Help Diagnois Problem

[SMTRDSPORT]

2005 Honda 400 EX.. Engine mods are pretty much stock... slip on pipe, filer, jetted... The bike has ran perfect for years and all of a sudden it won't run continuously without dying.

The Problem:
The bike starts fine... start to ride it for about 15-30 minutes and it'll die as if it lacks fuel, spark, etc.... so you'll wait for approximately 5-10 minutes and it'll start back up and run perfect for another 30 minutes perhaps longer/shorter and it'll die again...

What I've done to fix it, yet still unsuccessful:
I rode it one day until the delayed problem occurred thinking it wasn't getting spark.. once the bike died I pulled out a spark plug and attempted to start the bike with the spark plug next to a bolt... it showed spark.. so I new I had spark, must be a fuel issue. I removed the carb, checked the bowl on the bottom of the carb thinking maybe theres water in it, etc.. nothing.. blew out the jet and I did get a piece of something/grit come out... figured there was my problem... through everything back together, also added a inline fuel filter between the gas tank and the inlet to the carb... Assuming I figured out the problem and the bike was back to normal I went for a ride... made it about 2 miles down the road and the bike dies on me again.... I wait a few minutes and it started back up and ran for a while eventually dying...

I'm lost now, dunno if its electrical? anyone else had this similar issue with there 400EX periodically dying? Any thoughts? I dunno if its a CDI box problem, etc..

Any help would be most helpful..

[rideracelivemx7]

well i belive once a cdi dies it dies and doesnt come back on after 5 minutes. you siad its been good for years. a 2 stroke is solid for a year. a 4 stroke is solid for a good couple years. but things wear and tear in the long run. check compression. check your valve gaps. mabe its time for new valve springs. i just happened to check mine in time and they were junk. mabe just time for new rings. but id check for compression. should be around 100. anything less its deff time for a new topend. let me know how it goes

[CSR400EX]

also check your gas cap, it may be causing the tank to vapor lock and act like your out of gas. next time it does that, loosen your gas cap up a bit and see if it will start. if so, your cap needs replaced

[Eviltanker]

I agree with CSR400EX Start small work up. I had the same thing happen to me, all it was is the vent on my gascap was bad. put a new on in and I was fine again.

[NickG5755]

when it dies listen for a like woosh of air going into the tank when you take the cap off..

[QuadManiac]

Once had the same problem, after a lot of troubleshooting found that a spider had crawled into the gas cap breather tube and died, plugging it up. Fuel flowed into bowl slowly, ride for 30 minutes, as fuel in tank dropped the plugged breather tube caused a vaccuum in the tank which prevented fuel from filling the bowl fast enough. Let it sit for a few, and the tank would slowly fill with air again, releasing the vaccuum, to start the cycle all over again.

[SMTRDSPORT]

I'll try the gas cap idea tonight... I do have a stubby breather type hose on the cap... I've talked to local dealer as well and they've also suggested maybe the (forget the name of it now... the piece inside the gas cap) is bad... I'm thinking its a fuel issue as well at this point... almost like somethings in the tank swishing around causing a glog, then once the bike dies, whatever it is floats to the bottom and allows for the bike to start..

Thanks for the suggestions so far guys/gals... I'll try the gas cap idea and report back... I know the top end of the motor is fine... the bike runs very strong, no ticking, etc.. when its running.

[powermadd400ex]

Originally posted by CSR400EX
also check your gas cap, it may be causing the tank to vapor lock and act like your out of gas. next time it does that, loosen your gas cap up a bit and see if it will start. if so, your cap needs replaced
i have to agree with him as well, the same thing happpend to my friends z400

[SMTRDSPORT]

you guys are geniuses... went for a short 2 hour ride this evening using the gas cap off my other 400EX and the quad didn't die once... Gonna have to get rid of the stubby breather and try a regular hose now before I run out and buy a completely new gas cap..

Thanks!!!