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290 fuel screw adjustments


fur_pig
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I just bought a used 06 Sherco 290 and am going over the bike inspecting everything. I pulled the carb apart and cleaned all the jets and made sure they weren't clogged. I put the bike back together and the bike runs really lean. The large screw on the carb that is supposed to adjust the idle actually seems to lean the bike out the more I turn it in. The RPMs will start to race high and it pings really lean. I found a happy place for it and have the air/fuel screw next to it 5 full turns out. This seems excessive and I feel like by turning it this far out (richening it up) I am compensating for a lean condition.

-What is a normal setting for the air/fuel screw? (how many turns out)?

-Why does my idle screw seem to be messing with my air fuel ratio as well?

I don't know enough about this bike since I just bought it to know if it has been running this way for a long time or what. The plug looks good and I sprayed all over the carb, intake, etc. with carb cleaner to listen for an RPM range indicating a vacuum leak but none were found.

I don't have jet numbers but can take the carb back apart tomorrow if need be.

Thanks for your guys expertise!!

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I just bought a used 06 Sherco 290 and am going over the bike inspecting everything. I pulled the carb apart and cleaned all the jets and made sure they weren't clogged. I put the bike back together and the bike runs really lean. The large screw on the carb that is supposed to adjust the idle actually seems to lean the bike out the more I turn it in. The RPMs will start to race high and it pings really lean. I found a happy place for it and have the air/fuel screw next to it 5 full turns out. This seems excessive and I feel like by turning it this far out (richening it up) I am compensating for a lean condition.

-What is a normal setting for the air/fuel screw? (how many turns out)?

-Why does my idle screw seem to be messing with my air fuel ratio as well?

I don't know enough about this bike since I just bought it to know if it has been running this way for a long time or what. The plug looks good and I sprayed all over the carb, intake, etc. with carb cleaner to listen for an RPM range indicating a vacuum leak but none were found.

I don't have jet numbers but can take the carb back apart tomorrow if need be.

Thanks for your guys expertise!!

Hopefully you got your pilot jet clean, but I think this more related to the fact your crank seals are shot and sucking air so it is lean and you are unable to compensate.

Also hope you took note of the pilot jet number, as I think you need to get it in the 36 range or better on our crap fuel.

I will add other comments in your other thread re- the crank seals.

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Hopefully you got your pilot jet clean, but I think this more related to the fact your crank seals are shot and sucking air so it is lean and you are unable to compensate.

Also hope you took note of the pilot jet number, as I think you need to get it in the 36 range or better on our crap fuel.

I will add other comments in your other thread re- the crank seals.

The pilot jet is clean and when I sprayed carb cleaner all around the engine cases, carb, air boot etc, I had no change in idle so I ruled out a "vacuum leak".

How many turns out should my air/fuel screw be?

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The pilot jet is clean and when I sprayed carb cleaner all around the engine cases, carb, air boot etc, I had no change in idle so I ruled out a "vacuum leak".

How many turns out should my air/fuel screw be?

Hi

I would ensure the small airway from the back of the carb is clear. This feeds the pilot jet.

Blow out with air from front of carb backwards through syatem.

The mixture at partial throttle relies on the pilot system operating.

Because you are having to turn in the slow speed screw and the macine is running lean I would certainly check the pilot system.

Geebee

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Hi

I would ensure the small airway from the back of the carb is clear. This feeds the pilot jet.

Blow out with air from front of carb backwards through syatem.

The mixture at partial throttle relies on the pilot system operating.

Because you are having to turn in the slow speed screw and the macine is running lean I would certainly check the pilot system.

Geebee

I went through the entire carb again. It has a 35 pilot and 120 main...is this stock? Upon reassembly and test riding, it seems to be running pretty well but a tad on the lean side. I still don't understand why the air screw has to be 5 turns out for this thing to run right. How many turns out are you guys running?

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I went through the entire carb again. It has a 35 pilot and 120 main...is this stock? Upon reassembly and test riding, it seems to be running pretty well but a tad on the lean side. I still don't understand why the air screw has to be 5 turns out for this thing to run right. How many turns out are you guys running?

OK, well first thing to verify is the fact you do indeed have the stock dellorto on it.

I do not disagree with Ryan on this, as I stated you just gotta ride it a bit to see what it does, yet at the same time, your initial indications were not good, and we have replaced crank seals on newer bikes for symptoms related and being unstable..

The things seem to have a propensity to go a bit lean off idle anyway, which is why I have had to go up to a 38 pilot in the past. But on your base idle, at 5 turns out you are out of range of the screw to begin with. Look at the end of the screw and count the threads per inch, you are just at wide open past about 3.5 turns anyway! Fuel screw it is!

All this varies a bit bike to bike,

Another little trick would be to put the crankcase vent tube to your tounge to see if you can detect any changes in vacume when revving the bike. You can add a clear hose and add this to a water table test in a cup. Leckage measured in inches of water on the clutch side.

All fod for thought! :thumbup:

Edited by copemech
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