DT85 comp and spark, but won't run on bottom cyl.

[repodude]

acquired a center console with an older DT85 (white) and have good, solid compression on all 3 cylinders (less than 4lb variation) and good strong spark. It runs like a champ with the flush boot on. Put her in the water and it won't get out of her own way . Upon further digging, it appears to be the bottom cylinder and it just wont run on it. I am NO marine tech by any means, but have built my share of muscle cars so I rebuilt the bottom carb and still the same thing. Any suggestions or recommendation as to my next step would be greatly appreciated. Repo

 

[Gyrene]

Swap as much as you can with another cylinder - plug, plug wire, carb...1 item at a time to see why...

 

[99yam40]

good compression and good spark at the correct time are needed along with the correct amount of fuel to air ratio.
Too much or too little fuel will not allow cylinder to fire properly.

Spraying a fuel oil mix into carb while problem is happening should indicate if not getting enough fuel. not easy to remove fuel to test for too much.

Leaking fuel pump into crankcase pulse port can cause too much fuel to a cylinder .something to look for

 

[repodude]

Got it !!!! doop dee dooo, there was NO throttle sensor on this thing..... Timing ?? what timing.. issue #1 resolved

 

[99yam40]

spark timing is measure on these just like you do on automotive motors with a timing light.
You know what happens if it does not advance as it should if you played with automotive motors

 

[repodude]

Got that issue handled Vice Admiral 99yam40. Now what I am guessing is the "spark interrupt" is kicking in at 1/2 throttle. Reading different threads it appears the ICM is thinking it has low/no oil pressure and going into a safe mode. I boated yesterday for 5 hours with NO issues other than only able to go 1/2 throttle. The oil tank and sensors had been removed before I obtained this lovely piece and am trying to find a way to bypass this issue without buying whatever is missing on the injection. Running 50:1 now and have no problem doing so forward. Repo