No Fast Idle On Cold Start

[pk400ex]

When starting cold has no fast ilde with choke on, starts up but will not stay running, won't idle until warmed up. Checked for vacuum leaks,none found,tested air cutoff valve seems to be ok, cleaned out idle/pilot circuit,set pilot screw,checked valve timing, adjusted valves. It also burpes threw carb when cold,once it warms up it runs good. Any help would be very cool on how to fix it.

2002 400ex
hmf slip on
kn air filter
165 main jet
stock pilot jet 38

[400eXr1d3rZ]

Drop your main to a 155, put a 42 pilot in and it'll start up perfectly and idle good, also mess with your air/fuel screw 2.5 spins out.

BTW Are you using keihin jets?

[pk400ex]

Thanks for the help, the jets are keihin,I will go with the 42pilot jet, why change the main jet? It runs awesome after it warms up. I had this problem before when the quad was completely stock,when I bought the slipon ( hmf sport series ) it came with the 165 main jet so I put it in. What does the main jet have to do with the idle? I was told the main jet controls 1/2 throttle to full throttle operation and that the pilot jet controls the idle to 1/2 throttle operation. Was I miss informed?

[400eXr1d3rZ]

Because 165 is too rich, yes I main is 1/2 to full. I wouldn't stay rich, because of carbon build-up, put a 155 in and you will notice the difference in how the throttle reacts.

[BigMike]

I had the same problem. Just this week, I swapped my pilot from a 38 to a 42 and the problem vanished. Pump throttle twice, tap the starter and it fires up and idles perfectly. No choke needed.

Mike