450 Hard to Start After Mods

I just got my 450 back together after finishing the following modifications: GYT-R Exhaust, DSP Power Now, Cleaned up head, Wiseco 13.5:1 piston, Hot Cams, K&N air filter, vented airbox. I am running 93 pump gas, but I am switching to VP Red for the next time I ride it.

It still has a slight hesitation when you crack the throttle from an idle, and won't start unless bump started when warm. I am pretty sure it is jetting, and I am thinking to go leaner on the needle. Does this sound right, any other suggestions?


its probably jetting.

dont know much about 4 strokes but on 2 strokes when u put on a aftermarket exhaust and muffler u need to do the jetting again.

If you think leaning it out is going to help, why not try the hot start even if it is cold. If that helps, lean is the way to go. I would actually think you need to go the other direction. The mods you have done will need more fuel to create more power. But try the hot start first.

I would think you should go a bit richer.

Try going a step richer on your pilot jet and you may also have to adjust the fuel screw. :thumbsup:

PM'd you......

Your gonna go the wrong way if you lean it out. You need to start by riching up your fuel screw and see what happens with the throttle repsonse. You should be turning out the fuel screw to alow for more fuel. If your at the point where you are at the end of the fuel screw then you need to up your pilot jet. I would also drop your needle clip, one clip and try that. From what I have tried moded four strokes like the fuel. And with that clip one lower it will pull harder in the mid, it also has a small effect on the pilot, which will help you. I found running near the stock main jet was fine. I haven't had alot of testing with it yet on the main. Mostly my riding it mx so your not on the main for more than 2-4 seconds at a time. Your main will only effect you when you hold it out for more than 10-15 seconds.

my two cents

Thanks for the help guys. I should have been more clear. I already richened up the jetting with a 165 main and the JD red needle in the 3rd slot from the top. I am working my way back lean to get it straight again.

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