Hey folks, this is my first post/thread so go easy on the new guy!

I recently bought a 1999 400EX with the 440cc kit, hot cams, and a White Bros e-series slip on pipe. It had a broken swingarm, so I got it cheap and replaced the swingarm with an ebay unit. The bike ran great in the parking lot at my office. We probably put two hours on it there, trouble free.

So, thinking the bike is ready to go, we toss it on the trailer and head to the dunes. It starts right up fine, but after about 30 seconds it won't idle. We can easily keep it running with the throttle, however, so we head toward some big hills to climb. The 440 makes it up a few hundred feet, where suddenly the motor kills. We turn it around and it fires right up. Second attempt, the same result. So we head for flatter ground and make it about 1/4 mile when the engine again stalls... only now we can't get it to start again. I'm thinking fouled plug at this point, so we pull it back to the truck and pull the plug. It looks good, so I lay it against the motor and crank it over. Spark plug is throwing a strong spark. So, we move on to the carb, pulling the main jet. The jet is clear, the bowl is clean, fuel is flowing nicely from the tank. We gave up on it at this point and just took turns riding the rest of the bikes.

Today, my dad (great mechanic and unbelievable problem solver) and I tear into the thing. He says the spark looks a bit weak, so we replace the plug. Still doesn't run - no sputtering, no backfiring, just endless cranking. So I trade coils with another 1999 400EX which runs fantastic. No change in the spark. We re-gap the plug to .021" and the spark improves, but still the engine does not start. We try starting it on starting fluid - directly into the carb... no progress, still just endless cranking. So, we take the gas tank, plastic, and valve inspection caps off to make sure the valves are moving. They are moving and appear to be timed correctly. We then drained the tank and carb and filled it with brand new 91 octane gas. No change. Finally, we tried to pull-start it with the truck. We did manage to get it started, but it will only stay running with 1/2 or more throttle and at high RMP's. It runs awful, but does not backfire or anything strange. It does hesitate when you crack the throttle, which would lead me to believe it's lean. I do know the accelerator pump was working in the carb.

So, I'm stumped. One day it's running great, the next day it's crap. The coil is fine, the spark plug is new, it's getting fuel, it's getting air, it has spark, the valve train seems fine, and it has great compression. Any thoughts?

Thanks,
Jared

Try switching out the CDI box with that bike that you swapped the coil with.

Has there been any major weather changes around there?

Whats it have for jetting?

Stock Carb?

Elevation, Location?

-Kip

i would look into the timming a little more. i had a simailar problem this summer when it wouldn't run then run fine then it just lost all power. I checked everything like you did too and was stumped. I tore it apart and relized the cam chain skiped a tooth. My cam chain stretched and the tensiner was junk. With being that big of a motor you might have a manual chain tensioner.

Also make sure fuel tank isn't plugged with crap. That also happened to me. Lol

i got a 2000 400ex and they like the attention.Trust me

hope it helps
Brandon

The CDI box will be the next thing I try because it's simple... though I'm doubting that's it due to the good spark. As far as the cam timing goes I have not torn deep into the motor to verify correct timing. We just found TDC and watched as the valves switched from exhaust to intake at roughly TDC. I'm assuming to verify the cam timing you find TDC, then look for some mark on the cam that corresponds to a mark on the head at TDC... with a similar mark on the bottom sprocket? How much of a PITA is it to check the condition of the chain and tensioner? Just pop the right hand case cover? I'm also having doubts about cam timing problems, because the problem was intermittent at first. It worked then stopped, worked then stopped, worked again then stopped for good. It's making me think it's an electrical problem.

Location is northern UT, elevation is roughly 4200', weather is steadily cold. I just bought the bike a while ago and only have a couple hours on it. I'd never been in the motor (or any four stroke bike motor for that matter) until this one crapped out.

Fuel flows freely, tank is clean, has in-line fuel filter that flows great, carb bowl was clear as was main jet. Carb is stock, jetting is unknown. What's stock jetting anyway? Also, forgive my ignorance, but where/what is the pilot jet? I've run a 250R for years, so the four stroke quads are new territory for me and I've never had trouble until now.

