jetting question
- Thread starter freeh
- Start date
MarctheSharc
PR Founding Father
I'd check for an air leak around the header pipe.
BriarcliffMx
PR Founding Father
like Marc said, get a new exhaust gasket, make sure the nut/bolt are tight. If no leak, then it might be lean at the pilot/fuel screw. How many turns out is the fuel screw?
TwentyThreeMX
PR Founding Father
bigger main helped when my 06 yz450f was doing that after i put an fmf system on it.
freeh
PR Founding Father
The bike has about 3 hours on it and it had the same problem with the stock exhaust when it had one hour on it. I will check the header bolts though. I doubt it is the gasket. Is it generally a lean condition that causes the popping? I went larger on the main per the Dr. D recommendations. I will adjust the air screw next time and see what happens. I could go larger on the main again.
Thanks for the input.
Thanks for the input.
TwentyThreeMX
PR Founding Father
sucking in air will cause it to run lean, double check the screws that hold the boot onto the carb too... maybe didnt tighten all the way down after loosening to move the carb to adjust the main? worth a shot....
from what ive seen the popping is when its lean, yes.
from what ive seen the popping is when its lean, yes.
MX724
PR Addict
There is no "air screw." Its really a fuel screw. Air screw is on the 2 stroke carbs. Usually I just back that out 1 turn or 2 to richen it. If it requires more then that then you probably need to up the pilot or the main. Be careful as to how much you back the fuel screw off because they can easily fall out of the bottom of the carb and the bike will run like crap. The fuel screw is the one under the bowl. Like i said if you have to turn it more then 3 full turns out from fully seated then odds are your jetting is too lean and needs to be adjusted. I'd actually start with the pilot and needle before chainging the main again. One step at a time. One jet at a time. The more variables you create the harder it will be. Make a change note it and if it doesnt work go back to your starting point and try again.
TCracing
PR Addict
Sound advice from all posts.
I would carefully turn the pilot screw in (clockwise) counting the number of turns to see where it is at. Turn back out to the initial setting and then increase (turn out) by about 1/4 turn then test and continue until desired results, or like someone else mentioned, until you get up to 3 turns out. Then its time to get the next size larger jet.
Also the comments about the exhaust are true, can cause deceleration pop. Also if you have an intake leak, this can cause all kinds of fits.
As MX724 stated above this is a fuel adjustment not air. General rule of thumb. If the Screw is on the engine side of the carb it is a fuel adjustment (turn out richer turn in leaner), If the screw is on the filter side of the carb it is an air adjustment, and Opposite results (turn out, get more air, leaner turn in, less air, richer)
You may try LOWERING the CLIP on the main jet as you may have an overall lean condition (this will raise the jet in relation to the slide) and richen the overall fuel mixture. This would most likely be the casee if you are getting the popping but still have good bottom end response (no hesitation or bog)
If you know someone who can reed a spark plug this would be the best place to start and eliminate some of the guess work. HOPE ALL GOES WELL. GOOD LUCK.
PS. If you already installed a larger main you may run too rich, poor overall response, especially when temps climb you may need to raise the clip on the main jet to lean it out a little / just FYI.
I would carefully turn the pilot screw in (clockwise) counting the number of turns to see where it is at. Turn back out to the initial setting and then increase (turn out) by about 1/4 turn then test and continue until desired results, or like someone else mentioned, until you get up to 3 turns out. Then its time to get the next size larger jet.
Also the comments about the exhaust are true, can cause deceleration pop. Also if you have an intake leak, this can cause all kinds of fits.
As MX724 stated above this is a fuel adjustment not air. General rule of thumb. If the Screw is on the engine side of the carb it is a fuel adjustment (turn out richer turn in leaner), If the screw is on the filter side of the carb it is an air adjustment, and Opposite results (turn out, get more air, leaner turn in, less air, richer)
You may try LOWERING the CLIP on the main jet as you may have an overall lean condition (this will raise the jet in relation to the slide) and richen the overall fuel mixture. This would most likely be the casee if you are getting the popping but still have good bottom end response (no hesitation or bog)
If you know someone who can reed a spark plug this would be the best place to start and eliminate some of the guess work. HOPE ALL GOES WELL. GOOD LUCK.
PS. If you already installed a larger main you may run too rich, poor overall response, especially when temps climb you may need to raise the clip on the main jet to lean it out a little / just FYI.
