Jump to content
Sign in to follow this  

motor running a little choppy

Recommended Posts

I just finished completely rebuilding my top end and it seems to run fine but there's a decent amount of backfire on decel and it runs choppy just cruising with about half throttle, I'm thinking I need to rejet my carb but any other suggestions or opinions would be much appreciated, thanks  

Share this post


Link to post
Share on other sites

after doing mine I took it out to do some rejetting out on the track and it developed quite a lot of back firing,turns out I hadn't done up the exhaust header bolts when putting the top end back on,might pay to check all the easy stuff first and rule out any exhaust leaks

  • Like 2

Share this post


Link to post
Share on other sites

well I noticed I didn't have a crush washer on my header, but I put some hi temp silicone on it for a temporary fix, but it runs rough a little under half throttle which I guess would be cruising speed or constant rpm, so would that be the pilot or the main jet, and should I be going up or down, i've never re jetted before 

Share this post


Link to post
Share on other sites

I had run my bike with no crush washer for 100hrs,it won't leak from there unless something is warped,I put one on when I realised that it was supposed to have one though.What jetting specs do you have now? standard? pilot jet is idle and to 1/4 throttle and main jet is 1/4 to full throttle,knowing whether to go up or down on pilot depends on how far out the fuel screw is turned out,if you have to turn it out anymore than 3 turns you need a bigger pilot jet,mine has the 45 still in it which is standard so you shouldn't really need to replace just a bit of fine tuning with the fuel screw,it's something you are just going to have to play with to get it right.

 

Don't bother doing any of this if you still have standard jetting,if you do then get a JD jetting kit and uncork your exhaust or get an aftermarket exhaust,the kit will give you the proper needle and clip position and recomend the right main jet to suit the mods you have or don't have,pull your plug out and check the colour to give an indication of rich or lean. 

Share this post


Link to post
Share on other sites

I haven't taken the carb apart yet but I think It might have a jd kit already in it or at least that's what the guy I bought it from told me, but I did a completely new top end and had my head gone over and it has new everything now, and the whole top end is an 07 kx450, I could have just a bad spark plug too, not sure

Share this post


Link to post
Share on other sites

Chuck a new plug in as it's cheap and easy,for peace of mind undo the float bowl and pull out the main jet and see what it is so you can be satisfied as to what it is,pulling the needle out from the top of carb is easy as with the tank and seat off so you can check needle type and clip position

Share this post


Link to post
Share on other sites

well I took my carb apart and I have a 180 main 48 pilot and the clip on the needle is on the forth one down 

Share this post


Link to post
Share on other sites

023.JPG

I also took my plug out and it looks like it might be running lean but I'm not sure 

Share this post


Link to post
Share on other sites

Oh and the fuel screw was a little over 1 1/4 turn out  I think 

Share this post


Link to post
Share on other sites

a white tip means running lean and tan brown means spot on,black is rich,bit hard to tell in the photo though.The jetting sounds like it's right for your set up,maybe some of the jets are blocked,I just re did my jetting and I have full KX exhaust,KX airbox,delwest KX valves(bigger than KLX) and I run a 170 main jet with red needle originally on 4th clip down but plug was a bit white so I put it down one clip to raise the needle and the fuel screw is 2 1/4 turns out,im just about on the limit for changing to the 48 pilot,I have the 45 stock in,my plug is a perfect tan brown so ill leave as is and if I need to go any more turns out I will need to go to a 48,your setup was probably similar where the screw would have been right on 3 turns out to get it running so changing to a 48 means it should be very close to being one turn out which it is for you,

  • Like 1

Share this post


Link to post
Share on other sites

I'm not sure which type my needle is but i'll try moving the clip down one and see if that helps

Share this post


Link to post
Share on other sites

If it's tan then you are good,I would swap the main and pilot jets for new ones of the same size to rule out blocked jets being your problem,if you have carby out then a good clean and new seals etc will give you peace of mind and then you can start looking in other areas if the problem persists.

Share this post


Link to post
Share on other sites

I cleaned the carb and jets thoroughly and moved the clip on the needle down one, which seemed to help the idle and popping a bit but still sputters at higher rpm, also is the ncv r needle stock?

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×
×
  • Create New...