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jeff_1
08-17-2006, 11:44 AM
"I have a 1991 yamaha 150 outboard (V6). The motor was running well but then all of a sudden it would not go to full power. Normally the engine could turn 5200 RPM but now it will only get to 4300-4400 (depending on trim). I checked and replaced all spark plugs, when doing this I noticed that the plugs on the two middle cylinders appeared to be bone dry (not fouled or carboned up), all other plugs light brown. The engine has three two barrel carbs. I removed the middle carb that serves the two middle cylinders, it did not appear clogged but I disassembled and cleaned all of the ports/jets anyway. This did not help. I checked spark on all cylinders, all good. I ran a compression test on all cylinders (the cylinders with the dry plugs were at 105 PSI all others between 108 and 110 psi. Checked the reed valves, all tight, no cracks. Carb lnkages sincronized and all butterflies open fully. All carbs pull vacuum. I am stumped! The engine just does not seem to be able to rev up under load and the two middle plugs seem as though they are not seeing any fuel.The carb bowl does fill with gas. I checked the fuel pumps and they looked ok. I am going to check exhaust manaifold to see if there is any blockage, any other ideas welcome.

PS: Also changed the fuel filter.

Thanks."

justintime
09-30-2006, 11:37 PM
what about the fuel lone feeding the middle carbs or the return