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XR250R jetting please help

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Hello, I have a 2002 xr250r and I just did a carb rebuild kit and it seems to be popping in the high rpm range really bad, it seems to run fine in the low and mid rpm ranges. The needle is set in the 3rd slot of 5, the main jet is a 132, the pilot jet is 48, and the fuel screw is 2 turns out. The air box has additional holes drilled in it and the exhaust header welds where ground down. What would you recommend I do?

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Did it do this before the rebuild kit?

What's your elevation?

Did the kit replace the jets with new? If so, are the jets genuine Kiehin or knock off jets? A 132 knock off jet is not necessarily the same orifice size as the genuine Keihin.

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High RPM or WOT?  They are not the same.  Jetting is a science, but its an easy one if you know your terms and definitions.

Also, as stated above, only use genuine Keihin jets.  Everything else is garbage.

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Popping or backfiring is a lean condition. Sputtering that clears up is rich. Sounds like you are running lean on top, or have an air leak. Recheck the carb install for boot issues where it could draw additional air. If you lower the needle clip that will richen the mixture, but somewhere near wide open the needle is out of the picture and the main jet size needs increased.

Basic jetting, for me, in general is at sea level use stock jet sizes, needle clip second from top and air screw 1.5 turns out. Main jet lower 4% for every 2500 feet above sea level, pilot jet drop one size for every 5000 feet of elevation. Example, I am at 5600 feet, my main jet is 92% of stock size and pilot jet one size smaller.

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Did it do this before the rebuild kit?
What's your elevation?
Did the kit replace the jets with new? If so, are the jets genuine Kiehin or knock off jets? A 132 knock off jet is not necessarily the same orifice size as the genuine Keihin.

I'm at 1,300 feet I have replaced the old jets with jets from sigma racing I also changed the main jet to a 145 and it is still doing it, I also found out the fuel valve was not giving good flow. And it does it at high rpms but gets much worse at WOT

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hi i will explain jetting later for now check your boot from the carb going to engine,start bike set high idle,get a can of wd 40 and spray the boot if the rpms drop theres a leak(checking vaccum leak),also check where muffler is joined/attached to exhaust for leaks,mine had the leak there,was popping and throwing flames even r1 and cbr's couldnt beat hahaahaha.so you are first checking vaccum air intake leak or exhaust leak,secondly check the tiny rubber o ring that goes in the air screw(oring then spring then airscrew),probably you forgot to install tiny oring,or vaccum leak.another method since its poppin at wot or high rpm,rev in neutral high rpm,hold at a constant rev and pull choke slowly if the rpms increase its lean,if it drops its getting rich/too rich and okay!check and do what i said,if not then i will advise what to do.then its basically playing with the needle clip position.

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On 10/21/2018 at 6:50 PM, kdxyardsale said:

Popping or backfiring is a lean condition. Sputtering that clears up is rich. Sounds like you are running lean on top, or have an air leak. Recheck the carb install for boot issues where it could draw additional air. If you lower the needle clip that will richen the mixture, but somewhere near wide open the needle is out of the picture and the main jet size needs increased.

Basic jetting, for me, in general is at sea level use stock jet sizes, needle clip second from top and air screw 1.5 turns out. Main jet lower 4% for every 2500 feet above sea level, pilot jet drop one size for every 5000 feet of elevation. Example, I am at 5600 feet, my main jet is 92% of stock size and pilot jet one size smaller.

good advice right there!and also check tiny rubber oring in the airscrew and vaccum leaks!and then jetting!i always start with the vaccum leaks first before carb,experience hehe!

 

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