uncorking troubles

I uncorked my scooter today using a 175 main jet. Now it works great up to about 4000 rpm under load then it falls on its face as though it is running out of fuel. Any ideas? Your help will be greatly appreciated.

Have you unplugged the airbox by ditching the snorkle and block off plate? Did you carve out or replace the intake manafold? Are you still running the stock exhaust tip with out hole sawing it or replacing it with the HRC piece?

If you have not done the above the bike will fall on its face because there is no flow. It now has gas, now it needs AIR.

Go to www.XR650R.net and click on "Making the XR650R Run Right! (Uncorking It)" for the full details with pics and part numbers.

All right! I found my problem. The plastic insert just forward of the rubber boot was causing my difficulties. I missed removing it.

Thanks for the help.

I found another article that you might be interested that was posted on Honda XR.com Check out the Air Box Modification article at www.HondaXR.com/tips/airbox .

It was posted by Qadsan who posts here too, and from what I have read is one of the more knowlageable folks on here.


If you have properly Un-Corked your Honda, it will run great. HOWEVER, if you make the investment in a high quality aftermarket COMPLETE exhaust system, which will include headers and silencer, ditching the entire stock exhaust system, then you will then experience TRUE power. The bike will NOT fade out in the upper mid-range. The bike will be intrusively LOUD, but will produce the quality power it was intended to. Touchiness off the bottom end will be softened a bit. Mid-range will be broadened and strengthened enormously, blending seemlessly into a good, truly strong, Top-end output. From experience with my 650R, I would highly suggest an aftermarket "race series" complete exhaust system. Jet the bike 3rd clip position, and 175 main.

I disagree with the comment about the full race exhaust system. The XR650R pipe shootout that was done a while ago shows there's very little to be gained over the stock HRC setup and in many cases the big name aftermarket pipes didn't perfom as well as the HRC setup at low to mid throttle. Honda has some sharp folks working for them and the stock header is about the best you can buy for low to mid throttle performance. A larger header typically sacrafices power down low in exhange for gains in the higher RPM. In order to get the low to mid range power back after installing a larger header, you need to install a different cam and high compression piston. The torque start dropping off at 5,500 RPM and the horsepower starts dropping off the XR650R by 6,500 RPM, so unless you plan to Motard your bike or run mostly at WOT, the stock header is probably the best choice for most off roaders. Aftermarket pipes sure look nice and they usually save weight, but they aren't always the best choice for everyone.

I'm one of those guys who blew a wad on a full exhaust system. Got the Big Gun which after wasting 4 hours installing it, I refer to it as the Big Pain in the Arsch! :) I tapped on that thing for 2+ hours with a rubber hammer to get it to line up correctly and will probably need a saws-all to get it off. :D And when I ride it down the highway, Harley Riders pull over because its so loud. :D The coin could have been better blown elsewhere. Anyway, I recall a bunch of guys from previous posts liking the WhiteBros E-series muffler pretty well. And if your right calf is getting hot then there are some places that can ceramic coat your stocker header and minimize the heat trasfer.

What! :D Qadsan posting stuff on another forum! Why that two-timing poster! :D My God! What's TTalk coming too??!!! :D

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