400ex won't run just rebuilt NOT A NEWBIE

[motomanmike]

I have an 05 Honda 400ex that I bought as a project, the piston was shot. I worked with a buddy who worked at Honda for 15 years as a mechanic, he's in his 50's and all he does is turn out quad work mostly honda's. We totally disassembled this engine, got the pieces of the old piston out washed, inspected and reassembled. The flywheel is nice on the key, checked this multiple times, Timing marks are DEAD on, T mark good, Top mark and side marks on the cam, Have spark, and fuel, carb looks immaculate. It will POP Vrrrr and crank, here is a link to what it sounds like on Youtube if you can't find it search motomanmike and you will see my videos.

http://www.youtube.com/watch?v=VU3khSWYwBY&context=C3620931ADOEgsToPDskIRqoCm2ROesLWnzoqOaW0B

I hooked a old school timing light up to it and when it pops is almost seems like it looses its fire. Everything mechanical is dead on and that doesn't change obviously. I've checked all wires, plugs, diodes, etc. Changed plugs numerous times. Neutral light works, starter button works. I swear we have checked timing 5 times, rotated a tooth to be certain and rolled it back, its not timing. Compression is 120 dead on cold, as with a new STOCK compression Wiseco piston so no worries there. Valves are properly adjusted. The guy i'm working with isn't your run of the mill mechanic, i've never stumped him in 30 years we worked on this thing NON stop for 2 days 8 hours solid each day. Everything seems perfect, but it won't run. I bought this as a project and its driving me insane :) HELP. I've built too many quads to remember over the years and never had one stump me this bad. I own six quads 4 of which are over 20 years old and run perfect. I'm totally at a loss. My only thought is stator because it was in the frame, and the motor in boxes pieces when i got it and it sat out side exposed but everything looks clean inside on the surfaces and the pick up. It doesn't look like christmas cranking it in the dark so i don't think a wire is grounding out under the voltage pressue after it pops but i'm not certain. I really have thought of almost everything i can but obviously not what i need. It does act like its losing fire right after it fires up, it will fire, we pulled it and it fires enough it warmed the motor up but it just won't run when she pops it lurched i almost ran into the back of my tow and it would fall on its face, Sorry so long but i'm trying to be as detailed as i can about what we have checked.

[djwilliams0822]

O turn the fuel switch to on
:D

[gojk]

Have you checked to see if it is getting fuel? What happens if you try and start it with starting fluid?

[caseywoods5]

yeah man for sure, check to make sure you're getting good fuel flow from the petcock to the carb, try adjusting the carb a little, try starting fluid and see what happens, is the air filter clean? (or does it have an air filter?), is your air/fuel screw adjusted to 2-2.5 turns? if it is all the way in then that can keep it from running. just throwing ideas out there. hope this helps!

[hybridracer686]

does the thing have an after market cdi box that could make it not want to fire when cold. but it will spark just wont ignite the fuel?:confused:

[motomanmike]

I know its getting its fuel right because i checked 2 ways, one i put my hand over the back of the carb and cranked it, it totally soaked my palm, two i pulled the spark plug after cranking it with the ignition off, slung the plug towards the shop floor, it had gas on it, put the plug back in, crank her, she'd pop a few times, crank pop a few times crank, pull the plug and its dry as a bone. It cranked enough towing it that it warmed the motor up hot like it was running almost. Very odd one. As far as the CDI everything is bone stock bone bone stock. I have another 400ex, its an 02, do any of you know if the stators interchange? My thinking is two fold. The stator cover was left plugged in the harness and the side cover was in the frame out in the weather for awhile when the bike originally stopped working, the idiots put the oil filter in backwards and it seized the piston. Would a stretched timing chain cause this symptom of not running??? The bike had to toally have siezed at speed because the piston looked horrible and my thinking is the chain may be stretched too much? The rest of the motor was inside apart in boxes. This thing is so close. Help guys, the guy i'm working with is like my own personal Pappy and he's stumped. My only thought was to take the stator off my good 400ex and try it on this one but don't know if they interchange. I really appreciate all of you reading I really do :)

[motomanmike]

I forgot to mention i did try spraying starting fluid with the same result.

[powerbomb400]

Did you check the pulse going to the coil? That should tell you if the stator and the pickup are working. You said it had been in the weather could the coil not have a good ground.

[dxcody]

Is the plug brand new?
Alot of times once that plug gets soaked in gas it goes bad.

After i rebuilt mine, i put a new plug in it but i think i had to turn it over so many times that it fauled the plug and when i replaced the plug it fired right up after about a month of stressing over why it wouldnt start.

[motomanmike]

I've come to the conclusion it is an electrical issue. Is there any way to test the stator, it almost seems like part of it works part of it doesn't, i'll post another video on youtube tonight of what it sounds like. I know the flywheel is where it should be i've pulled it and replaced the key 3 times to be certain it was seating well on the crank.

[powerbomb400]

You should be able to check it with a volt meter. Not sure what it should read. I had a dirtbike that had some of the same symptoms and the stator was bad.

[motomanmike]

I've ordered anothers stator and coil, i'm going to replace them both i'll let everyone know if it works. Still at a loss.

[400exshop]

you may want to try you valve clearance i had my new build do the same thing....i bet we pull'd it apart 10 time's checking it from timming to key way to valve leak,,,,you name it we check'd it but we did not check the valve clearnce....lol we keep the same cam so we did not think we needed to check it....but the base and head gaskets are never the same thickness every time so it put us to tight on the valves letting it leak by just a lil...

