Good info!!

Are you trying to start it now without the air box also?

The main jet shouldnt be an issue at idle, but once you slap that throttle it comes into play as well as the needle and slow/pilot jet. My thinking is that if the previous owner went with a larger main jet he also may have messed with the others as well, and even though you cleaned it up (there are different ways to do this also) it may still have too much jetting as well as other problems like junk that remained after cleaning, sticking floats (good call asfa) or even a bad float jet.

Also even though the various jets are thought to work at different throttle positions there is a relationship between the needle and main jet as a larger main or smaller dia needle will allow different amounts of fuel to pass between them within their normal ranges. There have been issues with higher modded engines running the stock carb due to the larger mains needed for the upper throttle positions causing the lower postions regulated by the needle to become too rich at the proper clip setting. It can get a little indepth but what I have found is to never discount the carb as a potential cause of running problems.

I hope that helps

 

Did you measure your cam chain to check and see if it was stretched when you were in there. Sounds like you have a buddy with an EX. I am wondering if a cam chain issue was what caused the damaged spring. If you wanted to for sure eliminate the coil issue that should only take you like 10 minutes to swap. You said you are getting fuel but I am still curious if you open your drain does fuel keep draining out rapidly or not. I don't think this is the issue but I am just curious how you determined you were getting fuel. This sounds like motor/timing/cam chain issue but it would be nice to for sure eliminate a few other things before going back in.

 

Check the choke cable closely, work it while looking at the cable. Make sure it is not loose at the carb. I found a small crack in mine once at the carb...Another thing to watch on the carb is pull off the bottom of your carb and make sure the metal tab on the float shuts gas off the needle jet. The tab sometimes needs a little bend to fix flooding and aat

 

Guys, I could be way off base on the spark thing but I don't want to see somebody go through so much hassle just because something simple was overlooked. Swapping or testing the coil is a walk in the park compared to removing and tearing the carb apart and it needs to be done to positively eliminate it from suspission. Once he eliminates it I will step down off my soap box.

Lets recap and look at the facts.
It ran apparently good for a short time but had cam chain noise so he shut it off.
Complete engine teardown was the next step and it has not run since.
It cranks over apparently sufficiently enough to rule out slow cranking.
The fuel issue was pretty much laid to rest when he sprayed a shot of carb cleaner into the carb and saw no results. That means its not a lack-of-gas issue. That leaves the question of being rich but If it was rich it would have at least atempted to fire when he installed the new plug. Not to mention other tell-tale signs like the smell of gas and a wet plug.
If we can rule out spark and carburation, the only thing left is timing. Did he time it properly when he reassembled it? It ran before but not since the tear down. Its safe to say that its not 180 out but is it a couple teeth?
We'll see I guess. Keep us informed Turbo

 

Good news gang! I picked up a working 2001 400ex this afternoon and the first thing I did was swap the coils and plug wire and....no luck (bummer). So then, I put the original coil and plug wire back on and hooked up a tow strap to my 2500HD for a little pull down the road. Much to my amazement, the quad fired right up for about 10 seconds, but then quickly stalled once I let off the gas to see if it would idle. We came to a stop and I tried to start it from the button again and nothing. So again we pulled and again it fired up and ran. Throttle response was great and the quad runs phenomenal above 1/4 throttle I'd say. But it just dies completely once you back off and the rpms drop. After towing it for about 1/2 mile (with the quad running behind the truck....--I just kept it above 1/4 throttle with the clutch pulled in), I unhooked the tow strap and drove the S.O.B. all the way back home (again keeping it on the gas just enough so it wouldn't die). It had great power and I revved it out into the top of 5th with no problems, but upon decelleration, I would just downshift to keep my rpms high enough so it wouldn't stall. So I must conclude that being it runs so smoothly during operation, my midrange and WOT carb circuit are operating correctly. Which leaves me with my pilot circuit as the culprit IMO. Cranking speed should not be the problem as I always have the battery fully charged when I try to start it. After my 10 minute test ride today, when I got back to my house, I tried to bring it down to idle and again it just shut off (dead). Shifted into neutral and tried to start the warm engine (which shouldn't need full cranking speed anyways to fire) and nothing. I'm thinking its in the carb (pilot circuit). Anyone else?

 

If I read only your last post here I would say definately pilot circuit but reading everything else that has been done in attempt to start this thing, I would say not likely. The pilot circuit deals with very small amounts of fuel, usually similar to the choke circuit. Unless the choke jet is plugged also, it should at least run better with the choke on. Did you try that? Also, spraying a small amount of either or carb cleaner should make it light off at least for a couple seconds if its starving for fuel. From the info provided, I would say that you have another issue like timing.
Congrats on getting it started though I'm officially stepping down off of my soapbox as promised.[img]i/expressions/face-icon-small-happy.gif[/img]

 

I dont know anything about the 400ex but I know my honda trx wont start unless you have it in neutral...

 

Great to hear you got it to run!!!

I bet you were like this [img]i/expressions/face-icon-small-happy.gif[/img] when it fired up.

Just for sheets and giggles next time you try to start it with the starter hook up another known good battery with some jumpers and see if it will fire up, but also pump the throttle a few times and hold it above the point that it stalls when you hit the starter button.

You should really dbl check the carb internals (I know you may be getting tired of hearing that lmao), but you also may want to carefully check how many turns the fuel screw is currently OUT, and then try turning it out 1.5 turns first and see how that effects it and then to 2 turns, and then 2.5 turns being the max. If any of these seems to help then compare it to the point where it produces the highest idle rpm (assumeing you can get it to idle) and let us known what you find (I hope adjusting it may actually give you an idle, and also the increased juice from the second battery gets her to fire up too).

Sounds like progress to me!!!

 

After writing the above I remembered somthing that maybe helpfull to think about.

My cousin had a 400 he didnt take particually good care of (what your original description leads me to think was how the previous owner was) that was having trouble starting, and as time went on he had actually permantly attached a damn rope on his bumper so it was ready for pull starting etc.

After he allowed it to get to the point that it wouldnt even pull start all the time I let him talk me into checking it out for him, and what I found was that the carb was a mess (it needed to be rejetted, and completely cleaned out) his battery didnt have enough juice to even light up the head lights well (totally dim) and when you put enough juice to it to run the starter it still wasnt turning the engine fast enough (for some reason honda set this engine up with just barely enough starting rpm, and once the battery is a little weak look out) as the starter clutch was also slipping.

Just something to keep in mind.

One last thing is if you tried starting it both with and without the choke on.

 

I agree with the checking of the mixture screw position. If its out at least 2 turns, then id say the pilot jet is plugged. That hole is so small, it doesnt take much to block it. When you get it out, you should be able to see light come thru the center hole...like looking down a straw.
From my experience it seems like when all else fails...try pull starting. If a motor can start....it will.