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  #1  
Old 08-28-2012, 10:39 AM
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Default Just got an 02' 400EX, and have some problems

     

Hey everyone! Yesterday, I traded my trail bike, an 04' KX250, which was getting a little worn out, and needed plastic, for a 2002 400EX even. The guy who owned the 400EX took pretty good care of it, at least what I could see. He showed me a receipt for almost $1500 that he had done at the beginning of the summer.. he apparently burned up the motor and had this work done... on the receipt I can see:
Cylinder boring with new piston and rings (I wish I knew how oversize they went)
Stage 1 hotcam
New valves and basically top end...
and it as a White Bros. E Series slip on (I've never had a "tunable" pipe like this, I know nothing about them!)
I took it for a ride yesterday, and found a problem... on a long, uphill straight I have, the bike would cut out at WOT... then you back off the throttle and it picks right back up... slam the throttle wide open again, and it starts to rev, then dies... is it starving for fuel???
I took it home and started taking off the plastics for cleaning. I got to the air filter.. It had a brand new UNI filter on it, which was dry as a bone (no wonder he burned up the motor!) I took it off and washed and re oiled it. I put it all back together this morning, and am going to test it again this evening.
Should I put in a bigger main jet? This is my first 4 stroke quad, I've had many many 2 strokers, so this carb is definitely funny looking to me!
Is there anything I should know, or any tips you guys could give me for this bike??
Thanks a million for any and all help!
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Old 08-28-2012, 12:14 PM
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Default Maybe

It may be as simple as thge float being set too low and running out of fuel on the top end due to lack of fuel in the carb. It couls also be a partially clogged fuel screen in the per cock or a partially clogged carb vet line or apartially clogget fuel tank vent line.
By oiling the air filter you have already richened the fuel air mixture, so no bigger jet should be needed if correctly jetted in the first place.
One other place to look is at the spark plug wire and the spark plug boot. If the resistance in that area is too great it will also cut out at high rpm.

Paw Paw
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Old 08-30-2012, 05:54 AM
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Thanks for the reply, PawPaw!
I contacted the previous owner last night and asked him if it used to do this before the rebuild, or after...
He told me this: "It's already got a stage 2 jet kit installed, the guys at the shop who did the rebuild told me that the jets are bigger than stock, and it will run best with the spark arrestor out and airbox lid removed"..
Now, to me, I don't know what to think.. He doesn't know which stage 2 kit it has, FMF, WB, JD, etc.... and also Ifound out that the displacement has been upped to 407cc due to the boring, if I did my math right lol.
It has a WB E series pipe, with the discs on it (11 are on it, don't have any more), with the spark arrestor (the solid disc on the back??)... should I remove the spark arrestor? I do not need it where I ride, however I DO NOT like excessively loud 4 strokes, but I will run it this way if I need to...
I ruled out the floats because I can make it cut out like this cruising around the yard in 2nd gear... putting around, assuring the bowl is full, then lay into it... cuts out.
It also has some nasty backfiring.. Not the normal blubbering/low pop/blubber that my WR250F makes on decelleration (ACV bypass has been done), but a LOUD POP..... POP, almost as loud as a gunshot! This quad DOES still have it's ACV, so it shouldn't backfire at all, correct?? This evening I am going to try to remove the carb and give it a thorough cleaning, however I am nervous about it... This carb looks nothing like anything I've ever messed with!
The only 4 stroke carb that I've worked on, and know inside and out, is the Keihin FCR on my 05' WR250F... this thing on the EX looks a lot different. Is there anything I should know before I tear into it?
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Old 08-30-2012, 07:03 AM
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Is the timing off?
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Old 08-30-2012, 07:08 AM
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Default OK

OK, you could still be having a float issue. The fuel flow could sufficent at slower rpm, but when they increase or the fuel draw is increased greatly it could be running out of fuel until the draw is reduced.
The unit has has a lot of stuff dune to it and thus it increases the amount of possible issues created.
The jetting kit's are not always correct and thus could be lean. The popping you wrote about also indicates it's lean and or has a blown exhaust gasket.
Understand that lean can also be from air leaks at carb boots or from fuel starvation due to lack of fuel flow. Reduced fuel flow can be caused by a bad fuel tank vent, clogged fuel bowl vents, dirty fuel screens or improperly set float.
Also excess exhaust back pressure can cause issues at upper rpm ranges that would mimic fuel starvation.

Do you have a service manual for your unit? If not , get one asap.

Paw Paw
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Old 08-30-2012, 07:27 AM
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Thank again!
yes, I have a manual, the Honda owners manual, which actually has a lot of information in it.

