400ex dies when hot.. suspected electrical problem

[dmolaver15]

My friend has an 02 400 ex and we're trying to figure out why it will run fine, sometimes for a couple hours, sometimes for only a few minutes, and then randomly dies. It will die anywhere from idling to WOT and anywhere in between, and it seems to only do it when it's had enough time to warm up. Once it dies, we can try to start it again and sometimes it will get going again, other times it doesnt want to start up right away, but will fire right up like nothing ever happened if you just let it sit for a few minutes. The quad runs awesome in between its stalling fits, no sputtering or anything, which makes me think it's not really a fuel issue at all. The lines are all clear, and also the air filter and intake are all clear. The machine has fresh oil and a new filter also. So far we've done a complete overhaul of the carb and that hasen't done anything, and we've swapped out the CDI box with a friends off of his working 02 400ex.

We have yet to check the spark plug itself, (dumbf*** lost his tool kit and nobody has that damn socket in stock) but the boot, wire, and ignition coil all appear to be okay. Other than looking into the spark plug... what else should we be investigating?

[CJM]

Ground wire? Check all electrical connections and fill with dielectric grease

I had a similar issue where the bike would shut down whenever I went in so much as a puddle. I checked and made sure all electrical connections were good and filled them with dielectric grease including the spark plug boot and I checked all the grounds..no issues after that.

[honda400ex2003]

coil possibly? it would be worth testing anyway. steve

[dmolaver15]

Originally posted by honda400ex2003
coil possibly? it would be worth testing anyway. steve

tested the coil with a timing light, coil is good and i would assume that proves that there aren't any bad grounds. Just in case though, where is it grounded? shop we brought it to to test the ignition said the pilot jet could be clogged, so we pulled it and cleaned it out and poked some wire through it, still has the same problem.

I'm assuming that using the test light has ruled out any electrical problems, so i'm thinking it may actually be a fuel issue after all. SO.. what now?

[honda400ex2003]

i believe the coil itself is grounded where it mounts to the frame.

stator would be out really since it keeps everything working when it shuts down. ive seen spark plug wires that will develope problems also but just doesnt seem to fit the bill for this case. im still thinking about this... steve

[honda400ex2003]

coils can also work fine until they get warmed up. I had a boat do this once. it would start not getting enough spark to stay running fully but it was a twin so it would say running. just another possible thing to try to change fully instead of just testing. it is easy at least to change. steve

[smorris1]

cdi maybe? The cdi would make my 250x die all the time when I was riding it.

[togup]

Inspect your kill switch circuit , grounding this circuit stops the engine ,possible pinched or naked wire? Would explain randomness of your problem.