Flooding and fuel line pressure???

[Plan3]

Here is my situation with a carb-equipped 175 hp Yamaha: At idle speed the lower of 3 carbs floods badly. Brought to the attention of my mechanic, he informed me that he would replace my carbs with ones that came off a motor that was functioning. He did, but the flooding continues. If I race out the motor, the flooding stops. As soon as I drop it to low idle, it floods again. I've read somewhere on a couple of posts about the portable fuel tank bloating, and that the excessive pressure from this condition is what causes the flooding. So, I've backed off on the cap for the tank. Motor runs fairly OK this way at a moderate speed. Try to step up and the motor falters. (I'd like to be able to troll without flooding, and to be able to step up to get to my banks and to return home.) Can anyone suggest a fix?

 

[Propwash79]

I would start with rebuild the carbs if it's cheap. Sounds like the needle valves aren't seating correctly and then flooding the bowls when idling.also check the thread for fuel system testing. If you open the cap on the fuel tank and the proble still happens then I would rebuild the carbs with new needle valves and seats.

 

[Plan3]

Thanks, Propwash! I'll keep in mind your suggestion as I wait for other ideas. (I've explored the rebuild option and priced the kits. The mechanic who first attacked the problems of "hard starts," and flooding, did not really resolve either, came to my attention with several recommendations.He did not solve either problem; instead, he came back with 3 carbs that he said worked on another motor.Same results! But, thanks, anyway!)

 

[flyingscott]

It should be easy to find out if tank bloating is the problem stick it in the sun and see if it happens. What year is your motor do you have a choke plate in the carb or do you have an electric primer. I would look at either of those

 

[schematic]

if its a 2-stroke, its possible that a reed issue is causing blow back at low speeds mimicking a flood condition