440ex will not rev and has no power just rebuilt it a few weeks ago

[Predator13]

Ok so a friend of mine went and bought a 400ex that he has turn into a 440. 12.1 comp piston, stage 3 hot cams, oversized oil tank, and hasa dg slip on and some kind of aftermarket header. we have 100 octane in the bike and the bike has got to be the slowest 400ex ive ever seen. it was beat by a 250 recon (no ****) it seems to run "flat" if that makes since it has no reving power and doesnt throw dirt and forget about wheelies. the dg pipe doesnt look like its the right one for the bike and the header looks werid. please help with ideas and also the carb was cleaned and gone through. Just want to get some ideas where to start. ive been reading and have found that it could be this and that but wanted to get a more narrow set of answers. any help would be awesome. and if i can supply you with any answers to questions i will be happy to help. we are just confused because we expected this bike to fly. also the gearing has been changed for more top end but only by a few teeth nothing that would casue this. its in the fuel system or motor (we think) lol

[tri5ron]

You are going to have to just start with all the basics and go from there.
You have messed with just about everything possible.

Bore, Compression ratio, Cam, Carb, Exhaust, Gearing, and who knows what else. There are a hundred questions that we could ask, but if you felt confident to tear into the engine that far, I'm assuming you either have some mechanical knowledge and experience, or you just purchased a bunch of "go fast" stuff, and hoped for the best.

Either way, you are going to have to verify that everything is doing what it is supposed to do.
Compression, Cam timing, Carb jetting, Valve settings, proper Exhaust, Intake flow, not to mention, any leaks in Head gasket or Intake boot, or pulled out studs, (fairly common for 12:1 on oem studs). Then after all of that, you need to clarify what you mean by "gearing has been changed by a FEW teeth". That could be alot.
front , rear, how many on each ?

Basically you need to start over,
(or at least start SOMEWHERE),
and go from there.
You have altered just about everything possible, and nothing is in "Sync".

Unfortunately, nobody here is going to be able to give you a quick and easy fix, until you can verify more of what is, and what isn't, correct on your machine.

There are many threads, covering every subject you have mentioned.

You would likely find a wealth of useful info., in the sticky thread at the top of the 400EX forum. Start by reading those, and go from there.

Read about the various builds, the various combinations, what has, or hasn't, worked for others.

btw- Welcome to the forums, and good luck with your machine.

[Whit11b]

Let me answer your question with more questions.

Start by checking cam timing. Make sure all your marks are lined up right. Did you guys rejet the carb? What jets are in it?(main and pilot, also where is the needle at)
Were did he get the exhaust from? If he has some screwed up setup (or have a blockage) excessive back pressure will cause problems.

Some more info on how it is running would help. Does it start and idle like it should? Any noises? Rattles or backfiring or anything?

[JOHNDOE83]

The stage 3 cam and the fact that you never stated anything about jetting makes me worried.

But if you have all these new mods, you might need a timing adjustment.

If it revs up but dont go nowhere, it may be the clutch.

We need more info...lol.

[supertrooper90]

that was my first thought too is jetting. Dont run it till you get it figured out. Check your spark plug if its white and chalky its runnin lean. The more info you can give the better we can help you.

[Predator13]

ok to answer this gearing question i worked on the bike today the only thing we changed was 15 in the front the rest we put back to stock gearing. timing is perfect. oh and by the way im very mechanical just at a loss. the carb has stock jets in it has never been messed with but i have a jet kit ordered and im going to try a new pipe for it but i wanted to know some people who were familar with these 440s. i was looking at big gun, yoshi, or fmf. Opinions? the bike has a DG full exhaust but i believe the silencer is not a 400ex pipe but the header looks good on it. but anyway the bike has good torque right at first the just dies the plug looks good to be honest. it starts perfect and idles great. plug is a nice brownish color. ive been reading about head gaskets and im starting to wonder if thats what has happened because this bike reved good while the motor was just idling and quick revs for the break in. i have a leak down tester so i may do that in the morning. also i know its not the clutch so we are good on that (new) plates, basket, and inner hub. im starting to wonder seriously about the head gasket and i think its a combo of the dg exhaust so i think after i get some opinions im going to get a full exhaust and start with my jets. also if this helps it has 103oct. gas in it. im just trying to get a starting point this is the first 400ex ive ever done so im trying to get some ideas and get a good heading so i dont waste alot of time on doing worth less stuff. thanks for all yalls help keep it coming!!!

