ok smarty solve this riddle

[johnafun]

04 ltz 400 engine mod's jeted,air lid off,hmf, rev box

every so often some water would get into the air box causing the bike to bog at high rpm's.no big deal drain it and go.so we thought.
same problem later devoloped but no water found no where getting to fuel. but then would misteriously clear up.

finally did it one last time at track. found water and mud in spark plug retainer. pulled plug , flushed the crap and turned over engine to try and spit as much out. nowturns over but wont start or fire.but yet pull the plug and ground it and got spark.put new plug in still nothing.

took it to mechanic he is baffled. got spark good compression,good fuel.now they are suspecting a valve.still no word back on that yet

so all you master mechanics try and solve this puzzle .whats your thoughts?

[johnafun]

ooops thats an 06

[F-16Guy]

I'm guessing a tight intake valve.

[wilkin250r]

Valve problems generally create poor compression. If it truly does have good compression, then it doesn't sound like a valve issue.

[johnafun]

update:

i had them humer me by trying the stock cdi box. when they disonected the cdi box the plug was filled with dry mud. so with the stock box it on it sudenly was fireing and trying to start. but back fireing and not staying running. so now theyr suspecting like yall are saying.

theiry is cdi box shorting out causing stress on valves . valve conditions unkown yet but were sure were on the rite path

will update later

[bwamos]

I am assuming you have already completely drained the fuel tank and carb and used new fuel.

How do they think the CDI box is stressing the valves exactly?

My theory is they are making stuff up as they go, lol. :)

Have they checked valve/cam timing? (sounds to me like you may be off a tooth or two) Often compression looks close to the same because the exhuast gasses aren't clearing out completely either.

What color was the spark?
Have they checked the spark timing?

Not sure if the z400 has a flywheel key like the 400ex, but if it failed, everything would "look fine" except it would be sparking at the wrong time.

If your CDI was bad you wouldn't be getting a good spark. Your CDI controls your spark.

Have you checked to make sure all of the carb vent lines are unobstructed?

Just throwing some random stuff out there.

[wilkin250r]

Originally posted by bwamos
IMy theory is they are making stuff up as they go, lol. :)

I'm with you. How exactly is the CDI going to stress the valves?!?

[johnafun]

im no master mechanic myself but i got alot of bad experience behind me LMAO ..it makes some possible sence. if the cdi box was causing the engine to run like crap past a certain RPM like it was(of course we know the purpose of a cdi box and this model after market cdi box ive read up haveing alot of probs). maby i missed mentioning that idle and reving till mid range was good till it finally wouldnt fire at all. like i said it felt like it had water in fuel. but found no water. even draining the tank into a bucket where we could look for water. anyway back on track so an engine running like that is highly possible to through a valve or jump timing. hmmm yes yes you agree? especially after replacing the cdi box and sudenly its fireing again. now me myself and im sure theyve thought of it to, is that your guyses thiery is totaly true .whats not to say it through a valve or the origenal problem was bad valves ,timing or bad ring. at this point we may never truely know what was the origenal problem.but we do know at least the cdi box was bad. they are continuing on going into the engine to check all the stuff you guys mentioned.

im like the worst customer you could have calling all the time."so hows it going ? what ya got? where we at? i hate tairing into an engine. ilde rather pay someone else to do it.cuz honesty im impatient and im really not that good at trouble shooting internally unless its obvious. but this is a good lesson for me im allready learning somthing new.luckily these guys know my wife and she told them dont let john bother you ,hes just not used to someone else working on his bike's with out him being there or doing it himself.

high performance minded mechanics are hard to find in my neck of the woods unless you drive 3 hours

i really apriciate yalls input

[dpizz450]

my kfx was doing about the same thing. check ur carb and clean it out real good. intake and air box also clean good. if that doesnt work i would guess its gonna be the timing chain or the valves. when mine was doin that i had to clean my carb and redo the shim on my valves. now it has ran perfect ever since. im not very mechanically inclined, but almost positive its gonna be one of those. id clean the carb then go after the valves. the valve shims are onlylike 30 bucks. cheap quick fix. good luck and let us kno what u find.