[motomanmike]

Valve clearence is dead on 4 intake, 5 exhaust. Ok, i've been doing some reading and thought about it, I don't remember ever seeing the pin and spring that are supposively in the head for the stock decompression. I see the decompression clutch on the cam, but i don't remember a dowel ever being in the head, also keep in mind this was a basket case build, boxes of parts and i'm certain it wasn't in the head because i cleaned everything very very well when i did it and i would have gotten very worried having an extra part like that. I spent an hour wondering what locator dowels i missed when i had 2 left over after assembly and it was for the oil lines LOL. We were both very meticulous about the build and both are very experienced. My other 400ex i can't use as a guide becauses its a 440 with a hot cam and doesn't have a decompression. Would that cause this kind of issue? Would the decompression stick? It fires and stops, If i hold the throttle it will burp and stop, vroooooommppp blaaaaahhh, crank crank vrooooooompp blaaaahhhh.

[powerbomb400]

Pull the valve cover off and check. If its a stock cam then it has to have it. Seems that it a thread awhile back they stop using them on 07 or 08.

[JOHNDOE83]

try the cdi off the other 400ex.

I had the same problem, the cdi changed everything.

maybe? try it if you havent yet, also if i put a stock cdi on my 440 it wont run at all, even if its a good one.

[JOHNDOE83]

The vid sounds like the starters bad.

[motomanmike]

It had the same result pull starting it. Not the starter. She will fire and as soon as she fires she dies. I bought 4 brand new NGK plugs last night and tried that, that didn't work. Also tried changing the CDI from my other 400 that won't fix the issue either. Strange one.

[powerbomb400]

You have tried everything electrical so you about have it narrowed down to the stator and coil. Other than that the only things left is the pickup on the stator. One other thing that is way outside the box is the ignition switch.

[hocman123]

wait before u do all the work replaceing the stater just check for the decomp and spring if u are running a stock cam with out that it will never start. but i do belive u should be able push start it with out it but i might be wrong

[motomanmike]

I looked through all the parts diagrams and I know for a fact I didn't put in that little spring and pin. This was a basket case build I bought and didn't notice it during reassembly, I called a buddy that builds a lot of mx motors and he had a bunch from replacing stock cams. If that works I'll be amazed. If a stock cam 400ex won't start because of that pin then its surely the problem thanks for the info. I didn't have time to install it tonight but will tomorrow I'll let you know how it goes thanks again.

[CJM]

Oh yea, without the decomp a stock 400ex cam will not turn over the motor nomatter how much you try. Stupid design by nature, its a stinkin little spring and pin thats it..

[powerbomb400]

Its probably a design from the dirtbike days when you had to kickstart the motor.

[motomanmike]

Its eating me up at work, I can't wait to get home and try this. I know its not in there, I didn't have any parts left over from this build and it literally was a basket case, motor in boxes, and bare frame. I'm sure it got lossed being moved around before I bought it. So does the decompression stick when it revs or something with this out? Or does it just make the decompression not work? I still can't understand it because when I test compression i've got 124 psi cold but a compression tester doesn't fluctuate, it holds and then you hit the button to release it. Strange I can't wait to try it, glad i could find one before the holdiays with shipping and all being delayed on everything.

[Honda5]

I think it's just the oppisite of CJM if I recall the 400ex ones always decompress unless the spring and stopper are there to stop it. so the bike would crank good but not build enough psi to run. But I could be wrong. Let us know.

[motomanmike]

Thanks a bunch can't believe a part that small would stump me for a week. Can't thank you enough. Amazing

[Honda5]

Did you put it in and try it? What part of the shore are you from? You might have raced aginst my son.

[motomanmike]

Yes I put the spring and plunger in and it runs great! Thanks for the info!! I'm from near Salisbury. I haven't raced in about two years I had a knee replacement from a wreck at tomahawk who's your son and what class did he run?

[Honda5]

I know you. I'm Dave (991) in 40+ my son is Steve 259 on the Hondas I was there for your bad crash at tomahawk and the one at Seaford.

[powerbomb400]

It good news to hear that you have it running. Now to go downstairs and do a brake job.

[CJM]

GREAT!

[motomanmike]

Dave I really appreciate your guys help that day hope all is well. I still have your number in my phone I'll give you a shout sometime. Keith hooked me up with the parts he's always come through for me and he's still getting faster

[motomanmike]

Dave I really appreciate your guys help that day hope all is well. I still have your number in my phone I'll give you a shout sometime. Keith hooked me up with the parts he's always come through for me and he's still getting faster

[05DodgeDakota]

That don;t make sence that thats what was causing it not to start. The cams and head are the same in the 08+ motors but there is no longer a sprign and plunger for the decomp system. That had me running in circle for awhile.

It's not even needed: I'm running a 12:1 and it cranks easy with the stock starter and battery

[Honda5]

I don't think the cams are the same. I think they did away with the decompression on the later ones.

[05DodgeDakota]

no, I just took mine apart. The srping and plunger are gone now in the 08+ ones but the decomp lobe on the cam is still there. BUT, the cams are two different part numbers. Looking at exploded diagrams of each and there are some a small difference.

[powerbomb400]

I would think that since the 400 motor was on dirtbikes that didn't have electric start. Try kickstarting one without it.

[motomanmike]

As hard as it is to believe that will make it not start