I have a 2000 400ex with a K&N Jet kit, no airbox lid, and a big gun complete exhaust. I'm running a 170 main. This thing is VERY hard to start, it backfires like crazy until it is warm. What's up?

 

My 400ex does the same thing .. it isnt too hard to start but it does backfire alot. I am having my edelbrock qwiksilver carb put on right now and they say that is supposed to help it start alot easier in cold conditions. i'll let you know how it is when i get it back.

 

Try changing the pilot jet in carb to a #42 or #45--stock is a #38. This will help it alot on startup. If you need help in locating pilot jet; just ask.

 

When I installed the K&N Power Kit, I replace the Pilot jet, it has always been hard to start. My thinking is that the f/a mixture screw is out too far. Any idea how far out it should be? 1-1.5 turns?

 

I have mine 2.25 (2 1/4) turns out. It starts MUCH easier than it did when it was stock even in the cold, after setting for a week. Choke it and it starts. Dies occassionally, but it fires almost immediately. When it was stock, that thing was cold blooded big time.

Not related to the hard starting, but once warm have you checked your plug at 3/4 to full throttle?
170 main seems kinda big, even without the airbox lid. ?? Just curious.

 

Why are you running a 170 on your bike? That is kinda big.. I have my motor built and i run a 170.. Try dropping it to a 165 or so.. if not lower. Or do what ever u see fit..

 

<< When I installed the K&amp;N Power Kit, I replace the Pilot jet, it has always been hard to start. My thinking is that the f/a mixture screw is out too far. Any idea how far out it should be? 1-1.5 turns? >>

What #pilot did you put in? I dont know if K&amp;N jets are sized as Kehin. If they are a 170 has GOT to be too rich. Do you still have the stock cdi(ignition-black box) The White Bros cdi make it hard to start cold. If jetted properly it should start right up. The XR400 bike has the same engine as the 400ex but has much richer jets--I think pilot is a #50. I have never played with fuel/air mixture but it may need adjusting also.

 

Where is the pilot jet?

 

check your plug

 

Switch to the splitfire spark plug. That helped my starting. Next step is the Edelbrock Carb. Ultra150 is right everything that I have read said this carb eliminates hard starting. Also no rejetting just a screw adjustment.