High altitude jetting

[01warriorutah]

Hello all, new guy here. I just picked up an 01 with an FMF pipe, UNI foam filter and stock air box. It is running OK but I raced a guy with a bone stock 97 and he walked all over me. I did noticed a slight stumble off idle so I pulled the carb to clean/adjust it. I found a 130 main jet. If stock is 145 why did the first owner drop down is size? I ride any where from 4200 to 8000 ft in alt. Any ideas about what size main I should start with.

 

[yamarider]

My guess is that the 130 is a dynojet. Dynojet uses a different sizing scale than mikuni jets, which confuses the **** out of everybody.

I'm not sure exactly how much altitude effects jetting, but i'd start with a 147.5 mikuni jet and see what it does.

The stumble off idle could be either the pilot jet/fuel screw, or the accelerator pump not working properly.

 

[01warriorutah]

Ok thanks. Ill check out those two things and report later.

 

[01warriorutah]

Well I have tried piolet jets 1 step higher and 1 step lower and messed with the piolet screw. I found that with the lower jet(40) it wouldn't run without throtle input. And it smelt really bad. The higher (45) would run but it died if I gave it gas. The kicker is both jets still have a bad off idle stumble. ??? ??? ???