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Xr400r jetting

Posted: Thu Mar 02, 2017 9:59 am
by James 00
Hey I have an 2000 xr400r and I have done all the Gordon's mods to my bike but the jetting is way way to rich. I live western Washington and run from 500 to 3500ft... everything is stock except the Gordon's mods..air filter is an Uni. Needle in the 3Rd grove also. Ive tried going up on jets sizes on both jets Wich made it way to rich the plug was BLACK. I went up 1 size on the slow jet(from stock) I had a hard time starting and running without popping. The fuel screw I could close all the way and the bike would not die!!! So back to stock jets. At stock the screw is out 2 turns and starts fine...... any ideas on why my bike won't except the jetting changes like all the other bikes I read about. They run higher altitudes and higher jets sizes with stock like me?

Re: Xr400r jetting

Posted: Thu Mar 02, 2017 1:08 pm
by 4Strokes
Hello and welcome. If the jetting is way too rich and the spark plug is black, you would want to reduce jet sizes, not increase. First of all, what is the bike doing that is a problem?

Re: Xr400r jetting

Posted: Fri Mar 03, 2017 10:10 am
by James 00
I did the Gordon's mods to it to get a little more grunt down low... it runs fine with stock jets in it now but curious why my jets stayed same and everyone else's when way up in size and my altitude is lower then most

Re: Xr400r jetting

Posted: Sat Mar 04, 2017 2:37 pm
by 4Strokes
It's hard to tell why without knowing exactly what was done with the uncorking. I know the XR came slightly rich from the factory so that might have something to do with it. Did you leave in the stock restrictive air filter?

Re: Xr400r jetting

Posted: Mon Mar 06, 2017 2:45 pm
by James 00
I put an uni filter in ground down the welds on the header pipes opened up air box and drilled holes in the stock spark arrestor.

Re: Xr400r jetting

Posted: Wed Mar 08, 2017 12:46 pm
by 4Strokes
If the bike seems to be running fine throughout the throttle range chances are it's close enough for your elevation. One last step I would do, would be a spark plug reading: How to Read a Spark Plug

Re: Xr400r jetting

Posted: Mon Dec 25, 2017 1:18 pm
by JMerrell46
Hopefully you got your bike jetted and figured out by now. But in case you haven’t, I just had he same problem with my 99 XR400. Plug was black (indicating too rich), but all other indicators were saying too lean (backfiring/popping, hard to start, rough idle, better on choke, Gordon’s mods complete). Put a 160 and 60 in, runs like a CHAMP!! Forget the plug, listen to the other indicators and richen up your jetting. Happy Trails!