06 CRF 450r MRD exhaust Jetting Question!


I just bought a low to mid spec exhaust from MRD to replace the stocker, I also got the quiet core and Spark Arrestor.

I am currently running a 172 main 42 pilot and JD red needle in the 6th slot from the top. with no other mods to the bike.

After the install of the exhaust the bike starts pretty well, But the low to midrange just doesn't have the snap it did with the stocker it rolls on fine but with quick throttle twist it just doesn't respond like it did with the stock exhaust or have the power the stock pipe did. It has some spots where it burps about 1/2-3/4 throttle while holding steady. I feel like the top end pulls like the stock pipe. I am confused since the bike feels rich on the bottom, sluggish and slow to respond but, you would guess lean do to the new pipe? Maybe with the quiet core and spark arrestor it is flowing less than the stocker?

I pulled the plug today and it looked slightly lean. I just pulled the carb to find it was very dirty! Not good!. So I tore it down and cleaned everything out.


Thanks in advance!

Hey man, my uncle had the same problem with his stock 2003 450. He was told by his friend to put a 45 piolet jet into it. It made a huge difference. We were at Washugal at the time. Going up HP hill, he pulled wheelies all the way up. So give that a try. The jets cost about 5 bucks.

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