[ae13291]

lol did you say stock jets? i dont care if your 100000 ft elevation you do not run stock jetting on that set up. go to atleast a 42 pilot and 165 main. telling us the elevation will help. also you might want to try a lower octane.

[CJM]

Stock jetting??? :eek:

It needs to be jetted pronto before it runs to long leaned out and blows!

[smelly$cat]

Originally posted by ae13291
lol did you say stock jets? i dont care if your 100000 ft elevation you do not run stock jetting on that set up. go to atleast a 42 pilot and 165 main. telling us the elevation will help. also you might want to try a lower octane.

I wouldn't worry about the octane you are using. It should be fine. 12:5-1 justifies 103 at least in my opinion. If the fuel isn't old, I wouldn't worry about it.

Jetting is the first order of business. You say it idles fine and feels good when you first take off, then it falls on it's face. I think that's your main jet being too small there.

[Whit11b]

I agree with ae13291, jetting is going to be the issue and 42 pilot and 165 main is going to be the place to start.

I have a full Yoshi stainless setup on my 450R and have been very happy with it. A friend has a FMF slip on and it is working good for him, no compaints on it. I ran an HMF on my EX and thought the quality and performance of it was very good, would recommend one. Big Gun I haven't had any experiance with and couldn't say one way or the other. The performance you will get out of the Yoshi, FMF, and HMF would be pretty similar so I would go with the one you could get the best deal on.

[CJM]

165 is gonna be to small, I have a 170 in mine and it isnt nearly as big as a 440. Id start at 190 and take it from there.

[JOHNDOE83]

My 440 uses a 220 main jet and a 50 pilot jet with a 450r carb.

Stock carb was 42 pilot, 210 main jet.

[ae13291]

he must give us elevation to determine a more accurate jet. the higher compresson you have the harder it is to get it dialed in.

[Predator13]

Well here is what ive got. i got my jet kit in friday and think im starting to get somewhere. a friend of mine has a hmf for his 400ex and im stating to like it. but any way i have jetted my carb but not sure of the elevation that im at greensboro, nc. but im at 200 main and a 50 pilot and this bike is starting to come alive. i have robbed my buddys hmf exhaust to get this things going. but i think im going to go with the hmf after i get all the kinks worked out. but im still working on the jetting so hopefully i will get her going good on sunday. but i have already ordered a full hmf exhaust. but so far its running 9,000 time better and was atcually pulling wheelies so i think im headed in the right direction. also what are yalls reviews on the rev box's? was looking into that as well. THANKS FOR ALL YOUR HELP EVERY ONE!!!!!

[supertrooper90]

sounds like your on the right track with jetting and the exhaust. Dont waste your money on a rev box. the 400ex never really revs that high to need an extra 1000 rpms.

[trxPOWER]

good deal dude! but im sorry i just had to giggle when you said this: "oh and by the way im very mechanical just at a loss. the carb has stock jets in it has never been messed with"

[ae13291]

keep your stock rev box

[smelly$cat]

Originally posted by trxPOWER
good deal dude! but im sorry i just had to giggle when you said this: "oh and by the way im very mechanical just at a loss. the carb has stock jets in it has never been messed with"

douche

[JOHNDOE83]

Stock rev box is OK, I use a white brothers cdi and after my testing of several different brands the white bros is by far the best and worth the price.

I would like to try the programmable cdi's though.