up decently, but when you back the throttle off to idle, it dies, and then becomes a bear to start again.
Any chance it could be the back pressure, of the lake water, against the exhaust?
It belongs to my best friend, and he's been fighting with it for a while, today was my first day "testing" things out.
Thanks, Mud

 

[racerone]

My advice is always the same.-----You need to post the actual compression test values.---That is done to determine the overall condition of the engine.----Next is to get the battery load tested.-----No $$$ spent so far.

 

[Mudbugger]

My advice is always the same.-----You need to post the actual compression test values.---That is done to determine the overall condition of the engine.----Next is to get the battery load tested.-----No $$$ spent so far.

The battery is fine, he initially had starter problems, totally unrelated to the present problems. At that time, the battery was changed and even another one was paralleled, the issue was broken brushes inside the starter. A new starter cured that problem.
The engine cranks over at decent speeds, no sluggishness or dragging involved.
I have not checked the compression, as I recall he did, when the cranking issue was occurring, but I don't recall any outrageous numbers.
Being dumb, how would low compression affect starting when the prop is submerged, but not when on muffs?
Just reaching out for logic, not arguing.

 

[havoc_squad]

The battery is fine, he initially had starter problems, totally unrelated to the present problems. At that time, the battery was changed and even another one was paralleled, the issue was broken brushes inside the starter. A new starter cured that problem.
The engine cranks over at decent speeds, no sluggishness or dragging involved.
I have not checked the compression, as I recall he did, when the cranking issue was occurring, but I don't recall any outrageous numbers.
Being dumb, how would low compression affect starting when the prop is submerged, but not when on muffs?
Just reaching out for logic, not arguing.

Compression is about the engine's ability to do work. The weaker compression is the less the engine is able to pull in air, compress it, light the gas, expel that energy into work.

When an engine operates in water or under load, there is resistance against the engine. A smaller amount when exhaust is submerged but not in gear.

When in gear, there is high amount of resistance and lack of compression in one or more cylinders will cause poor idle or it dying completely when in gear.

There is no compression fix in a can, only the proper repair/replacement of what failed and that costs thousands of dollars generally if it is found to be a mechanical issue and not a gasket issue.

 

[racerone]

I guess i missed all the battery / starter fixes in post #1.-----Not going to present my case.----Good luck sorting it out.

 

[brodmann]

I'd guess carburetor issues if it runs at high RPM's, but won't crank or idle.

 

[Mudbugger]

OK a bit of backgrounds, back stories and updates.
First the update, cold compression, wide open throttle plates, 115# across the board.
Second, back story on this engine: he bought the boat about 1 year ago. Ran great but would only run 10 MPH, found out only running on the left hand bank. No spark, new power pack didn't change anything, finally a new stator fixed it, spark on all 4 now.
Somewhere during all of this, they got 5" of rain, in about a 2 hour period, the boat was in the lake, the bilge pump got overwhelmed and the boat got swamped, powerhead tilted up, but the carbs got submerged.
Somewhere in that process, the starter started acting up, tried jumping, changed battery, paralleled 2 KNOWN good batteries, finally tore the starter down to find a broken brush. New starter fixed that.
Which is where we are now.
Background information, if anyone is interested, at this point. I've been an engine builder, for over 40 years, not just an assembler or a "parts puter togetherer" but I've also machined everything, other than grinding crankshafts and camshafts, but virtually all of that has been 4 cycle automotive, with 2 cycle experience limited to freshening piston port and rotary valve, motorcycle and snow machine engines.
That's my story, and I'm sticking to it!

 

[Scott Danforth]

Post the compression numbers

Low compression would be hard to start, however run-ish at higher rpms

 

[tphoyt]

He stated 115# on all.

 

[brodmann]

Buy carb kits and get to work. Watch a video or find a diagram of all the carb parts so you'll know where the idle circuit parts are. You'll need carb kits because you will have to remove some small lead plugs to clean out passages under them and the kits will have the replacement plugs.

 

[Mudbugger]

Buy carb kits and get to work. Watch a video or find a diagram of all the carb parts so you'll know where the idle circuit parts are. You'll need carb kits because you will have to remove some small lead plugs to clean out passages under them and the kits will have the replacement plugs.

I will ask him to get the kits, but by this time, he's pretty much sick of the whole deal. He already has another boat, which is better suited to his needs anyway.
Can you explain, why the carbs being dirty, would make starting in the water, much harder than starting while on muffs?
Again, looking for the logic and mechanics, behind it.

 

[Mudbugger]

Well the good news is, the problem has been resolved, at least for us.
He sold the boat today, even explaining the problems, the buyer didn't care, he didn't even want to hear the engine trying to be started.
All parties, INCLUDING me, are happy.
Thank you for the suggestions, even though this will haunt me, I will be happy to move on!