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Help, for a friend of course

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Hey all,

my buddies asked for help fixing his idle and throttle issue on his 2004 yz250f. Basically his bike stalls when given slight throttle unless its fully warmed up. Hes having all kinds of issues except at WOT.

I took the carb off cleaned it the best I could but I cannot for the life of me figure out his jetting. The PO must have not known a thing.. or maybe i dont. 

Heres what I gathered so far:

Leak Jet 90- 40 is stock

main jet 182- 178 stock

Needle 0BEKR- NHKR Stock (both in 4th clip position)

Here is where I get mixed up.. there are 2 jets on either side of the main jet when you take the bowl off. One of them is a 72 and its a super small piece and the other (I am assuming its the pilot jet) is a 38. We are in Western PA at the moment temps are 70-90 and humidity pretty high...

Here are my questions:

1) What is the 72 jet? 

2) Should I forget about messing with it and buy a kit that has all stock components? 

3) there is a black knob on the outside of the carb.. it adjusts where the throttle is positioned... What is the stock position on that? 

 

THANKS!- I HATE JETTING

 

 

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The 72 is the starter jet - 'Choke'- fuel enricher, it is fine.

Stoclk leak jet is a 90, a 40 is commonly used by non-pro racers for woods riding, it is fine.

Pilot jet could be a 38 though typical size is a 45 UNLESS... the bike has a crappy alloy (aluminum) fuel screw, then a 38 is not uncommon. I see you have the  stock fuel screw.

Main jet is too big unless the entire top of the air box was removed, it which case it is OK. Never any need to remove the entire top but people think if some is good, more is better. Five shots of bourbon=good, an entire fifth must be better.....

There is not 'stock setting' for the black knob, you set it for a idle speed appx. 1,850 rpm with a hot bike

 

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 fuel 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 knob 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 speed (knob) 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 fuel 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 1,850 rpm, but go by the spec in your manual.

 

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OK Williams thank you. By the grace of the bike gods i actually got it tuned in idling smoothly and the bog is much much less. Any opinions on the oring mod everyone keeps talking about?

 

Edited by bianco013

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9 hours ago, bianco013 said:

OK Williams thank you. By the grace of the bike gods i actually got it tuned in idling smoothly and the bog is much much less. Any opinions on the oring mod everyone keeps talking about?

 

Forgive my grubby fingers.

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