Puzzling idle issue on 6 HP yammy

[Yamadoggie]

Good compression. Good spark, Cleaned fuel filter and lines and tank. Carb disassembled, soaked and new parts kit put in it. Removed high speed tubes, idle valve before soaking. Not really dirty, just the usual carb cleaning job.

Motor starts on the second pull with choke. It will idle low until it burns up the fuel from the choke then will not idle below about 2500 RPM. Sounds like a blockage in the idle circuit right? took the carb back apart, ran a wire through all passages, resoaked and cleaned. Same problem. Not spitting out the carb at all, good suction at the throat. Still wont idle below 2500 rpm.

the idle mixture screw doesn't have any impact whether completely closed or open 5 turns.

Was looking for crankcase leak but nothing obvious. Clean motor. disconnected the kill switch as well.

Open to ideas please? worked on many many two stroke carbs before but never had one like this I could not fix.

[boscoe99]

Need a complete model identity. Two stroke, four stroke, production date, etc..

[Yamadoggie]

1980 6 HP, single cylinder 2 stroke.

[99yam40]

1980 6 HP, single cylinder 2 stroke.

I am sure that is not what is written on the motors tag

Are you outside of the US?
Yamaha did not sell here back in 1980

[Yamadoggie]

model # 6EO

[boscoe99]

An oldy but good. Not offered here in the USA.

Not sure what is meant by "It will idle low until it burns up the fuel from the choke".

There is no fuel in the choke. The motor is running on the fuel that is in the carburetor bowl. The choke plate being closed causes a greater amount of gasoline to be introduced into the carburetor when the choke is activated but additional gasoline should continue to be supplied to the carburetor bowl by the fuel pump as long as there is gasoline in the gasoline tank.

If and when the motor is hot, the choke plate is open, the carburetor bowl is fuel of gasoline, but the motor won't idle, then I am suspecting something is clogged within the idle circuit of the carburetor. If you spritz a bit of gasoline into the inlet of the carburetor and it will then idle, I further suspect that something is amiss within the carburetor.

Was the carburetor cleaned in a heated ultrasonic cleaner using a good brand of carb cleaner? If not, you might want to try that. Some passages are internal to the carburetor and difficult to get to.

[Yamadoggie]

when you chokei t it draws fuel into the throat as you know. I know there is no fuel in the choke. once that small amount of fuel is burned, it will not idle unless you crank up the throttle to about 2500 RPM, drawing off the hi speed tube and jet .

[TownsendsFJR1300]

You posted " idle valve" in your first post(removed it before soaking).

Is that the "idle jet"? If it's something different, the idle jet has to come out, not just a soak. If you can't see light thru it, it isn't clean...

Also, some jets have VERY SMALL holes drilled horizontal to the jet(ie, a fine wire pushed thru won't clean those holes out)

Where the idle jet screws into and with the air idle adjustment screw(that doesn't seem to do anything), I would be concentrating on those orifices.

Something is still clogged in there. Carb cleaner and an air compressor should help clean it out.

BTW, what are you soaking the carb in?

[Yamadoggie]

carburetor cleaner. and everything gets blown out with high pressure air.

[TownsendsFJR1300]

Ok, good..

Did ALL the jets get pulled?

[boscoe99]

I have been sitting here contemplating life and my navel and for the life of me I cannot understand why it quits running after a while with the choke applied.

[Yamadoggie]

when I start it with the choke ON, it starts right away . I turn the choke off and it will run for 2-4 seconds at a low idle. it will then die unless I open the throttle up to let it pull from the hi speed jet and main pick up tube in the center of the carb venture.

If I choke it again and then turn the choke off, it will again idle low for a few seconds.

everything points to a blocked low idle passage. Every part that could be removed WAS prior to soaking overnight and blowing clean. Every passage that could have a wire put through them was cleaned that way.

Only thing left is to pull the two lead plugs that seal up several internal passageways .

[TownsendsFJR1300]

I gather you soaked in sort of carb cleaning solution? (chem dip, etc?)

Also, if you hold the choke partially on, I gather it'll idle (not fully normal but in the ball park of normal idle RPM's)?