trx 400ex will not start

[scottsrepair]

i am looking for some help with a 400ex cant get this thing running . the carbs clean good spark adjusted the valves flushed the gas will not start on starting fluid . my question is there a low oil sensor that will stop it form starting . is there a key on the crank that could knock the timming out . any help would be great thanks scott

[Honda#4]

never use starting fluid, you will see your rings go right through the head. To answer your question there is no sensor thing on a 400ex, did you check the battery or put in a new one? Does it turn over at all? There is a woodruff key or A.K.A the timing key on the shifter side of the motor maybe it broke or is wore out but the motor would still turn over.

[scottsrepair]

yes it turns over and backfires once in awhile do these keys break often and i do have spark good battery drained fuel and put new in anyhelp would be great thanks scott

[Honda#4]

I've never heard of a timing key breaking before but you never know, sense it turns over and backfires then it ain't your key. What does it have for mods? Do you know the jetting it has right now? Have you done a compression test on it? Is it bored or stroked? When you turn the bike over for however long it can run what does the sparkplug look like?

Sorry for the funny questions but it's helping me figure out what it is. I never heard of this problem before, but don't panic I'll figure it out.

[scottsrepair]

hi thanks for your help , it is bone stock and it just stalled one day and the cust said it was hard to start got it running to get back to trail but didnt run well and didnt start since . when it back fires it only dose that as i try to start it . it never runs hope i explained this well thanks

[JOEX]

Compression check?

[Honda#4]

Maybe put a bigger pilot in, I think it has to do with the carb the motor to me seems fine. Maybe adjust the air/fuel screw?

[scottsrepair]

hi well after much work today took carb off and cleaned it again make sure i didnt miss anything adjusted seems to be ok if i crank it over and check the plug its wet if i pull it after a backfire its dry . soon going to loose my hair . and the comp. is with in spec .

[Honda#4]

Ok put in a 42 pilot and maybe a 150 main jet then it should run I think, but it is your carb though so now we have it pin pointed.

[scottsrepair]

ok ill try this but i , one thing that bothers me is that it ran one and not the next with nothing other than the day has changed .

[Honda#4]

Yea try what I said, Did you ever check the float on the carb it may seem that it needs to be replaced, that's what maybe is causing your wet plugs.

[Which 450?]

is the gas on? One trick I used is to take the airbox lid off and the air filter out, then cover the entire air intake with your hand. as sort of like a 100% choke.

[scottsrepair]

yes the gas is on and i have the air box completly and put my hand over the carb. this thing is driving me nuts it should run . i was working on it again today and found that it would back fire if i hold the thorttle wide open and crank for long peroid of time. i did change the jet but nothing no change . at this point im guessing either the key is split on the crank and it's out of time or i got a bad cdi box but i do have spark. or got a problem with the comp. release . thanks for the help any is good

[Bigbadfords]

well I think we got it pinpointed to either compression or timing, which kind of go hand in hand, so maybe that will make things a little easier for you. Good luck!!

[Honda#4]

It's got to be the timing is advanced or something, if you have spark I don't think it would be the CDI. I'm betting money that it's the comp release mechcanism.

[Which 450?]

I'd put a negative on the compression release, you don't need that to start. I had an after market cam in my old 400ex and it didn't have the comp release on it

[400eXr1d3rZ]

Is it getting fuel? Bad fuel?

[CRE Performance]

I ran into the same problem on a 400 EX once. The owner had cleaned the carb while the engine was torn down and being built, once back together it wouldnt start but it sure fouled some plugs and did some backfiring.

What I found was this....When he took everything apart, he blew it out with air. There is a piece in the carb known as the jet needle (not to be confused with the needle jet) that usually stays in the carb when the main jet and the main jet holder is removed that the needle slides down into. THIS WILL COME OUT! It had been blown out and reassembled without it basically fuel soaking the engine when starting it. It was siphoning right out of the main jet well. I looked at this carb 5 times before I finally noticed it missing.

[Honda#4]

If your refering to the needle that can't come out by force of air cus it has a clip on it. The needle jet is alittle tiny thing about a 1/2 inch long not even that the needle goes into, if you have the float bowl off and you open your throttle this will fall out cus when I jetted my bike I had the socket on to far and I unscrewed the main jet holder and the needle jet fell out on the ground.

[CRE Performance]

Originally posted by Honda#4
If your refering to the needle that can't come out by force of air cus it has a clip on it. The needle jet is alittle tiny thing about a 1/2 inch long not even that the needle goes into, if you have the float bowl off and you open your throttle this will fall out cus when I jetted my bike I had the socket on to far and I unscrewed the main jet holder and the needle jet fell out on the ground.


Yep, the needle jet. Most of them are tight and tough to get out but some of them are loose. If you are unaware that it is removable or will come out, you will more than likely loose it if the carb is apart with the main jet holder out.

[Honda5]

I'm going to guess that the cam chain jumped a tooth or two. I have had a couple of cam chain adjusters break the spring. Pull the cam chain tentioner out and check it. If it is broken get a new one, reset your timing and go from there. if it is good see how far you can put it back in (easy!) to see if the chain is streatched out past the limit of the tentioner. If the chain is streatched out bad it will make it harder to start and if it is real bad it will jump over the gear.

[Honda#4]

I'll tell ya what that needle jet is hard to find if you lost it when you jetted your bike, I lost mine at night when I jetted my bike the first time, boy was that scary. I did'nt even know what it was untill I looked it up in my manual. So I ended up fliping my carb over to push the thing back up in the carb. But after all that mess and ripping stuff apart it started up I was so glad. Let me tell you im a lot more cautious when it comes to jetting, you always have to keep an eye on what your doing.

[scottsrepair]

ok guys i found the problem just like i was told the cam jumped a tooth and the tensioner is all the way out . after taking the rocker cover off also found that the engine looks like it was run low on oil the center of the cam is glawed going to segust a complete overhaul to the cust. again thanks for all the help scott