Multiple Dead Cylinder Diagnosis Help

[checkyourmirrors]

I have the boat scheduled for service but being an obsessive compulsive Control Freak I am trying to get a grip on how big this problem is or what it is. I purchased the boat at 61 hours and have put 43 hours on it. I had an engine survey done and a 100 hour service done at the 61 hour mark. Below is everything I know and some could be related or unrelated.

2006 5.0L TKS Mercruiser with 104 Hours. Last Compression tests were at 61Hours and all were close to 185psi, engine rarely run in the 2000-2999 range per the computer. No overheating issues since 61 hours that I am aware of:

1) Cylinders 4, 6, & 5 have ZERO compression
2) Cylinders 4 & 5 have partially missing side electrode
3) Engine backfires at around 3,000 RPM if I can get it that high, ONLY when in gear
4) Engine will only start when given throttle (not in gear)
5) Rest of cylinders are slightly lower by ~20psi
6) Gear Lube Reservoir seems to have lost 1/3 fluid in 30 days/15 hours
7) Gas odor coming from carburetor

 

[Bt Doctur]

Re: Multiple Dead Cylinder Diagnosis Help

1 recheck compression with carb wide open, recheck with oil added
2 run lean condition, too hot a plug
3 would backfire with bad plugs
4 most need the throttle advanved a bit to start
5 could be lack of oil on the cylinder walls
6 you have a leak
7 fuel pressure. fuel level, bad gasket, ethanol related