Low RPM, Vibration

[Jamepc]

I have a 2001 Islandia, 240 Merc EFI. The RPM's won't go above 4900-5000 RPM's. I did a compression check and all were around 130 psi. Next, I would like to verify all cylinders are firing. What's the easiest way to do this? If 1 or more aren't running, how do I tell which ones? Any other ideas or suggestions regarding this problem are appreciated.
Also at idle to about 1500 RPM's the engine is extremely rough. Very shaky like a cam with a lot of overlap in a car. So if all the cylinders are firing, maybe something else is off balance like a bad impeller? Would this also slow the engine and boat down?
Thanks,
James

 

[Jamepc]

Re: Low RPM, Vibration

Any ideas?

Thanks.

 

[Texasmark]

Re: Low RPM, Vibration

Might try a decarb then maybe a cleanout of the carbs. Sounds like all the carbs might not be fueling together.

I think I have checked ignition with a neon bulb (NE-2 Radio Shack) placed right on (against) the sparkplug wire. The high voltage ignites the gas in the bulb and you can see it glow.....no glow no spark....needs to be dark to work best.

Mark

 

[Jamepc]

Re: Low RPM, Vibration

Also, how should spark plugs look in this 2 stroke. They always have a black film of oil on them but that normal, correct?