Need some advice on my 400ex!!

[400exmatt]

I have a 2001 400ex and it wont start. I jus got it rebuilded and basically the motor is brand new.When i try to start it just hits but wont start. The carb has been cleaned, the cdi has been switched, its in time, does anyone have any idea what this might be.

[bansheemorphine]

does it have fire?

[400exmatt]

Yes it has plenty of fire, im guess it may be the stator, coil, or maybe wiring harness, i have a harness on the way.

[400exmatt]

The reason i had to rebuild it is because i was goin bout 50 and my motor would shut off and come back on, it kept doin that till it died. My piston like melted in the cylinder. But i know the problem isnt in my motor.

[400exmatt]

any help would be greatly appreciated.

[DieselBoy]

do a plug check.......... if its wet you got fuel if its dry your not getn' the gas.

[400exmatt]

already did thAT

[tj_escott]

Here is something for ya try putting the stock cdi box back on

[400exmatt]

I Bought a new stock cdi and it made no difference. This quad has been in the shop for over a year, and they still cant find the problem.Imma bout ready to junk this thing.

[Flyin-Low]

make sure its fresh gas, the spark plug is clean and sparking, leave the plug out and crank it over a bunch of times, make sure the battery has a full charge then giver her a whirl... but other than that try puttin the old cdi box back on just to try it out cause maybe the new one is faulty!

[Old Head]

This quad has been in the shop for over a year, and they still cant find the problem.Imma bout ready to junk this thing.


Wow time to find a new shop, Does it do anything when trying to start like backfire out the carb? If so your time might be 180 out. I'd check the grounds too and make sure your getting all the proper voltage outputs.

[hondaguy2]

Its more than likley timing. I rebuilt engines before and it will run but missfire or run for a little while and quit or not start at all. Its a very easy thing to look over and if its off by just one tooth it will run horrible or not at all so double check timing just a thought.

[northwest Texas]

When I rebuilt mine, we couldn't get it to start and our problem was with the valves. I thought we had them set right but they were still too tight and when we readjusted them, she fired right up.

[400exmatt]

The valves and the head is been adjusted.

[DieselBoy]

is it possible you put the piston in backwards?

[nxkustoms]

the problem is that the right front exhaust rocker is setting the wrong part of the decompression part of the cam. If you adjust your vavles and losen the valve adjuster all the way the set it at .004 of an inch it will start but nock really bad. thats as far as i have gotten but there is a way to get back to normal.

[400exmatt]

I found the problem when I took it apart i left the cam setting plunger and spring out, and when the shop put it back together they didnt notice it was gone, and some guy I know told me his had the same problem and that was it.

[benbuilt4u]

Originally posted by 400exmatt
I found the problem when I took it apart i left the cam setting plunger and spring out, and when the shop put it back together they didnt notice it was gone, and some guy I know told me his had the same problem and that was it.


does anyone have a picture of this??

[400exmatt]

HUH?

[m/key]

a picture of the plunger? look in your manual, there will be a photo description of the plunger and spring.

[400exmatt]

here ya go

[400exmatt]

another.. Spring

[400exmatt]

That Help?

[benbuilt4u]

Originally posted by 400exmatt
That Help?

thanks so much!!! i think i was missing that!!

[400exmatt]

YW

[josiah400ex]

another useful thread.......good info.

[400exmatt]

Im so glad i found the problem I've been buying different parts trying to fix it for over a year.