Can someone tell me a little bit about the slip on pipe? The WB E Series? Will removing some of the discs cause the pipe the be quieter, and affect my jetting? Richer or leaner? What about adding discs and/or removing the spark arrestor.. I've never owned an exhaust like this, so it's all new to me. I also cannot find a manual for this exhaust, since WB is out of business...
You were saying that a restrictive exhaust can mimick fuel starvation??
Oh, and at low RPM's when I tromp it wide open to cause it to cut out - the engine hasn't built up enough RPM's to suck a lot of fuel yet, this is why I thought that perhaps the main jet is the problem rather than floats... I will check my float level anyways to be sure.
Is the carb hard to remove/service on these?
Also, I'm pretty sure the engine is on time, since it has great response in low to midrange, starts very well, and has a great pull off idle.
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Old 08-30-2012, 07:51 AM
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Default OK

Ok, you need a "service manual".....
The service manual will cover the carb, float height, timing and many other issues.
Just stating that everything is ok without checking is not going to get your issues fixed.
The cut out when you "romp on it" is most likely a lean condition. It can be caused by too low a float setting or your accelorator pump is not giving it enough fuel at the proper time and thus it becomes lean with the sudden induction of air. The fuel screw setting under the carb can be adjusted to help with the initial lean issues when you "romp on it"
Here is a breakdown for your carb.
http://www.bikebandit.com/houseofmot...14554#sch96829
Here is a link for a service manual.
http://www.ebay.com/itm/1999-2007-Ho...b2be84&vxp=mtr
Paw Paw

Last edited by PawPaw; 08-30-2012 at 08:00 AM.
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Old 08-31-2012, 09:58 AM
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Ah thanx for the info and links!
Last night I pulled off the plastic, removed the airbox, gas tank, and the carb. I was disgusted at how grimy and dirty the airbox and carb were... They've been disassembled and are soaking right now in cleaner.
I just got off work, so I'm going to finish cleaning everything, reassemble it, then see what happens. Perhaps a clogged jet or passage is causing the fuel starvation (if my floats are at the correct level). Then, if the problem still persists, at least I'll know everythings clean, and it's not a problem with gunk.
My manual is 240 or so pages, and it does go over valve adjustments, float level, ect, however I'm sure it's nowhere NEAR in depth as a Clymer manual.. I will save up for one.
Thanks for all the help thus far!

BTW: Anyone know any details on how my exhaust system works? (White Brothers E-series) I have 12 discs on right now with the solid spark arrestor... If I remove some discs and run, lets say, 8 of them perhaps - will that mean my exhaust will be quieter and a bit more restricted?
If I remove the spark arrestor, the exhaust will go straight through, and the discs will have no affect, correct? Or will the discs still affect performance even with the sparky removed?
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Old 09-04-2012, 10:05 AM
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Alright, update! I don't have internet access available at home, so it's taken me all weekend till' I was back on campus to use the computers..
After removing the carb and airbox, I was amazed at how filthy the thing was! On the airbox side of the carb, at the top of the mouth, there are 2 holes... On my other bike's carb, these are the Pilot Air Jet and Main Air Jet. These passages were filthy, and the wider, oblong one was completely plugged with black gunk! Completely, I am not exaggerating. I took the carb completely apart, and blew out everything with carb cleaner, followed by compressed air, then again with carb cleaner. The floats are working correctly, although there is a burr on my float valve, so that will need to be replaced. I noticed that my pilot jet was stock, a #38, and my main jet was weird... It was like a regular main jet, but longer, and with another jet attached to the end of the main body?? Perhaps a JD jet or Dynojet? It was a #170. I completely cleaned and reassembled everything, and got the bike back together.
Success! The clogged ports were definitely a big part of the problem, because now, I get no hesitation or cutting out on WOT. I still get some annoying backfiring, but I believe my air cut off valve is fault. I removed it, and tried to clean it, but I couldn't blow air through any of the passages.. Since it isn't working, I'm getting really lean on decelleration, and getting some loud backfires. It only backfires if I am decelling from around 4500+ rpms... it doesn't do it when I'm just putting around. My air screw is over 3 turns out, and still sounds lean when I'm riding, and doesn't have the low rpm power I feel it should have with the Stage 1 hotcam and exhaust, so I'm going to install a #42 - 45 PJ soon as I can.
Again, I thank you all for all your help!
Also, what exhaust is everyone currently recommending for the 400EX, I am looking for a moderate to low exhaust noise, and I prefer torque and low end pull rather than high RPM power. This WB E-series is just too loud even with the spark arrestor installed, and it doesn't feel like it's giving me any more power than a stocker would.
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