Thanks for the help so far guys!
Jared

Hey I have a couple thoughts

Pull the stator cover off. make sure the pickup coil is intake. Make sure the stator looks ok. I have seen them have Issues if ran hot. I had a 440ex exact same symptoms. first thought pilot was plugged cause it would not idle. cleaned that. Also make sure oil level is not too high. The heat cannot dissipate when case is too full.

What is the valve lash?

Sounds like a carb Problem to me I ran a Edlenbrock Crab on Mine so I don't know mush about the stock carb but I do know it sounds just like a clogged carb.

Kinda a small thing that you may not have trouble with in the dunes, but check the vent hose on tank cap. I have seen several of them get clogged and the quad would run fine for a while, but then after it started draining the gas from the bowl would stumble. After sitting a second would start right back up.

Pilot jet is right by the main, it is recessed a little and you will need a flat screwdriver to get it out.

To check the timing you will have to remove the valve cover. There is a plug on the stator side on top, remove it and line the mark up with the T on the flywheel and then when you take the valve cover off and look at the cam gear you should see the marks on it. They should be even with the top of the head if you are looking straight at them.

What is your jetting, and does it have an aftermarket kill switch or maybe used to have one? I have seen people take them off and then leave teh wire hanging and it would ground out while riding and kill the motor. Hope you find the problem.

I would try the CDI box my buddy had the same problem just one day in wouldn't start, he put his stock CDI on and it fired right up and worked fine

Could you explain this further?


Okay, I'm assuming now the pilot jet is the "idle" jet... correct?


I'm guessing this would be the clearance between the lifter and the valve when the engine is cold. I don't know, I have not checked. Got a spec for me? It has the stage 2 hot cam with unknown valves. Valves are likely stock.


Thanks for the info.


Unknown jetting at this point, but I will check it and post it up. What's stock?
The kill switch is factory... though the plastic slider is busted off. It's stuck in the "RUN" position, but can still be moved with a screwdriver and seems to function as intended.

Jared

valve lash- set cold-

intake: .13mm, .005 in

exhaust: .15mm, .006 in

if the slider on the kill switch is broken off, i would look into that first

hope this helps

If this is the case as you said.

So, I'm stumped. One day it's running great, the next day it's crap. The coil is fine, the spark plug is new, it's getting fuel, it's getting air, it has spark, the valve train seems fine, and it has great compression. Any thoughts?


I would like mentioned

Check timing, or valve clearance


It can be out of time & still have good compression

If valve lash or clearance is no longer & its holding the valve open your compression should be lower & keep your motor from starting.


If you are getting good spark! I would not worry about any electric issues now.

make sure you are not getting too much gas?

My money is on the CDI box.

I thought I'd update this. We checked compression today and it was a whopping 40 psi. We adjusted the valves, which were just a bit tight but it did not change the reading at all. I'm thinking it's time for a rebuild. This motor is probably 20 hours old since the 440 kit according to the info from the previous owner. K&N filters stink!

I'll keep this updated as I discover more.

Thanks,
Jared

[quote name='DeadEye J' date='Apr 16 2009, 06:08 PM' post='676201']
I thought I'd update this. We checked compression today and it was a whopping 40 psi. We adjusted the valves, which were just a bit tight but it did not change the reading at all. I'm thinking it's time for a rebuild. This motor is probably 20 hours old since the 440 kit according to the info from the previous owner. K&N filters stink!

I'll keep this updated as I discover more.

Thanks,
Jared
[/quote worn out with only 20 hours on it ? sounds like the guy you got it from was flinging some BS, good luck with the rebuild, Steve

if you built a 440 and did not put the new head studs in it you will blow your head gasket... you pretty much must put in the new stronger head studs..

It should probably have a higher compression reading then that but you cant check cranking compression on a 4stroke engine because we have decompression releases built in. My money is on blown head gasket or something with valves...worn out or out of adjustment...or out of time. Actually I bet the timing is off

This happened to me. If you're doing a top end, it is a MUST to put these in.

I finally tore this baby down for real to discover the root problem. Yep, it's compression related. There was probably a teaspoon of fine to coarse sand in the top of the cylinder and baked onto the head in the carbon deposits. I would advise anyone who reads this to never, ever, ever run a K&N air filter. Telling yourself it's filtering, even with a prefilter, is just a lie. I'm 99% sure the sand killed it!

