z400 cuts out over whoops

[Chevy1500z71]

for most of the time iv owned my bike, probably for the last few years, my bike has always cut out over the whoops. what happens is im cruising along 4th or 5th gear with he throttle pinned, and it runs great, hit the whoops and lean back and as the bike is jolted around over the whoops it looses power, it cuts in and out(no backfires or anything to crazy tho) its as if it starves for fuel, or possibly a loose wire jiggling around. iv been meaning to make some room in the garage to get a chance to look at the bike but it would be hard to trouble shoot it since i cant really test if i fixed the problem with the small test track behind the garage, no whoops, so i was hoping that you guys may have some experience with this, maybe its common?

right now what im thinking is i need to set the float level on the carb, possibly the carbs bowl just doesn't hold enough juice, iv never heard anything good about this series of mikunis. or possibly the wire where i spliced in my tether kill switch is loose. possibly the ecm is just going bad, when i turn the key off sometimes the bike may run for several seconds before it actually dies, this occurs mainly when the bike has been ridden really hard and its running hot. just what i can think of right now, maybe you guys can narrow it down and save me some time. iv never really spent much time on this bike really, regular maintenance is the extent of how much i work on this bike, iv kind of let it go out of lazyness, to much work to do on the truck, no time for the atv, iv ridden it like this for years.

[yfz122]

If it were mine I would start at the float level.

[Chevy1500z71]

If it were mine I would start at the float level.

yea that's pretty much what i planed on. i was hoping this was a common problem that someone would have an easy answer for... guess not.

[z400250]

does it do it on flat ground in 5th pinned for a bit? what about in slower speeds on the whoops?

[Chevy1500z71]

does it do it on flat ground in 5th pinned for a bit? what about in slower speeds on the whoops?

no, never on flat ground, slower speed whoops its normally good to, jumps, also good. its just the really chopy whoops and really igh speeds, the bike has to be jolted around pretty hard for it to occur, unfortunately it happens very often the way i ride. other then the high speed whoops it runs perfect. iv got a bad feeling its an electrical issue but i just put the bike up on the jack and im ready to pull the carb, lets hope its the float level.

im trying to get this thing ready for croom in a few weeks, gota service the filter, chain, oil change, ect. and id liek to get it running good while im at it.

[Baileygunns]

Take a piece of clear tube and attach it to the drain on the bottom of the bowl. Hold the other end of the tube over/higher than the carb. With the fuel on, bike not running, open the drain on the bowl and see how high the fuel goes up the tube. The fuel in the tube will be the same level and the fuel in the bowl. This will show you where the bowls are set without taking the carb off... Quick and easy.

I know on my Raptor the fuel level should be about 1mm/2mm above the bowl gasket.

I got some tubing from the auto parts store for about a buck. Take your drain line off the bottom of the bowl with you to match it up.

[Chevy1500z71]

Take a piece of clear tube and attach it to the drain on the bottom of the bowl. Hold the other end of the tube over/higher than the carb. With the fuel on, bike not running, open the drain on the bowl and see how high the fuel goes up the tube. The fuel in the tube will be the same level and the fuel in the bowl. This will show you where the bowls are set without taking the carb off... Quick and easy.

I know on my Raptor the fuel level should be about 1mm/2mm above the bowl gasket.

I got some tubing from the auto parts store for about a buck. Take your drain line off the bottom of the bowl with you to match it up.

iv never done float level by measurement to be honest, i just hold the carb on its side and make sure the float is level.

youv got a great idea tho, itl definitely give me a ballpark idea if my float level is way off. thats a trick ill remember.



i think the problem is electrical tho, i had a pos pro design tether kill switch onm there that barely worked, that could ahve been the problem so i removed it. the key switch is next, its got alot of corrosion on the wires i think, hell the headlight wires pulled free from it long ago, i ended up putting the headlights on a  toggle switch.

[trx#9]

Drop the main jet 1 size and see if that helps, sounds like your a tad bit rich.

[Chevy1500z71]

Drop the main jet 1 size and see if that helps, sounds like your a tad bit rich.

i doubt yoshis jetting specs are wrong, i also doubt 1 size smaller will change the way it runs at all. ill try it if all else fails

[01ZX12R]

You will be very suprised at what 1 jet size will do..

[Baileygunns]

It's actually an exact may to figure out where your fuel level is... The floats being "level" to the earth isn't necessarily the same as "level" or amount of fuel in your bowls....

These pictures ore of a Raptor but it's the same for all carbs.





finger is not pointing at the fuel level, it is only holding the pipe in place.




Maybe this will come in handy for someone else reading this too...

