I'm stumped 1987 Yamaha 175

[Dave C]

I've had the same problem since January and can't figure it out. My engine will start missing intermittently not consistently while running over 3000rpms. This will come and go, I can run for 30 minutes just fine then it will start missing as it is doing it you can see the fuel spurt in all 3 carbs. I was sure it was fuel related and replaced all fuel lines, both fuel pumps, primer bulb, both fuel filters and rebuilt all 3 carbs. Still had the problem and noticed a head gasket leak, replace both, still does it. Can this be electronic, I didn't think so because it comes and goes. I'm just amazed it will run great then on the next take off run so poor. I would appreciate any suggestions.
thanks,
Dave

[skeeterlesssx200]

When it starts to mess up on the water, does it only do it in gear under load? Or will the engine not rev up in neutral?

[BuzzB8]

Hmmm, I'm not a mechanic and it seems like you've covered the bases with the fuel with the exception of the screen in the fuel tank. But, to me, it sounds like it could be electrical. Maybe something as simple as a ground wire not making good contact. Check all of the ground wires that bolt to the engine and check any that connect to the ignition coils.

[Dave C]

It seems to idle just fine and I don't notice any missing up to around 3000-3500 rpm's right about the time I get on plane. If it is missing prior I can't tell, also I have 2 fuel tanks and it does it on both. With the cowling off and the carbs exposed I can watch all 3 carbs spit or miss fuel at the same time while it is missing so now I'm just guessing that something electrical is cutting out at on an irregular basis.
I really appreciate your suggestions.


Modified by Dave C at 1:22 PM 11/13/2007

[Chris M]

Could be some water in the gas. After you get going it shakes up the fuel enough to get it in the carbs??