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Jetting Question? New A/F Screw problems...


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Hey guys, I haven't actually ridden my bike at all this year with my busy work schedule, but I bought an hour meter the other day and decided to put it on. The meter isnt working with 4 wraps around the coil but thats not what im concerned about atm.

All I've done since last year was replace the leak jet with a #50 and put in an adjustable fuel screw. Ive done nothing else but check the valves.

I cannot for the life of me get the bike to idle with the choke off now.

It will start with the choke on after about 3-4 kicks and warm up (doesn't seem to idle down like it used to where I knew it was time to turn off the choke though). Last year it started with 1 kick almost every time.

Every time I turn the choke off when the radiators are nice and hot and I know the bike should be ready to idle, it will bog down and die. If I turn the choke back on, it will restart with one kick. When I turn the choke off, it will stumble/pop when revving, and when slipped into gear it will stall after a few feet of taking off.

The idle screw is set like its always been, and the fuel screw is set to two turns out from tight.

Is there something im missing like its time for a jet change somewhere? Its the same temp now that it was like last year and I'm at the same elevation.

Ive noticed this happening since I put in that dang fuel screw, but Ive tried all kinds of combinations of turns. I even put in a merge racing fuel screw spring to make it nice and tight.

I dont understand why it ran fine last year (I only put about 5 hours on it, if that) and I change the leak jet and fuel screw to get rid of the bog and popping on decel and it does this...

I really don't want to buy a JD Jet kit If I don't have to, and Im hesitant about letting a dealer screw me over on cash for something stupid like a simple jet.

Any advice?

Steve

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Do what brett says, buy a new pilot jet. If that fails to resolve it....

Not all fuel screws are created equal. Is it an alloy screw? They are often poorly made. Are you sure only one oring is in the carb? Not uncommon for it to stick up there, the owner thinks it is missing and a new one, only to have two orings....

Do the following:

Fuel Screw/Pilot Jet

Fuel screw settings in the 'book' are recommended starting points. Every bike is different, as is the temp and altitude. Set the screw according to this method. Do it with the bike fully heated up.

Gently turn the screw all the way in. Now back it out two turns. Start the bike and fully warm it up, go for a 10 minute ride. Set the idle to speed to 1,500~1,800 RPM as best you can (I know, without a tach this is tough, just set it to were it idles relatively smoothly). Once warmed, slow the idle to the lowest possible speed.

*** When turning the fuel screw, keep an accurate 'count' of the amount you are turning it and record it in case you have to reset it for some reason. Makes life easier when you can just set it from notes Vs. going through the procedure again.***

Turn the screw in until the idle becomes rough or the bike stalls.

if it stalled, open the screw about 1/4 more turn. Restart it and slowly screw it in till you can just perceive a change.

If the screw can be turned all the way in and the bike still idles perfectly and does not stall, then you need to go down a size in pilot jet.

Now very slowly, open the fuel screw till the idle is smooth. Blip the throttle, let the bike return to an idle, wait say ten seconds. Confirm it is the same smooth idle.

If the screw has to be opened more than 3 turns to get a smooth idle, you need to go up a size in pilot jet.

If you find it does not stall with the larger jet but has to be open more than three turns with the smaller pilot jet, put the larger one in and set the fuel screw at 1/2 turn.

If the idle speed increased, adjust the idle speed knob to return the bike to a real slow idle speed. You must then re-visit the fuel screw. Keep doing this till the fuel screw is opened just enough to provide a nice steady idle at the lowest possible RPM. Once this is done, increase the idle speed to the normal one for your bike, typically about 1,800 rpm, but go by the spec in your manual.

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Its an outlaw racing brand screw. As for the possibilty of an o ring stuck up there, I was the one who took the stock screw out and put in the new adjustable one so the o ring should be good.

Do what brett says, buy a new pilot jet. If that fails to resolve it....

Not all fuel screws are created equal. Is it an alloy screw? They are often poorly made. Are you sure only one oring is in the carb? Not uncommon for it to stick up there, the owner thinks it is missing and a new one, only to have two orings....

Do the following:

Fuel Screw/Pilot Jet

Fuel screw settings in the 'book' are recommended starting points. Every bike is different, as is the temp and altitude. Set the screw according to this method. Do it with the bike fully heated up.

Gently turn the screw all the way in. Now back it out two turns. Start the bike and fully warm it up, go for a 10 minute ride. Set the idle to speed to 1,500~1,800 RPM as best you can (I know, without a tach this is tough, just set it to were it idles relatively smoothly). Once warmed, slow the idle to the lowest possible speed.

*** When turning the fuel screw, keep an accurate 'count' of the amount you are turning it and record it in case you have to reset it for some reason. Makes life easier when you can just set it from notes Vs. going through the procedure again.***

Turn the screw in until the idle becomes rough or the bike stalls.

if it stalled, open the screw about 1/4 more turn. Restart it and slowly screw it in till you can just perceive a change.

If the screw can be turned all the way in and the bike still idles perfectly and does not stall, then you need to go down a size in pilot jet.

Now very slowly, open the fuel screw till the idle is smooth. Blip the throttle, let the bike return to an idle, wait say ten seconds. Confirm it is the same smooth idle.

If the screw has to be opened more than 3 turns to get a smooth idle, you need to go up a size in pilot jet.

If you find it does not stall with the larger jet but has to be open more than three turns with the smaller pilot jet, put the larger one in and set the fuel screw at 1/2 turn.

If the idle speed increased, adjust the idle speed knob to return the bike to a real slow idle speed. You must then re-visit the fuel screw. Keep doing this till the fuel screw is opened just enough to provide a nice steady idle at the lowest possible RPM. Once this is done, increase the idle speed to the normal one for your bike, typically about 1,800 rpm, but go by the spec in your manual.

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Yeah, those are re-packged ZipTy alloy screws.

Decel popping is a fact of life with a properly jetted YZ. They are race bikes, no play bikes. You can richen jeting to reduce or eliminate it at the expense of rideability and performance.

Leak jet is part of the AP and only affects acceleration

Fuel screw is for idle only.

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I understand about the popping, its not a big deal. I actually put that screw in back in December because I thought I would be taking it out in the cold and wanted to adjust it accordingly. I thought maybe the popping could be minimized thats all

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When is the last time you put fresh 94 octane gas in it?

September of 09. That was the last time I actually got to ride the bike.

See it sucks for my situation, im just a trail rider and I have only been riding at my 40 acre property up in northern michigan, I only get a few chances a summer to go up there. I have yet to even go there this summer whatsoever.

I cant exactly make a few adjustments and take the bike out, the bike is at my house in the suburbs of southern michigan right now...nowhere to ride and make adjustments. ­čśĆ Its hard to find people in my area who are out messing around on bikes...

When I get a chance I think I might make a video using my GoPro POV Cam and show you guys what its doing.

Steve

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