400ex wont start when warm?????

[Bigbadfords]

can anyone explain why my '05 400ex will start right up when its cold but once you ride it for a few minutes and it warms up, if you shut it off it wont start back up. I just installed a stage 2 hotcams and rejetted. Any suggestions would be greatly appreciated. Thanks everyone!!!

[underpowered]

sounds like your valves are to tight. once it warms up, your valves expand, causing them to tighten up and lose compression, so it won't start. loosen them up a bit and see if that helps.

[Bigbadfords]

That makes sense, I will try that and see what happens, thanks a lot for your info man!!

[mgraff400ex]

it's also possible the type of fuel you are running. alcohol based fuels tend to vaporize easier causing hard start issues when warm. and now with your stage 2 you lost you compression release so just something to think about

[Bigbadfords]

I actually only run 92 oct. in my 400. I guess there wouldnt be any need for me to run any higher with the stock piston and bore, right?? Thanks.

[400exrider707]

Originally posted by underpowered
sounds like your valves are to tight. once it warms up, your valves expand, causing them to tighten up and lose compression, so it won't start. loosen them up a bit and see if that helps.

No that actually makes no sense. How would the valves being to tight cause compression to go down? It would raise it if anything.

[Bigbadfords]

it may seem like it makes no sense but if you really think about it, it makes a lot of sense, if your intake valves are expanded you surely wont have more compression, you would get less. I just called hotcams earlier today and their tech support told me the same thing, that my valves are too tight.

[250X_project]

Yeah, they mean the valve lash is too little, so the valves are open more than they should be and let out compression.

[underpowered]

Originally posted by 400exrider707
No that actually makes no sense. How would the valves being to tight cause compression to go down? It would raise it if anything.

not quite. if the lash is to tight, the adjustment at the rocker arm, it will cause the valve to open to soon, or possibly not close at all causing a loss of compression.

[Toadz400]

It's possible that your pilot is too rich causing it to start up in the cold and not when it's warm.

[400exrider707]

Originally posted by underpowered
not quite. if the lash is to tight, the adjustment at the rocker arm, it will cause the valve to open to soon, or possibly not close at all causing a loss of compression.

Well this is correct but thats not what he said. He said the valves were too tight. I guess I just read it wrong, but yes they will expand with the heat which is why you should be running .005 clearance on intake and .006 on exhaust, sorry for the confusion.

Originally posted by Toadz400
It's possible that your pilot is too rich causing it to start up in the cold and not when it's warm.

I would think this is more likely than the valves. If it was a car engine, I'd recommend you look at your vacuum hoses. Not sure the EX carb has vacuum hoses.

Wouldn't tight valves mean yer headed toward engine failure? If they are tight enuf to make the engine not start, that means serious friction, until they eventually seize.

[Bigbadfords]

I sure as hell hope its not headed toward engine failure considering my bike only has one year of riding time on it!! I am actually in the process of checking the valve clearances, the specs I got from hotcams is .13 on the intake and .15 on exhaust for the stage 2 cam. So I am going to recheck the valves and let everyone know what I find out!! Thanks for everyones input!!!

[250X_project]

Originally posted by garandman
Wouldn't tight valves mean yer headed toward engine failure? If they are tight enuf to make the engine not start, that means serious friction, until they eventually seize.

It's not as the valve stems are tight in the guides. He simply worded it in a confusing way. There is not enough clearence between the valves and rockers.