Dropping top two cylinders intermittently?

pataterchip

Cadet
Joined
Dec 1, 2008
Messages
19
2001 60HP Bigfoot S/N#OT 294069P
I took it in to have the carburetors synced which was done. The shop doing the work has informed me that while the motor is idling and or revving the top two cylinders go off line or Miss from time to time but do come back. There is what he felt confident was engine oil coming out the thru prop exhaust but no water in the oil crank case and not enough oil to drain the oil level any detectable amount. He does not feel it is either carburetion or ignition related I am supposing because he told me he had diagnostic tools hooked to it and did not see a problem. The carbs were rebuilt because the motor would miss and try to stall at around 2500-3000 RPM but only under load at the lake not hooked to the hose. Any ideas?
 

Laddies

Banned
Joined
Sep 10, 2004
Messages
12,218
Re: Dropping top two cylinders intermittently?

It sounds like rev limiter if you engine is so equip, if not your losing a CDM unit.
 

mthieme

Captain
Joined
Oct 6, 2007
Messages
3,270
Re: Dropping top two cylinders intermittently?

Mercury did this by design.
Check out this thread - may or may not apply to you -
forums.iboats.com/showthread.php?t=286695
 

James R

Commander
Joined
Feb 1, 2007
Messages
2,664
Re: Dropping top two cylinders intermittently?

Apparently all the fuel is not being burnt. Could be running rich and swamping the plugs. Could be time for new plugs. Try switching the plugs around to see if that makes a difference. Of course there is the old possibility that the compressions are down. Then we come to the spark. This can be several things. Wires, coils,wiring,CDI, flywheel coils. It is unlikely that more than one spark coil has failed.
 
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