uncorking question

6 replies to this topic
  • kd4pxv

Posted September 23, 2003 - 04:39 PM


I uncorked the brp a few weeks back. the power is
great and it runs a lot cooler. I drilled out the
pipe with a hole saw opened up the airbox changed
the intake gromet used the stock needle on the 4t
clip and used a 172 main jet 68 slow jet. I get a
miss or a backfire when i hit a jump hard. it seems
to be rich.the plug is somewhat black.i ran the air
screw all the way in and it did not cutoff. what do
i need to do. i am at about 1000ft elv. here in
western n.c. help please 02 xr650r

  • JR650

Posted September 23, 2003 - 08:06 PM


The jets sound about right to me, im at about 1200ft and im running the 68 slow/170 main. Try cutting the baffle off the end of the tip, that secondary baffle that is held by the four metal straps off the end of the spark arrestor, it will get a bit louder, but will breathe better and will lean out the mix some, i also noticed a little more low end snap. I cant say ive ever had it hesitate on me while jumping. This "miss" is it a loud pop? like really loud? or just a hesitation? try chopping that baffle and see what happens, you could always tack it back on, but honestly, it doesnt get enough louder that you will probably care. Good luck, JR

  • Old_Man_Time

Posted September 23, 2003 - 08:52 PM


You may not of needed the 68 slow jet. I didn't need the 68 slow jet until I installed a mild cam. The 65 did fine and I had the exact setup you have. They also make a 70 slow jet. You might buy it also and experiment. I think the 65 slow should do it. If after installing the stock slow jet it pops after you rev it then put the 70 slow jet in. As far as your main jet goes anything from 170 to 175 should work fine at your altitude. You might try the power up needle and seat? After all it was designed for the power up kit.

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  • kd4pxv

Posted September 24, 2003 - 06:35 PM


thanks for the advice.every time it has did it i
had been hard on the throttle on a jump or a hill.
about 10 seconds after when i crack the throttle
again it pops or backfires and cuts off. thats
the only time it has did it. i think i will go
back to the 68 slow jet and try it

  • ill_caper

Posted September 24, 2003 - 07:26 PM


To be honest. The best thing I ever bought for my Xr was the edelbrock carb. I know it is expensive at 400 but it was well worth it. After the edelbrock it started first or second kick cold,warm,even if it fell over. Also the throttle response was incredible. My $.02. Take care, D :)

  • qadsan

Posted September 24, 2003 - 07:35 PM


...every time it has did it i had been hard on the throttle on a jump or a hill...

This is sounding more like a float/fuel issue to me. You may want to try lowering the float a mm at a time to see if that helps after you've tried all the other suggestions.

I used to get similar symptoms on jumps, but especially when climbing a large steep rocky or rutted hill where the bike is bouncing around all over the place. I played around with the float levels a bit and improved things, but grew frustrated with other carb issues such as trying to quickly start the bike after a fall, rejetting to get the most from it for the different locations I was riding (sea level to 7,000 ft) and I wasn't satisfied with the throttle response. The Edelbrock carb (click my signature for details) solved all my carb issues. It has an internal fuel cell that prevents the fuel from sloshing around (unlike the stock carb) and the bike will literally run on its side. Also, fuel doesn't spill out the vent tubes and it starts first kick after a fall unlike the stock carb. It also has a patented dual vent design so that it maintains the same air/fuel ratio from 0 to 10,000 feet and I no longer have to fiddle with jetting when I ride at different locations to get the most from my bike. The accelerator pump also significantly improves the off idle throttle response if you whack open the throttle from down low. Honda should have at least given the XR650R a pumper carb like they did for the CRF450 and all modern race bikes (Yamaha, Suzuki, Kawi, KTM, etc) now feature pumper carbs just like the muscle cars of the 60's & 70's went to when they needed improved off idle performance. I hope you nail down your issue with an adjustment or by fine tuning your jetting, but there's several people here who have gone to aftermarket carbs with great results if you get frustrated with the limitations of the stock carb for your riding applications.

  • kd4pxv

Posted September 25, 2003 - 05:52 PM


thanks for the reply. i will adjust the float and try
the 65slow jet. i like the idea the pumper carb. that
will be later on. this is a new project for me. i have
not rode much in years.i miss my old 84 xr500 it was a
blast.sold it about 6 years ago.

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