The piston obviously got hot. The aluminum is smeared across all the rings on one side.



The cylinder... note the dime sized patch of aluminum stuck to the cylinder wall near the bottom.




The head. This looks very dark/black to me. I'm a 2 stroke man, but this says rich fuel mixture all over it!


Needless to say, it's time for a rebuild. Is there an oversize piston for the 440cc kit? I haven't been able to find one.

Jared

NO they make one that is 89.5 but you do not want to go that way. Just Re sleeve it and call it good. Hey man it's not the filter it's the intake boot, I had these same problems with both my Honda's. Sometimes the boot gets a little lose when your riding it and don't know. I put a 400EX Velocity Intake with K&N air filter, air intake on mine and never seen one pieces pass the filter sense. I have the same motor in my 460 ex I just stroked it and I ran it for hurs, than sold it to my brother and he ran it for hurs. We always had comp never had any problems with anything.

Now it could have been the head studs, you could have been pulling sand into the head gasket i seen you did not have HD head studs. Do you know where to find them, if I was you I would get to looking before you put it back together.

There a 450r stud and need to be done by a pro.

I found them on GT Thunder's website for $59.95 http://www.gtthunder.com/)
E-bay
400EX Velocity Intake with K&N air filter
In-Stock, Ships UPS Ground Tomorrow M-F Buy now$84.99 Shipping $11.75

let me know.

Also they make a HD timing chain that I but in mine, stock ones will brake!!!!!!(taking out the top end)

Use a crf450 timing chain, same as the heavy duty chains sold by other companies and a lot cheaper.

Well, I ordered a new piston and sleeve kit from rockymountainatv.com, which already puts me over budget on this rebuild. I'll be cleaning up the valves and using the same timing chain again. I really don't think there's that many hours on this build, just sand in the motor wiping things out prematurely. I know that 3/4 of you will call me a cheapskate because of this, but this is a spare bike and I'm really not worried about these parts failing. I'd love to have a ton of extra cash laying around to put a HD chain and a 3 angle valve job on this bike.

So what's the weak link with the stock head studs? Do the studs actually stretch or do they pull/deform the aluminum threads in the cylinder? The larger 440cc sleeve looks to be installed right up against the head studs. Is that what causes the problem - i.e. the removal of too much aluminum cylinder material around the head stud thread area?

If it's just that the head studs themselves are too weak... just a 12.8 grade bolt with the head cut off (and cut precisely the correct length) should do the trick. Throw some high strength thread locker on the bottom for good measure and call it good.

Thoughts?

It is not always just the studs, I think most times it pulls the threads out of the cylinder. The crf chain like I mentioned is like $35. jmo

duke416ex
is that any year crf450 i need to replace the chain in my 400ex

Any year CRF450 chain (I used an 02) will work, up until I'd say 07, I'm not sure beyond that. Service Honda cost me about$35shipped to my door for the cam chain. Its the same most big builders sell for $115 or whatever.


Though I agree with your K&N results and the sand getting in, my best guess is using the wrong fuel for the build. A 440 will generate a lot of heat, and proper fuel needs to be used to prevent detonation and pre-ignition. This improper use of fuel causes even more heat, thus breaking down the aluminum in the cylinder, and thus why you see so many headstuds pulled out of the heads...

On a 400ex, I would always put the CRF cam chain in anytime a rebuild is done... if going 12:1 compression or higher I'd use a HD rod and HD headstuds... just my thoughts on the subject...

Yeah I'm telling you these are two thing you do not want to pass up.

Hey I know about budgets, but I'm telling you let is set for a anther week or two until you do have to money. Did you look at the intake boot, and did it have sand in it. With that much sand in the top end it can't go though a K&N filter, there's only one of three ways: filter had a hole in it, intake boot was lose, or this is what I thank it got in there through the head gasket. Everyone of these 440 that i know of put the HD STUDS in there you will pull them OUT. It's not that the stud are weak it is the treads that are weak. When there install YES they will be right next to the sleeve, that's what happens when you bore a cylinder all that way. Your at the limits of your bike and you can't bore no more that's way everything on the cylinder looks so close, it is.