[pro-rider46]

Originally posted by YZrida
. the valve shims are onlylike 30 bucks. cheap quick fix.

are you talking about buying shims individually? because if i was him i would just buy the hotcams shim kit off of ebay for 65 bucks and then your set for as long as the quad is running

[F-16Guy]

You don't need to buy a kit. You can remove the cam, take the existing shims out from under the tappet "buckets", temporarily reinstall everything, and then measure the gap between the cam and buckets and figure out exactly what shims you need. You just need to subtract the specified valve clearance from the total gap measurement, and that will give you the thickness of the shim you need. You'll have to do the exact same procedure with the "kit", but you won't end up with 50 shims you'll never use. Kits (jets, shims, whatever) are a great way to get you to spend money and that's about it.

Before I went through all of that trouble, though, I'd take the carb apart and clean it well.

[johnafun]

ah yes many inputs . the carb is clean was recently rejeted and fitted with a K&N filter. so valves pop up again and again. im trying not to do any more mods to it.it's a great handling quad as it sits.luckily i still have my 07 LTR450 to keep me ocupied.but i still love my 400 better. whieght to HP ratio is perfect. the ltr though has much more horses but i can run better times on the 400 cuz the ltr constently spins and slides loosing traction and time

[graff2000]

just throwing this out there but if your running stock valves with a rev box i have seen some valves stretch and make a no start situation.

[johnafun]

anything is possible at this point im sure.

update:

the origenal shop i took it to has given up and i broke down and sent it off to a certified dealer who's mechanics deal with mostly sport 4wheelers. a long drive but at this point gotta do it. there in the middle of tairing it down and suspect the cam chain tensioner broke or loose. so far. just a guess at this point by them.will update later

[wilkin250r]

Originally posted by graff2000
just throwing this out there but if your running stock valves with a rev box i have seen some valves stretch and make a no start situation.

But if the valves have stretched, he wouldn't get any compression. The first post says it has good compression. If that's true, you can rule out valve stretch.

[johnafun]

yuppers the first thing the new shop did rite off the bat was they turnes it over ,backfierd,got ome meter checked spark strength.good there .then pulled plug and used compression gauge. compression matches up to specs.then to valve clearence. its on spec. by then it was 5 time to nock off for the weekend and im sure they were sick of me standing over theyre shoulder.lmao. i wish i could be there monday for "the rest of the story"

[wilkin250r]

Good compression, strong spark, valve lash within spec. Okay.

My guess is camshaft timing off (like you said, maybe cam tensioner?)

Or the ignition timing is off, and the only way that would happen is a sheared flywheel key.

That's my official diagnosis from a thousand miles away. Keep us updated on the actual results, though.

[johnafun]

ATTN: WE HAVE RESULTS!!!!!!!!!!!!!!!!!


ok at first they thought they hed good compression . someone later used the same compression gauge and found it was stuck.so a new gauge was used and found low compression.

1st...the piston rings where found to be froze into the piston caused by (if you read the first post) mud that had fallen into the head after removing the spark plug. cylender walls are ok.

2nd... the original problem was the after market CDI not working properly emiting crazy eregular spark patterns and strength.sometime working good sometime's working bad. after inspecting the cdi box. there was no inspection approvel stamp. the cdi box was baught off ebay suspecting that wholesaler baught rejected parts and selling on ebay.

so new piston and rings and new CDI box.

the lesson: be carfull what you buy on ebay and if your spark plug recess is full of mud and water dont pull the plug LOL

thanks guys have a good one

[wilkin250r]

Lesson #2: Make sure your tools are correct and accurate.

[John451]

My friend had the same sort of problem but it was because he had a paper towel in the carb??? I have no idea how it got there i think he put it there to get water out But he completely denies it. LOL. But that's good that you got it sorted out. Good luck!