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1988 Yamaha 6 Cylinder misfire

S

skip40

New member
I have a 1988 150hp 6 cylinder that I think the bottom two cylinders are misfiring. The engine revs fine in neutral however, once you put the engine in the water under pressure, when you put it in forward it barely revs past 1700rpm. It has new coils, new spark plugs, I rebuilt the carbs last year. Any ideas what could be wrong?
 
I've posted this reply before as I zero in on one keystatement you made "I rebuilt the carbs last year". Did you do awinterization on that 2-stroke? Fog it and then pull the fuel feed whilerunning and let it burn all the fuel out of the system until it died? If not,welcome to Obamathol! This ethanol fuel crap we are stuck with is causingproblems everywhere. If you have compression and a hot spark in all cylinders,it is a fuel feed issue and your 1988 wasn't designed to tollerate Obamathol(E10). This ethanol crap may have started eating away at the insides of yourfuel lines throughout which causes that gummy crap to clog your carbs when itbreaks lose and upon the seasonal fire up and the fuel starts to flow again.Best bet (and I am no pro) would be to take that ****ty gas out of the tank andfeed it to your car that can deal with it. Find a station near you that sellsnon-ethanol gas and put that in the tank. Pull the carbs and flush out the fuelsystem by squeezing the fuel bulb with the fresh gas and maybe you can get ridof the crap that is probably in the fuel system. Squeze the bulb enough thatyou've pushed all that stale ethanol blended fuel out and taking with it thegum and mess that may be residing throughout the entire system. Put the carbsback in and pump up the bowls with that fresh gas and maybe you are good to goand can stop the mess this ethanol has made of your fuel lines. Non-ethanol gascosts a bit more if it is available in your area but it is worth the price oryou'll spend countless hours as a shade tree mechanic.
 
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