30hp Yamaha fuel problems??

mpsyamaha

Chief Petty Officer
Joined
Jun 8, 2007
Messages
400
i have a 97 yamaha 30mshv thats been giving me problems. i am no dummy to working on outboards but i just cant figure this one out. it seems to not be able to maintain fuel pressure. i have to keep pumping the primer ball in order to make it run right. when idling it will slowly get lean, give a few lean pops and then die over the course of about 2 mins. if i periodically pump the ball up it will keep idling. under WOT i have to pump the ball almost constantly to keep the rpms up. the fuel pump is brand new. new diaphragms and main body. all fuel lines on the engine are brand new. carbs just cleaned. tried switching between two different gas tanks, that had no effect. the fuel filter is also brand new, nice clear yamaha factory filter. i dont see any air bubbles in the filter. there is no fuel blowing back out the carbs. there dont appear to be any air leaks on the exterior of the carbs or intake area (sprayed with carb cleaner at idle and WOT and it did not affect rpms at all). so what the hell is it??? i have already bought a good bit of parts (as mentioned above) and tried everything i could think of. i somewhat suspect the fuel line from the tank to the engine, although it is less than a year old. it is not yamaha brand, i think i bought it at bass pro shops. anyone have any suggestions/ideas??? thanks
 

JB

Honorary Moderator Emeritus
Joined
Mar 25, 2001
Messages
45,907
Re: 30hp Yamaha fuel problems??

It seems pretty clear that the carbs aren't getting fuel as fast as you are burning it, MPS.

It seems that you have eliminated the tank and fuel pump.

I suspect that your fuel line has an air leak at one of the fittings or a leaky o-ring in one of the fittings.
 

randy_252

Seaman Apprentice
Joined
Jun 9, 2006
Messages
35
Re: 30hp Yamaha fuel problems??

I agree with JB. Tell you what. Take the fuel bulb and point the arrow to the sky. Pump it up, it should hold "tight" If it doens't you have hose bulb problems. Have it hooked to ur motor.

If you have to keep pumping it. Take the top off your motor and see which carb is leaking the gas out. The float is not sealing off. Notice any fuel stains running down your motor or rainbows on the water?

You can unhook all the carbs and make sure the float move freely
OR:

unscrew the drain screw...careful not to drop it...lol. run u a slim stainless steel wire up and jiggel that float. BE GENTAL.

you will feel like a monkey doing this but once i got the hang of it its easy.
 
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