honda xr650r backfiring, help needed !!!!!!
 

hi all , i have a problem that is taxing my fixing skills, well here goes, i have a honda xr650r i got it after it had sat in a shed for 5 years doing very little, it has 1000k,s from new and it,s a 2000 model, when i got it i put new fuel in gave it a oil change and filter checked it over, then gave it a run, my problem is that when warm if i open the throttle and hold itat 1/2 throttle it backfires through the exhaust and pops and bangs , here is a list of things i have checked.
1, new spark plug N.G.K iridium
2,carb taken apart cleaned , jets checked 175 main , 65 pilot, air screw 1 3/4 out, needle 2nd notch from bottom
3,cylinderhead to carb rubber checked
4,decompressor checked and adjusted
5,valve,s checked exhaust 0.20 inlet 0.15
6, all electrical connections checked , all clean
7, coil lead checked, and plug cap ,all good
8,running unleaded supreme
9,air filter clean and in good condition
10, exhaust standard but with unrestricted baffle
the symtons all point to a air leak, and running lean but i can,t seem to find a cause, well chaps theres something to get your teeth into, any thoughts kindly appreciated, thanks alot freddy

You've got an unrestricted exhaust but standard jetting... You bike is probably running a little lean (backfiring is burning air)...

My XR used to pop and bang with my unbaffled pipe too.

How is the power ?? Pulling smootly and cleanly ??

hi ted
 

hi there mate, thanks for taking the time to reply, my bike was popping and banging with the standard pipe insert in, i know the history of the bike and it was as it was as it came from the factory, anyway this afternoon i decided to take your advice and mess around with the jetting, i have gone up one size on the main , this made a considerable difference, so tomorrow i am going to order some jets and a larger slow running jet , and take it from there, i just find it hard to believe a bike could come that lean from the factory, well once again ted thanks for the nudge on what to look for, good work, cheers freddy

Is yours a UK or US bike ?? There is a MAJOR differnce in them... Sounds like Uk from the jet specs though..

I upped my main jet to one bigger.. It solved the popping but it also make it very "boggy" on acceleration..

Mine was a BITCH to start until I upped the pilot jet (slow running jet) and it made a considerable difference in a good way...

If you find that your new bigger main jet is too "boggy", put the original back in but raise the clip a notch and try that.

Most MX bikes come lean from the factory to get through emmisions laws so dont be surprised. If your bike starts ok from cold, then i dont recommend messing with the pilot jet... Do you need choke ???? how many kicks from cold ??


If you search my old threads from about 2005, 2006 (when I had my XR650's), I posted all about my jetting and the sizes I used.....

Best regards, ted

hi ted
 

hi there ted, yeah my xr is a uk spec bike, i have got a 178 main and a 180, i have also got a 68 pilot that i am going to exsperiment with, althought in saying that i put the 178 in and the bike came to life , what i was after all along , it is no problem to start from cold or if it,s hot, i still find it hard to believe that they would let a bike out the show room running like that, as i know for sure that it has not been touched since it had its p.d.i !! i will look back at your thread s and see if i can,t gleam some more useful info , thanks again for taking the time to reply, freddy