2005 crf450 hard to start when it is hot

I just put new kibble white stainless steel intake valves. When child it will start first kick but when it get hot. It doesn't want to start. Any help what it might be or suggestion. On what it takes to get it to start easier

Assuming the valves are in spec and you are using the hotstart correctly, hard to start when hot normally means its too rich on the pilot circuit. Id try turning the fuel screw in 1/4 to 1/2 a turn.

If the bike ran fine before the new valves, more than likely your valve clearances are slightly tight and when everything warms up your valve clearances are closing up even more. If valve clearance checks out ok I would be looking at the pilot circuit as nzgsr suggested.

I had the same problem but did not really title the thread the best.

Still got lots of help and advice  :thumbsup:


Check thread CRF450 with potential thread. A few down from this one.

I had to do the valves because I burnt up the old intake valves. And it wouldn't start so had to but new valves. I will go through and double check the valve clearance. When I built it everything was on perfect spec. And whenever it is cold. It start first second kick every time.

New valves could easily want the fuel screw adjusted. If it starts easy when cold, it's too rich

I just did the same thing , ive just idled it in the driveway , and took it up the rode a few times , and now it doesn't want to start easy when hot , I have a feeling either i went to fast assembling it and didnt shim real good ,or everything just seated in and it got tight , i can bump start it and it fires right up , i did have to play with the air screw mine needed more gas but i did a different cam at the same time.

I will check the valves to see if they seated ing and the clearance got tighter. And adjust the fuel screw in

This is just an account of what I went through: I just rebuilt my top end, broke it in, readjusted valve clearance, and I had a hell of a time starting it when it got hot. I troubleshot it down to jetting, after rejetting it start 1st or 2nd kick hot or cold. i am running a 48 pilot, 175 main, and the red needle jet (from the jd jet kit) in the 4th position from the top. My air/fuel mixture screw is tuned by ear so couldn't tell you where it's at right now but i started with 2 turns out and turned it in. Also at sea level with moderate humidity (Virginia)

Thanks I will try rejetting

checked mine today one of my intakes was too tight had to go from a 190 to a 180 shim ,guess it just didn't seat right , glad it didnt drop a valve.ive got a left side smashed radiator , so im having to wait a couple days to assemble everything back.for the guy above definatly recheck your clearences , the other 3 shims where still spot on

For what it's worth I run a 40 pilot, 175 main, stock needle 2nd position from the top. 900 ft elevation, 80-95 degrees with 50-70% humidity. 2 turns out on fuel screw. Bike still running a little rich. Will try turning fuel screw in.

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