yz 250 jetting

[mcraig79]

Ok thanks guys...got another question for yall...the One YZ i got which set for bout 3 yrs has major carb problems that cant be fixed without another carb.
The yz i got the other day for parts is between 94-96 same carb but jets are different. The carb i had i belive has a 175 and a 45 with a procircuit works pipe.
this bike i got for parts has a procircut platnium pipe and the jets are 170 and 48....which setup would i be better off with? I will be putting the other pro circuit pipe on my bike.

 

[BSWIFT]

http://www.dirtrider.net/forums3/showthread.php?t=42618
Read this thread and ride the bike. Determine what jets you need by following the proceedure. Takes several hours and a few plugs and jets but you'll get it dialed in. I printed out the guide and followed it to the letter. Got my YZ dialed in perfect for 68 degree temps. A bit rich in the heat and slightly lean in the cold but rips!

 

[whenfoxforks-ruled]

As long as the other carb is the same shape, and size, put your stock jetting in for your altitude, temperature, and engine. Do not go for a 100 mile trip, till you check the jetting. Even if it is really lean, a minute should tell how its running on each circuit/throttle opening, and not cause further problems, other than fouling a plug. Odd noises like detonation needs to be addressed asap! Any questions, yank your plug and read it. Jetting adjustments do not make sense, you may have other issues elsewhere. You can not jet an engine with issues.

 

[BSWIFT]

As long as the other carb is the same shape, and size, put your stock jetting in for your altitude, temperature, and engine. Do not go for a 100 mile trip, till you check the jetting. Even if it is really lean, a minute should tell how its running on each circuit/throttle opening, and not cause further problems, other than fouling a plug. Odd noises like detonation needs to be addressed asap! Any questions, yank your plug and read it. Jetting adjustments do not make sense, you may have other issues elsewhere. You can not jet an engine with issues.

That's an excellent point. Jetting is really not that difficult just a bit time consuming when you go thru the steps. Once it is right, your bike will run good. Be sure to inspect your reeds and have a clean and properly oiled filter in place when you start your jetting.
BTW, where are you located? Your elevation and normal humidity and temperature affect your baseline. If you get to the point you that you have the overall jetting right but you have some throttle positions that are just not as crisp as you like, you can look into different needles. At that point, contact JD Jetting and those folks will hook you up.

 

[mcraig79]

i am located near knoxville tn, i took the bike out other day and ran it...and must say overall done excellent...pulled plug and it was just a hair lighter then the coco brown color i usually aim for.
But at that time i was running 40:1 the guy who used to own it wasnt sure if he ran that or 32:1
if i am not mistaking in all my bikes in past i ran 32:1...i used to ride alot all way up to a CR500 but got out of it for over 10 yrs..now i am back into it and it feels good :D

 

[BSWIFT]

Your oil/gas ratio should not determine if the you are jetted rich/lean. This topic has been covered many times. The manufacturer recommends 32:1 with Yamalube. If the mix oil that you are using is rated for 40:1 or 50:1, run what you are comfortable with. I've run 40:1 in all my two strokes and only cratered a piston on a very cold day with a bad decision.
At 32:1, you will have more air to fuel ration that at 50:1 but it is probably not noticable except for the top riders and mechanics. Best bet is to use the same oil every time at the same ratio with the same fuel. If you intend to use race fuel, you will get the most consistancy in your premix and your jetting will be able to be cleaned up really, really well. If your using pump fuel (like me) use a good grade and the highest octane you can get consistantly. Not the choice of the pros but you'll get reasonably good results.