Yamaha 15hp 4 stroke early 2000s need advice?

[YammyGoneWrong]

Hello I am having issues with my 15hp 4 stroke 2002. Cleaned carbs, added new fuel tank and lines. Runs well enough (occasional miss?) when I start it under earmuffs but after a while (when it gets warm?) It will not idle, It will run at revs but if I let it idle it will start to sputter/miss/chokeup/ and eventually stall out with a puff of smoke out of the air filter...

Any advice appreciated

[TownsendsFJR1300]

Does squeezing the primer bulb help keep it running?

Sounds like the fuel pump may be leaking (would cause your "sputter/miss/choke up), and not pumping.
Being 20 years old, the diaphram may have failed:

https://www.boats.net/catalog/yamaha...0/f15elhy/fuel


There may be some other fuel issues, however I'd start there..

.

[99yam40]

to me back fire thru the carb on a 4 stroke means spark hits while an intake valve is open

[boscoe99]

My guess is that the carburetor needs some further cleaning. Particularly the idle circuit. Possibly the float adjusted.

A lean mixture due to a dirty carb restricting the flow of fuel can result in a back fire.

[YammyGoneWrong]

Hi Boscoe, what is the idle circuit?

[boscoe99]

It is the orifices and passageways through which gasoline and air pass and are mixed together to run the motor at idle and very low RPM's.

[YammyGoneWrong]

You're a legend mate I couldn't work out that top piece for the life of me. I'm guessing that's my problem because the rubber part is stretched and doesn't seat properly and also fuel seems to leak out of there occasionally. I will replace.

Do you have any tips for cleaning the carb? All I have done is remove the bowl, float, needle, the brass plug, pilot jet plug and emulsion tube/pilot jet. Then carb cleaner and pressured air.

I haven't pulled apart the plunger looking piece on the side of the carb. Could you tell me what this is? And what it does? It seems to only engage when in gear with full throttle.

[boscoe99]

You're a legend mate I couldn't work out that top piece for the life of me. I'm guessing that's my problem because the rubber part is stretched and doesn't seat properly and also fuel seems to leak out of there occasionally. I will replace.

Do you have any tips for cleaning the carb? All I have done is remove the bowl, float, needle, the brass plug, pilot jet plug and emulsion tube/pilot jet. Then carb cleaner and pressured air.

I haven't pulled apart the plunger looking piece on the side of the carb. Could you tell me what this is? And what it does? It seems to only engage when in gear with full throttle.

Without knowing what model of Yamaha four stroke 15 HP motor you have I am going to guess that it is the accelerator pump.