Ok...This has really got me pi**ed off. I don't know what else to do...i'm ready to light the thing on fire. I have a 2004 Honda 400EX. I have yoshi slip on pipe, uni air filter, and six 1" holes in my air lid box. I re-jet my carb to 152 main, and 42 pilot jets. Replaced my spark plug, valves are adjusted correctly, and fuel screw is out 3 turns. I can't get the thing to start. Yes it has good fuel, and yes the fuel valve is on. What can it possilble be?? Any help would be great...I don't want to take it to the dealer and spend 500 dollars on hourly fees.

 

Have you done anything to it lately? Do you know if there is gas in the carb? Does it smell like gas when you try to start it? Have you replaced the plug lately?

 

As I said in my post, I replaced the spark plug. The only thing new is the re-jetting. I was getting too much back-fire, so I went up in the jet sizes.

 

There are other things that can cause back- fire. Your pilot jet seems a little rich to me. Have tried adjusting that?

 

Too rich?? It started out at 38. Only went to 42. Not enough for it to not start at all...maybe run rough.

 

When you try to start it, is there a strong gas smell? You have the 42 pilot and 3 turns out on your "fuel screw", thats alot of gas. I don't know if that would make it not start though. If it was me, I would take out the 42, put the 38 back in, change the plug, and see if it starts. I know thats alot work. Or you could turn the "fuel screw in to about 2 and change the plug. And I hope this isn't one of those threads that ends with " I had it in the off position" or some other obvious answers.

 

Do you have a stock CDI? Some of the aftermarket ones won't start if the battery isn't 100%.

 

Since you bumped up your pilot, i'd turn the fuel screw in some. All the way in and back out about 2 turns. Your right it should still start .
On my 450 r it didnt like the pilot being bumped up and I went back to stock on the pilot. You might also check to make sure there is no air leak around the clamps on both sides of the carb. Good luck!

 

How does the compression look? Will it bump start?

 

Your main jet seems awful lean for your setup, but that's beside the point.
Many times when I was playing with my jetting the bike wouldn't start up after I had the bottom plug off the fuel bowl to swap jets. I even killed a battery until I tried this- Turn your fuel to "on" and put the bike in gear and then lift the front of the bike up so it stands on the grab bar. When you see fuel start to run out of the carb overflow, set the bike back down and try starting it. Works every time for me.