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Queries to XR250R Mods (uncorking)

Posted: Sat Oct 22, 2016 8:31 am
by 1303
Hi, Everyone, new to this site and off roading in general, let me tell you a bit of background, I am the proud owner of a very nice 03 250 xr and due to my age (and ability) I restrict my off roading adventures to gentle green lanes and the odd not so green ones. My question is now I've uncorked my exhaust and removed the snorkel i get a bit of back firing and popping when i shut the throttle off, is this anything I should concern myself with? I have read several topics on the matter and they talk about rejetting the carb and making adjustments but they are all well beyond my capabilities, would it be ok to carry on riding (about two hours at a time) or do i need to have my carb looked at.
Your replies will be very much appreciated.

Re: Queries to XR Mods

Posted: Sat Oct 22, 2016 4:47 pm
by JoeRC51
You need your carb rejetted. You increased airflow thru the motor , now it needs more fuel to go with it. Running lean makes the motor run hot.

Re: Queries to XR250R Mods

Posted: Thu Oct 27, 2016 10:39 am
by 4Strokes
I agree with Joe. You've increased airflow through the motor so now you need to increase fuel. You didn't mention whether you replaced the stock air filter with an aftermarket high flow filter (Uni, Twin Air, etc) but depending on the elevation where you ride, you'll probably need to bump up the main jet to 135, slow jet to 45 if not already, and back out the pilot screw 1-3/4 to 2 turns. Rick Ramsey's personal website has some info on "uncorking" the '98-'04 XR250R.

Re: Queries to XR250R Mods (uncorking)

Posted: Sat Oct 29, 2016 2:56 pm
by 1303
Would it make any difference if i were to go down the vw tail pipe route? I have purchased a vw pipe but I cannot get it more than half way down my tail pipe there appears to be a very small step in the exhaust that prevents the tail pipe sliding down. Would i still need to swapthe jetting if i use the vw tail pipe

Re: Queries to XR250R Mods (uncorking)

Posted: Tue Nov 01, 2016 5:32 am
by Plud
1303 wrote:Would it make any difference if i were to go down the vw tail pipe route? I have purchased a vw pipe but I cannot get it more than half way down my tail pipe there appears to be a very small step in the exhaust that prevents the tail pipe sliding down. Would i still need to swapthe jetting if i use the vw tail pipe
Yes, you even if you put a stock pipe on it you've modified the intake which in many case will have more effect. Also motorcycles have been jetted lean from the factory for decades.

Re: Queries to XR250R Mods (uncorking)

Posted: Tue Nov 01, 2016 10:50 am
by 1303
Can you advise me on where to purchase the jets from? I guess it would to be an official Honda dealer and do they carry all sizes of jets and would they be able to confirm the size of jets I require. Are the 135 and 45 jets they will always have in stock.
O bye the way I have now sorted the insert it is now fitted to my bike sounds good (not to loud) but need to get the jets fitted before I venture to far. (Would post pictures but don't know how)

Re: Queries to XR250R Mods (uncorking)

Posted: Tue Nov 01, 2016 5:20 pm
by Plud
Dealers should have various sizes of jets, you need to know what carb brand and often the jets come in short and long versions as well. Jet sizes depend on a lot of factors, mods, elevation, etc. You're best bet is to learn about jetting, how to determine if you're lean or rich and start with the factory jetting and work from there.

Here's a good start: viewtopic.php?t=5

Unless you get lucky you may become really good at removing and installing your carb, just be glad it's not on a 4 cylinder sport bike.. those can be a serious pain in the rear.

Re: Queries to XR250R Mods (uncorking)

Posted: Tue Nov 01, 2016 7:39 pm
by JoeRC51
If it runs better with the choke on , it's lean. If it runs better with the sidecover off of the airbox , it's rich. Make only one adjustment at a time so you can see your results or you could be at it way longer than necessary.

Re: Queries to XR250R Mods (uncorking)

Posted: Tue Nov 01, 2016 7:41 pm
by JoeRC51
JetsRUs.com will tell what series jets you need by bike model.