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Discussion Starter #1
Ive been trouble shooting on my excel.
It will start first pull...will idle fine for a bit and then the idle will slowly lower and die. You can keep it running by giving it throttle. It can rev up but does bog a little if you increase the throttle quickly.

I thought it was getting too much oil, because it does smoke a lot. I unhooked the 2 oil lines that go to the intake (did not remove the oil line to the oil pump) and ran mixed gas. still smoked really bad and did not run any different.

The plugs are certainly getting fouled. Now I am wondering if the carb is super rich.
I don't use the "starter" fuel enricher/choke when I start it.
If I give it choke when it is running the rpms drop.
since it has to have some throttle to stay running and dies off if you open the choke, it would seem that it gets too much fuel and not enough air.

I have checked the bowl float level and checked that the inlet needle closes. I cant find any info on proper float level, but using common sense I did adjust it some...which made no difference.

Other than the float level...and the 1 needle I can adjust, I don't see any way for the carb to be made to run leaner. It is not just running rich like it bogs, it runs so rich that you couldn't really drive it right now.
 

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Carbs are jetted for temperature and elevation. If it's warm out and the sled is jetted for cold weather, the air/fuel will be really rich.

What carb does the sled have? Most carbs have an idle mixture screw that you should be able to adjust to lean out the air/fuel...
 

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Discussion Starter #3
Carbs are jetted for temperature and elevation. If it's warm out and the sled is jetted for cold weather, the air/fuel will be really rich.

What carb does the sled have? Most carbs have an idle mixture screw that you should be able to adjust to lean out the air/fuel...
I will have to get the carb ID when it is light out.
It does have a screw to adjust...it makes little difference going 1 turn either way.
Ive had it running when it is 50 degrees outside.
Also, the previous owner said he was riding it last year...it fouled the plugs while riding and he put it in the shed and didn't touch it after that. To me that indicates something failed, broke or stopped working right.
 

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Check the diagrams here

1986 Yamaha EXCEL III (EC340K) Carburetor | Babbitts Yamaha Partshouse

That looks like a butterfly carb. The pilot screw controls the air to the pilot jet. If you turn it out or in and there is no change to the idle, the pilot jet or air or fuel passages to the pilot jet are probably clogged. I would start by removing the carb and giving it a good cleaning, paying particular attention to all the small holes and orifices in the carb. The spray carb cleaner may not be powerful enough to remove potential varnish buildup in the small passages, so you may have to poke into those with a soft wire (I use one strand of Cat-5 or telephone cord wire with the insulation on).

I've not torn into those type of carbs often, I had a couple of Enticers (79 and 80) with similar carbs, but they adjusted fine so I didn't pull 'em down.

The air screw meters air to the pilot jet. The screw makes the idle air/fuel mix richer when you turn it in (less air) and leaner when you turn it out (more air.) It would stand that the pilot jet is clogged if the idle is off and the plugs are fouled, which would indicate a clogged air passage (no air, lots of fuel.)

Good luck!
 

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Discussion Starter #5
Ok, ill check that. I have had the carb off and cleaned the jets that rest inside the bowl, but didn't remove that pilot screw or try to clean out it's passages.
 

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Discussion Starter #6
Check the diagrams here

1986 Yamaha EXCEL III (EC340K) Carburetor | Babbitts Yamaha Partshouse

That looks like a butterfly carb. The pilot screw controls the air to the pilot jet. If you turn it out or in and there is no change to the idle, the pilot jet or air or fuel passages to the pilot jet are probably clogged. I would start by removing the carb and giving it a good cleaning, paying particular attention to all the small holes and orifices in the carb. The spray carb cleaner may not be powerful enough to remove potential varnish buildup in the small passages, so you may have to poke into those with a soft wire (I use one strand of Cat-5 or telephone cord wire with the insulation on).

I've not torn into those type of carbs often, I had a couple of Enticers (79 and 80) with similar carbs, but they adjusted fine so I didn't pull 'em down.

The air screw meters air to the pilot jet. The screw makes the idle air/fuel mix richer when you turn it in (less air) and leaner when you turn it out (more air.) It would stand that the pilot jet is clogged if the idle is off and the plugs are fouled, which would indicate a clogged air passage (no air, lots of fuel.)

Good luck!
Had some interesting results today. I took that pilot jet out and sprayed carb cleaner down the hole. This had no effect. But as the idle was slowly dying I played with the pilot screw...first turning it way out and then I turned it all the way in. Once turned all the way in, the idle came back up! It idles very well, and the throttle response is much better (almost no bogging at all)
I let it idle and revved it up a few times (upto 7k) and had it running for 15 minutes no problem.

So, obviously that jet should not have to be closed. Having it closed must be compensating for a the real problem. I checked the plugs after running it for 15minutes... the coil side plug was still a bit wet but the other plug was dry and looked clean.

If that pilot screw controls air, then the machine was getting to much air...which I doubt.
If it controls fuel at idle, then I leaned out the mixture by closing it.
Either way, Im not comfortable driving it like this. for all I know it could be running lean at idle and be OK when I give it throttle...but that could be bad for the motor.

any ideas?
 

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It could be the action of removing the screw and spraying some cleaner in there, then screwing the screw back in dislodged some debris/varnish.

I would remove the pilot jet and make sure it's spotless. Screwing the air screw all the way in with little change usually indicates the pilot jet is too small or is clogged with varnish.

You can't get carbs too clean ;)
 
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