2002 CRF450r hybrid jetting

[zr440#54]

The fabrication of the project went well, but what should I do with jetting. Only things done to the motor were high comp. piston, and kibblewhites and a curtis sparks exhaust. Right now its at stock jetting. Motor feels hot after 10-15 of riding. Starts on 1st or second 2nd kick telling me the piolet jet is ok. what about mains?
Thanks

[flattrack73]

im gonna be watching this thread. i just got my 02 crf 450 hybrid running also, but with stock jets. its very lean. we have to push/pull start it to get it to run. pretty sure i need valve adjustments but thats besides the point. im looking for a good starting point for the jetting also. also runing a full sparks exhaust with stock internals in the engine.

[ryanowarrior]

im gonna be watching this thread. i just got my 02 crf 450 hybrid running also, but with stock jets. its very lean. we have to push/pull start it to get it to run. pretty sure i need valve adjustments but thats besides the point. im looking for a good starting point for the jetting also. also runing a full sparks exhaust with stock internals in the engine.

If your havin to do that to start it....you may be lookin at a valve job instead of shimmin them!

Piloit size should be couple steps up from factory size

Main jet size should be around 165-170 depending on mods altitude ect..

[9matt2]

If your havin to do that to start it....you may be lookin at a valve job instead of shimmin them!

Piloit size should be couple steps up from factory size

Main jet size should be around 165-170 depending on mods altitude ect..

i run a 172 main, oem needle - 4th clip, 50 pilot with boyesen quickstart, about 2 turns out on screw, i run vp 113 and its a 2003.

[JOHNDOE83]

Jetting a four stroke is easy.

The 50 pilot should be fine as mentioned above.

Tunning the main jet is also very easy, you start large on jet sizes probally a 190ish for a mostly stock 450.

If it doesnt fully rev out and it sputters at wide open throttle, you back down jett sizes in incriments of 5 until it fully revs out to max rpm. Then your main jet will be tuned for max HP at WOT.

Your needle might need to be changed if you have a slight pop or hesitation in the mid rpm range, that means its to lean on the needle and shimming it up is needed.

As long as your bike starts up and doesnt pop on deceleration or backfire then your pilot is fine, if it backfires and pops on decel your pilot is way to lean, sometimes you can compensate for that by turning your af screw out a bit or over oiling your air filter, I suggest just getting a bigger pilot in this case.

All this info is in the FAQs at www.jetsrus.com

Plug color is also kinda pointless unless you actually cut the threads off the plug to read the carbon band at the base of the the porcelain "inside the threads".

The plug color that everyone sees on the actual plug is actually from pilot jet and needle position, it also shows heat range and timing.

[flattrack73]

i know mine needs valves or shimmed, but i want to get the jetting right first and then see how she runs.

[ryanowarrior]

Jetting a four stroke is easy.

The 50 pilot should be fine as mentioned above.

Tunning the main jet is also very easy, you start large on jet sizes probally a 190ish for a mostly stock 450.

If it doesnt fully rev out and it sputters at wide open throttle, you back down jett sizes in incriments of 5 until it fully revs out to max rpm. Then your main jet will be tuned for max HP at WOT.

Your needle might need to be changed if you have a slight pop or hesitation in the mid rpm range, that means its to lean on the needle and shimming it up is needed.

As long as your bike starts up and doesnt pop on deceleration or backfire then your pilot is fine, if it backfires and pops on decel your pilot is way to lean, sometimes you can compensate for that by turning your af screw out a bit or over oiling your air filter, I suggest just getting a bigger pilot in this case.

All this info is in the FAQs at www.jetsrus.com

Plug color is also kinda pointless unless you actually cut the threads off the plug to read the carbon band at the base of the the porcelain "inside the threads".

The plug color that everyone sees on the actual plug is actually from pilot jet and needle position, it also shows heat range and timing.

Great post!!



i know mine needs valves or shimmed, but i want to get the jetting right first and then see how she runs.

I'd get the valves straighten out first then worry bout gettin it runnin good IMO

[Lasher]

thanks that helps with trying to jet my son's 06 crf motor. His motor starts fine, no backfire (god I hate that when behind those 4 strokes) and pretty sure if revs out on top. But when he opens the throttle it will die. I will go and try a richer setting on the needle. You can open it slowly but if you punch the throttle it just dies.

[honda250xrider]

I use a 195 MJ 48 pilot and needle on 4th clip. This is with 12:5 JE piston, ported head, Walsh intake/over sized k&n filter, Hot Cam 2, HMF exhaust.

[JOHNDOE83]

thanks that helps with trying to jet my son's 06 crf motor. His motor starts fine, no backfire (god I hate that when behind those 4 strokes) and pretty sure if revs out on top. But when he opens the throttle it will die. I will go and try a richer setting on the needle. You can open it slowly but if you punch the throttle it just dies.

Sounds to me like the transition from needle to main jet might be to lean, without being there its to hard to diagnose properly.

If thats the case your pilot and needle are fine but when you stab the throttle almost wide open, your mainly on the main jet.

So in my opinion from the info provided, everything is ok except for being slightly lean on the main jet.

I could be wrong, Im not there.