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Merc 90 2 stroke specific carb questions

S

Steve in sunny Fla

New member
Hi all, new to boats and this forum. Not new to engines and tuning. No 2 stroke experience. Quick learner though. Very good with carburetion. This is my first boat, I'm the second owner, and I'm undoing all the jacked up work from the previous owner, and learning all the way.

Specifics: 17" Stott Craft bay boat
2008 Merc 90 2 stroke ELPTO
130 psi / cyl
My questions are going to be specific, so please, no guessing.

Engine starts and idles fine within spec, Revs fine, runs great (now, not when I got it) . link and sync, ignition firing all cylinders, oil injection removed, fuel delivery proper. runs 36 mph, which is all I can expect from a 13.3x17 prop.

Question: The engine Idles on cyl 2 and 3; Cyl 1 comes on strong at about 1800 rpm. In studying the carb circuits, I see carb 1 has a factory drilled hole across the exterior vent channel to the channel with the idle fuel holes, as fed by the low speed fuel screw. I assume this hole leans out the circuit to stop from pulling fuel at idle to kill the cylinder. My questions is if I'm getting this correct, or should my engine be idling equally on each of 3 cylinders?

TIA

Steve
 
Flyingscott - not to my knowledge, though they had obviously been removed at one point.

Please clarify the purpose of the drilled hole under the cover of carb 1 that I referenced. Thanks.

Steve
 
Look at the carb does it have an idle circuit? put up a pic. Did someone swap carbs from a 4 cylinder thinking it would make more power?
 
It sounds like somebody put a 4 cylinder carb on your motor. The hole might be for lubing the cylinder when the carb is not working.
 
flyingscott said:
Look at the carb does it have an idle circuit? put up a pic. Did someone swap carbs from a 4 cylinder thinking it would make more power?
Click to expand...
Yes, it has an idle cicuit just like the other 2 carbs. Keep in mind that this is a 2008, there may have been a factory mod to kill cyl1 similar to what the 4 cyls have.
 
And If that piston is not idling due to no fuel it is on its way to a certain death. So you either have a 4 cylinder carb or a idle circuit well and truly plugged.
 
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