Get the chains and the studs!!

It's like this you just went over budget right, Will how are you going to fell when it dose the same thing again but this time the chain breaks and take the value train?

It is in your best interest to spend a 120.00 more dollar IT WILL BE CHEAPER IN THE LONG RUN!!

Hey one more thing you bore could have been egg shaped not saying it was!! I had a old guy at a machine shop in Manhattan bore my 440 out the first time and I had problems during break-in. Took it a part and it had the same wear on one side of the piston than the other side like your pics. just make sure who ever you have do it take there time to measure things.

Wish you luck let me know I do know a lot but these 440 and 460 kits!!

I have always used the 02 also, but I think most years are the same. Jus make sure they have the same number of links as the 400 chain. I think maybe even the 450r chains are the same.

after looking at the pictures.. I can not say that that was because of sand... looks as if it got hot causing the gauling.. IMO I Think it could have been lean and that caused the issue.. this could have been from different reasons but the way it is only on one portion leads me away from sand.. again just my .02

I will likely go this route. Thanks.




This was (to the best of my knowledge) built with an 11:1 piston. I was under the impression that pump gas was typically good up to about that point. Timing should be stock as near as I can tell.

Can a slightly rich jetting be used to keep things a bit cooler? I'm beginning to think all the black deposits on the head were caused by burning a little oil rather than a rich fuel mixture. It's as likely to be jetted lean as it is jetted rich.



I get the whole ounce of prevention thing and I understand that the head studs are a weak point. I'm sure the HD studs are a sound investment and will likely eliminate any potential problems with this in the future. However, it doesn't end there - you have to have a machine shop drill and tap the cylinder to accept the new studs. I was quoted $215 to install/bore the sleeve today, so adding in the $275 I've already spent I just hit the half-a-grand mark when you include tax. That's without the fancy studs or new chain. What I'm exploring here is a budget oriented option.

Has anyone had success with HeliCoils in the cylinder? They would about double the surface area of the threads in the cylinder which should double the holding strength in theory. Add that with some M12.8 bolts cut to length and you should have a very strong setup for less than $20, plus you can do it in the garage for zero dollars in labor. I just don't know if there is room for the larger diameter of the HeliCoil with the sleeve being that close to the studs.

I'm even considering installing the sleeve myself to save the $180 labor. Yes, my dad and I have done this at home before on a Suzuki LT230. Yes, we have mill and a boring bar to cut out the old one. We could even bore it for the piston, but for $30 I'd rather have it done by a professional shop.

11.1 should be fine on pump gas, but on premium. Running to rich can be bad for the motor like running lean, but I would say the biggest thing with rich on a 400 is loosing a lot of power. With a 440 it is crucial to keep heat down. Many people install bigger oil coolers, this is not hard and you should be able to find a write up on exriders.com Also, always use a good oil.

I would check the boot too. I had a 99 for years, when I did my rebuild the rubber on the intake boot had seperated and was letting water and stuff in, but I caught it before any damage was done. The later years had a better intake which the rubber completely covered and didn't come loose from.

If you feel confident changing the sleeve I say go for it. I would think if you have the equipment the head studs would not be hard to install either. I haven't tried helicoils on the cylinder, but have used them to hold the valve cover on with no trouble. I would say there is plenty of room to install them, but if I had the choice I would rather have the heavier studs. I was thinking you could find them for under 40 bucks but can't remember where.

I have built two 440EX's in the past and nothing but problems with them. The best luck and best performance I have gained is with a 416cc and a 426cc ex build. My sons 426 11:1, stage one cam puts a lot of 450's on the trailer first round.

Get your piston ceramic coated and get the skirts dry film coated. www.cradin.com does all of my pistons.

Well, I decided to bite the bullet and have the sleeve installed and the cylinder prepped at at cost of $240+tax. Much to my surprise, my cylinder head bolts have already been helicoiled in the jug! I'm going to re-use the stock head bolts, as the helicoils already have as large of a thread area as the HD head studs. It shouldn't cause me problems.

Anybody know of a good writeup with photos on rebuilding the top end of a 4 stroke?