Hi all,

I have a 2004 Honda TRX 400EX that refuses to start.

Everything seems fine - spark, fuel supply, carb.

I don't have a compression tester but it has run before very recently no problem. It sat for a few days and now it just won't start.

I have even taken the carb off and sprayed carb cleaner directly into the intake and still nothing. Pulled the plug and sprayed gas into the hole - still nothing at all.

Engine turns over fine with the electric starter. Spark seems fine when out of the engine.

Tried replacing the plug, no difference.

I am stumped. Even my mechanic friends can't figure it out.

I have read many forums for ideas and can't find anything helpful. Some people suggest checking valve clearances and timing but I think that it would at least react somewhat to my attempts to get it to go. It just does not combust whatsoever.

Any help or advice is greatly appreciated!! Thanks in advance!

 

A rough compression check can be done by removing the plug and putting your thumb over the plug hole, press down and spin the engine on the starter. If it has enough compression to blow air past your thumb, it has enough to run. If that is OK, timing, either ignition or valve may have slipped check the flywheel TDC mark agrees with TDC by the piston, then check the TDC mark agrees with the one on the cam sprocket at TDC on the compression stroke.

 

It was the valve clearances finally.

Problem solved.

3 of the 4 had no clearance at all.

Adjusted the 2 intake valves to .004" and the 2 exhaust valves to .005" and she started right up after.

Thanks!

 

I same problem but my vales are adjusted right and everything and it still acts like the vales are still to tight. Ow if we set them at 0.07 it runs dont know what to do

 

Never worked on an EX but what is clearance supposed to be? Am assuming by 0.07 you are referring to mm so 0.003" which doesn't seem excessive to me.