300ex carb help

[TJN173]

I just jeted my stock 300ex carb from a 122 main jet to a 125 mian jet. I put a after market pipe and a procircut exhust on it so I decided to re jet, but there is no other motor work done. I also ajusted the needle one turn down on the carb so when you give it more throdel more gas is aloud in. The problem is when you give it full throdel it bogs down for some reason. The idel is fine but once you go to full throdel it backfires and bogs down to were I dont get full power...This is my first time working on this carb so any tips would be great, thanx for the help in advance.

[TJN173]

When I adjusted the jet needle clip I went from the standard 3rd position grove to the 4th position...Would this cause the problem moving it just once space?

[Sjorge450R]

yes moving it is going to cause this problem. Just move that needle setting back to were it belongs and your problem will be fixed.

To explain to you what you did.
You are making the carb give more gas to the engine when you punch the throattle. That little bit of gas is too much for the engine to burn.

Steve

[TJN173]

Ive put the clip back to the original position and it helped a little but there is still a problem because im still not getting full power. Would a higher jet fix the problem? Or would a air leak somewere be causing this?

[Sjorge450R]

explain the problem to me more. Is it only bogging when you first try to start moving? Does it run good when you are running at full throatle

I need more info.

[TJN173]

No it runs great at idel and half throdel then once you try to hit higher rpms at the top end of the gear it seems to backfire and sputter you cant get a full rev like you should.

[Sjorge450R]

sounds lean....change your main jet up one size.

[bwamos]

Aye, the needle has nothing to do with full throttle (ok maybe 1%, lol).

Go up to a 128 or 130 keihin main jet. If your bogging at a 125, I'd reccomend starting at 130.

Needle should be up one position (clip down) from stock. And turn the air screw in until it seats. Turn it out slowly (giving about 15 sec for the engine to catch up each movment), until the engine speed stops increasing. Then turn it back in a 1/2 turn.

If you're running aftermarket filter and no lid on the air box.. you'll probably need a 132.

Here's a good article on jetting a Keihin carb.
http://www.duncanracing.com/techfaq/Tech_keihin-carburetion-jetting.phtml

[8my_Cash]

i run a 128 with a k&n and no air box lid and its fine

[TJN173]

I havnet touched the carb in a weeks becasue it was so cold out last week and I dont have heat in my garage. But anyway, this week we messed around with it agian and tryed it with other carb off an 02 300ex and it had a 118 main jet and for some reason it ran great. I dont know were the needle is set in this carb but he was running a FMF head pipe and FMF exhust with a 118 main jet... I dont really understand why you would go backwards but it seemed to work for some reason...

[8my_Cash]

elevation might be a key part:)

[TJN173]

Well 118 is what its going to be at for the winter I guess.

[Sjorge450R]

Originally posted by TJN173
Well 118 is what its going to be at for the winter I guess.

i use a 116 dyno jet, if what you are talking about is a 118 dyno jet.

[hardkoratvmxr]

use a 128 that is what i use with a hmf slip on and k&n airfilter with no other mods is a 128 main jet and needle clip moved down