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Ok so what I have is an older but rebuilt straight-six 90hp two-stroke mercury marine engine with 3 carburetors and coil pack ignition. The problem is that when I give throttle it bogs down and runs weird.

Yesterday I put in some new plugs then idled for about an hour then gave it throttle, it ran great for almost 10 minuets, then we throttled down for a few minutes and it never worked like that again.

Few symptoms/conditions:

1. All cylinders have spark (ok).

2. All cylinders have equal compression (ok).

3. Timing (ok)

4. Oil to gas ratio is a little rich (for break-in period 25:1, reg = 50:1)

5. All carburetors seem to jet out gas (although crab #2 for cylinders 3 & 4 seems to be the weakest jet, maybe because cyl #4 isn't firing??).

6. Piston #4 is clean and shiny like it hasn't seen combustion; all other pistons have some carbon on them.

7. Idle doesn't change when I remove the plug's wire from cylinder #4.

8. "WEIRD" at night or in the dark when I run the engine I notice that spark plugs 3,4,5 & 6 glow a purplish bluish color around the porcelain neck (white part). Its not very bright but I saw it. Says to me that there's no voltage in the core of the plug, it's all around the outsides.

9. I removed all plugs, installed just plug #4 and spun the engine, engine popped and for only that one piston the combustion seemed strong. Same compared to when I did it for plug #1.


If any of you have ever seen these things please give your input. I need to get my boat runnin so I can go take some vacation!!!  

I know nothing about carburetors, but there are many people on this board who do, keep checking back I’m sure you'll have a knowledgeable answer soon.  

OK!! i think i got it! wasnt anything to do with ignition but i think that it was either carb #2 was dirty or the reeds wernt set right. i pulled off the carbs. blew out all holes with 150psi air, and while the carbs where out i fiddled with the reed valves. put the carbs back on and instantly i noticed the idel was different. looked further into it and all my symptoms had just dissapeared.

GREAT DAY!!!!!!!!  

glad i could help......haha