300ex need help jetting!!

[chargercalvin]

i just bought a 700dollar 99 300ex. it doesnt run right at all. it backfires really bad on deceleration and takes a long time to completely warm up. the throttle is a little hesitant in lower rpm's and i feel like it might be running hot??? so i guess this means its running lean?? i dont know if the previous owner put a jet kit on it. he should have because it has a fmf megamax pipe(the one with an end cap and plates) and a k&n filter with holes in the lid. im guessing he didnt rejet it and thats why its running like crap. i dont wanna pay the 50 bucks for a kit so i was just gonna buy a slow jet and a main jet. i was thinkin a 126-128 main and a 40 pilot?? i just want it to be a solid running bike, if the jetting is off a little bit it will be ok. any info will help guys

thanks,
calvin

[Tommy Warren]

you can buy individual jets for the 300ex at www.jetsrus.com and they come with a sticker:eek2: !

[JohnT_98300EX]

my 300 has 6 uni filters vents in the lid ,after market filter,and a pipe /muffler, (see signature) I went with 128 main as the only change. I have just a bit of hesitation 1//4 throttle (nothing to merit taking it all apart again) and decent running on top. I will goto a 130 when / if I have to take it apart again.
hot is almost always lean
as for the pilot jet it is my understanding that it is basically starting and idle. by the time you get "off idle" you are into the needle apart of the circuit

[Tommy Warren]

Originally posted by JohnT_98300EX
my 300 has 6 uni filters vents in the lid ,after market filter,and a pipe /muffler, (see signature) I went with 128 main as the only change. I have just a bit of hesitation 1//4 throttle (nothing to merit taking it all apart again) and decent running on top. I will goto a 130 when / if I have to take it apart again.
hot is almost always lean
as for the pilot jet it is my understanding that it is basically starting and idle. by the time you get "off idle" you are into the needle apart of the circuit

a bigger pilot will get rid of that 1/4 throttle hesitation the pilot controls fuel up until about half throttle and then your main will supply fuel from half to wide open throttle.

[JohnT_98300EX]

thanks tommy, you just helped me out for the upcoming build.
In another post I was wondering about whether to go with the 300 carb or the 400 I have. Both will need kits but I know what the 300 does pretty much.
So if I go with the 300 carb I will go up 1 size pilot, and from a 128 to a 130 or 132 main and see how that works.
The stumble in the 300 carb is past idle but less than about 1/4 throttle. It's not terrible, just don't try to stay at that exact RPM and it runs fine.

[chargercalvin]

i want to buy from jets r us. how do i know wich jets fit my carb. the table is a little confusing.

[Tommy Warren]

Originally posted by chargercalvin
i want to buy from jets r us. how do i know wich jets fit my carb. the table is a little confusing.

hey calvin,

your bike has a 32mm Keihin carb. all you do is go to the keihin carbs button on the left side. you have hex head jets. your stock ones are 122 main and 38 pilot. just to be sure I would ouder a 125, 128, and a 130 main. also i would get a 40 and 42 pilot. now chances are your going to use a 128 main and 40 pilot but if you have the other ones you can play around with them. and you won't have to wait days to get different sizes.

[chargercalvin]

ah ok thanks!