What should the stock carb jets be for a 94 yz250 with the stock pipe and aftermarket silencer

Depending on where exactly you are experiencing hesitation. The pilot jet will control idle and off idle transitions, from there the main jet will be responsible for fuel delivery at anything beyond 1/4 throttle openings.

Without looking at your carbs specifically my guess is that your issue would more likely be stuck slides or damaged diaphragms rather than dirty jets, so be sure to clean those and then check their operation with compressed air.

You haven't installed an aftermarket exhaust or a non-stock air filter have you? these can also cause the kind of problems you're having, and will require you set up the carb properly to be used with them.

Hey Anon,
Proper and correct jetting is something that can only be achieved in person by a REAL MECHANIC that KNOWS how to "read" a spark plug,,,With the mods you mentioned.. you need to know the stock jet sizes..a close guess would be reduce the main jet by two or three steps and lower the needle one clip position... oil mix should be at least 32:1....or better yet 28:1.. KEEP the oil mixture and jet the carb for performance....( I see TOO MANY IDIOTS that instead of jetting a carb correctly just reduce the oil ..some as low as 50:1(INSANE) just to keep from fouling plugs.).. then WONDER why their engine doesn't last long... hahaha????
YOU > BE SMART!!

1. vacuum leaks at the back side of the carb spigots or other vacuum lines off/broken. Remove the carbs and spigots from the head and clean with acetone/laquer thinner afterward sealing the spigots to the head with gasket maker/silicone rtv.
2. Carb idle and low speed jets may be plugged up and carbs need a correct cleaning.
3. Carbs need rejetting to match the after market mufflers. Take it to a shop with a motorcycle chassis dyno and they will be able to tune the after market pipes.

check tire pressure and make sure its not running rich

Hi there,

The jets are for increased performance but the jets installed must be in relation to the pipe used. An open pipe would require larger jets. If the jets came with the pipe when the previous owner purchased it, then it should work. My advise would be to tune it up, sync the carbs, and time the sparks.

If all else fail, ask the previous owner to provide the stock jets and replace it. Stock jets along with the stock pipe will almost always run the first time. Sync the carbs and tune timing. If you have it all running smooth, from there you can do upgrades like stage 1 jet kit or purchase a performance exhaust.

Please do let me know if any of this was helpful,
I'll follow it up should my suggestions fail,

your factory jets should be ok with stock carb and exhaust,unless it came from way down south or someone changed them.factory jets are main jet #380,pilot jet #30

The stock main jet is #350. As to fuel, it is best to run premium gas.

usually there are clamps which go aroung the silencer pipe.just undo pinch bolts and support brackets on silencer

You will see a lack of performance by removing the stock pipe and doing nothing else to counter the removal. Yes it will be much louder but it can also adversely affect everything in the motor from valving to spark plugs to a significant reduction in engine longevity. rather than outright removal have you looked into an aftermarket pipe? I agree that stock pipes can be a bit on the dull sounding side, but I would recommend staying away from drastic steps such as removing the whole can,,,