Please look at my Yamaha plugs

[boscoe99]

Is it now missing at idle at all engine temperatures - from cold until it gets hot?

Does it ever sneeze whenever it is idling?

Is it missing with the choke plate closed or with the choke plate open?

Have you checked the idle mixture setting screw?

If the plugs were clean and tan after the motor was being run at power, with no problems, but then the plugs get black and wet after the motor idles for a period of time, and the miss starts, I would focus on the idle mixture setting.

At what altitude are you?

[robert graham]

Did you ever check your fuel pump?....

[99yam40]

Fuel pump could be leaking into crank case though pulse port and cause too rich of a mix at low speeds, but not affect it as much under higher RPM. Something simple to check like Robert said

[yammie15]

Well always misses badly when the engine is cold. But still starts with choke, a bit of gas and one or two pulls. I knock the choke lever back in immediately, or it will stall. If I turn the gas down to idle before the engine warms a little, it will "chuff" two or three times, backfiring, but I don't know if it's through the exhaust or carb.

The first run of the day, 1/4-mile to the town dock, my heart is in my mouth. I always make it, but it is missing terribly but gets better as I throttle up past 1/4 as indicated on the bars on the grip.

When I come back to the dingy, after perhaps three hours in town, the engine starts right up without choke... one pull! The missing is still there but not nearly as bad, especially if I'm above 1/4 throttle. Some days, it sounds normal.

I looked at the fuel pump but didn't see two bolts that hold it in place. There is a cover plate with four screws. Maybe the bolts are underneath the cover plate?

The idle mixture setting screw is the one under the brass plug? No, have done nothing with that yet. Take it out and clean it, right? Then squirt carb cleaner in the hole before re-assembly?

I'm in the Caribbean... sea level! (And warm!)

Tonight, I will run it in the dark without the cowling and look for any pyrotechnics.

Thanks all... can't believe the support! Truly great!

Best,
Bry

[TownsendsFJR1300]

Can you list the year again and the specific model # for the engine please?

Just for looking up parts fisch's, (to find and post a pic of the fuel pump itself).

[99yam40]

Engine is a 2009 two stroke, Yamaha 15MSH. Model #684KS1057789. can I check the fuel pump myself?
Bry

Dang someone is getting lazy or just does not want to look back one page.

Pump is on the carb, but it should still get a pulse from crankcase,
And probably from the lower cylinder, but I am not positive

Compression could be down on that cylinder , who know until testing is done

[TownsendsFJR1300]

Dang someone is getting lazy or just does not want to look back one page.

I glanced back and didn't see the model, CHILL...

Is part #29 the fuel pump?
http://www.boats.net/parts/search/Ya...TOR/parts.html

[99yam40]

Is part #29 the fuel pump?

Yep that is pump body, wounder why they do not list the whole pump, only parts

[TownsendsFJR1300]

Yep that is pump body, wounder why they do not list the whole pump, only parts

Yep, it doesn't show (probably the picture angle) any nipple for a vaccum hose to the cranckcase.

Looks like parts (diaphram(s)) #28 and #30 may be the issue..

[yammie15]

Engine is a 2009 two stroke, Yamaha 15MSH. Model #684KS1057789.

I took a nice pix of my fuel pump, but for some reason can't up load it to the thread!

Had an interesting development on the way back to the sailboat last night. Half way there, with the engine running pretty well, I though, there was a sudden increase in RPM and we took off, singing!

I though that maybe a sticky piston ring had finally loosened up and my problem was solved. But this morning: still missing on start up.

And no arcing during a night run.

Thanx all...
Bry

[TownsendsFJR1300]

Thanks for the update.

Did you see the link in post #22, it shows the carb and fuel pump/diaphram integrated into it.

You probably need to look at those diaphrams for any holes..

[yammie15]

Yes, I saw the link and it looks like my fuel pump. (Still can't up load my photograph!) I'll remove the cover plate but then, will squeezing the prime bulb tell me if I have a faulty diaphragm? Or do I need to disassemble the pump and look for tears or holes?
Thank you,
Bry

[TownsendsFJR1300]

You should see if the diaphram is bad. Pumping the primer bulb with the assembly apart will just put fuel all over the place. It should come apart easily.

What's possibly happening (if this is the issue), is the diapham has a small leak.

Fuel gets sucked into the crankcase (due to the faulty diaphram) and thus extra fuel to the cylinder resulting in a fouled spark plug, crappy running, etc..

[yammie15]

Diaphrams are good! Damn!

I guess I'm going to have to drill out that brass cover over the Idle Screw. No electric drill but I guess I can get it with my hand drill, a screw and a set of vice-grips!

When I get it out, I'll need instructions as to adjustment of the carb.

Thanx all...

Bry

[TownsendsFJR1300]

Agreed, dang...

If your going to adjust/check that screw(I don't think that's the issue), once the cap is off, RECORD THE # OF TURNS IN to LIGHTLY SEAT the screw.

Write it on the garage wall/owners manual, etc.