[Chevy1500z71]

i took it out for a test run yesterday and it did the same thing. it seemed like it got worse as the day got on, as the motor got hotter. towards the end of the day i poped the fuse under the seat, this happened soon after i turned my headlights on which are wired to make the highs and lows come on at the same time, iv got the high beams wired like this on my truck for the extra lighting offroad and it works well, maybe its to much for the z400s electrical system to be powering both the highs and the lows, or maybe this problem is related to my other problem, the bike running bad over the whoops. who knows.


so next line of business is to get rid of the key, if that doesn't do it, drop the main jet a size and see if i possibly just have a rich condition. a guy on the z400 forum told me that he had the same problem when his choke cable was holding the choke out a little bit, thats a rich condition, i know my choke is fine, but i could still have too much main jet... if that doesn't do it then maybe the ecm/revbox or whatever the hell its called on an atv is going bad.

i was also thinking that maybe this is ok, i mean, it runs good otherwise, maybe i just ride it to hard. i wouldn't really expect a carbureted motor to do well beings bounced around so hard. another thought, maybe i rev the piss out of it too much, maybe im just hitting the rev limiter, maybe im so close to the limiter that once my back tires leave the ground for a moment it abruptly hits the limiter.i nail the chopiest of whoops with the bike winding out at the very top of 5th gear, i really let the motor scream... i just don't know what to think of it tho, i could swear i used to be able to do this with this bike, its been so long tho. like i said, iv had this issue for years.

and for my last though, the petcock, its one of those stupid vacuum controlled ones. although i switch it to the free flow position just to rule it out, maybe that not enough, what if there's more to it then that. iv never really though about it before, iv seen them go bad a million times but its normally just as simple as they puke fuel out of the vacuum line, i replace the whole petcock, problem solved.

[svtbolt04]

There is a vent hole on the side of the cylinder, my old z400 got it clogged one time and I had no idea what was going on, then a guy who raced them told me to blow it out. Worked fine after that.

Its on the right side.

[Chevy1500z71]

There is a vent hole on the side of the cylinder, my old z400 got it clogged one time and I had no idea what was going on, then a guy who raced them told me to blow it out. Worked fine after that.

Its on the right side.

Compression release? ill take a look. thanks fred.


EDIT: you must be talking about the vent on the cylinder that goes to that emissions box thing. ill probably completely remove the whole emissions control deal.

[svtbolt04]

Im guessing it is the compression release. It is kind of raised up and what not.. Just blow it out with an air chuck, but I wouldnt aim it right at it with it blowing 100%.

It may not be it.. but its worth a try.

[Chevy1500z71]

Im guessing it is the compression release. It is kind of raised up and what not.. Just blow it out with an air chuck, but I wouldnt aim it right at it with it blowing 100%.

It may not be it.. but its worth a try.

ok, im thinking of the wrong thing, im looking at a crankcase vent. ill take a look.

hey you wouldnt happen to have a manual for the z400 would ya? while iv got the bike somewhat apart i went ahead and checked the valve lash since iv noticed a little valve train noise. my intake is .004 and my exhaust is .006. cam chain tensioner is almost all the way out, probably could use a cam chain, wondering iv the valve lash is out of spec.

[svtbolt04]

I dont have the manual in paper form, but I am in suzuki right now and all of their manuals are online. What do you need? Specs?

[Chevy1500z71]

I dont have the manual in paper form, but I am in suzuki right now and all of their manuals are online. What do you need? Specs?

yea, just the valve lash specs would be fine. thanks.

[svtbolt04]

Valve clearance

IN: 0.10~0.20mm (0.0039~0.0079 in)
EX: 0.20~0.30mm (0.0079~0.0118 in)

Make sure its on TDCC and the engine is cold. Suzuki actually prefers you to set the clearance right in the middle. So, .15 for intake, .25 for exhaust.

I actually have a complete troubleshoot for the engine running poorly at highspeed.

[Mars]

There is a vent hole on the side of the cylinder, my old z400 got it clogged one time and I had no idea what was going on, then a guy who raced them told me to blow it out. Worked fine after that.

Its on the right side.

Compression release? ill take a look. thanks fred.


EDIT: you must be talking about the vent on the cylinder that goes to that emissions box thing. ill probably completely remove the whole emissions control deal.

I think your looking at the vent for water to drain out of spark plug hole/valley.

[Chevy1500z71]

mars called it, its just the drain for the spark plug hole. maybe if it gets cloged up it causes crap to interfere with the spark plugs connection with the plug cap, that wasn't the case with me tho.

[erbilabuc]

Ive got this same problem and it happens when Im coming up on a jump or riding uphill on a dune. I think it may be the CDI because of the fact that when I put the key to "off" it still runs for like 3 seconds and then it shuts off.

[stevemiller21]

I sent a message to you about this as well, but just in case somebody else is having this problem, I would like to share my experience with this problem.  The vacuum slide on the carb is the problem if it is a stock carb.  When you go over a whoop the slide moves causing your bike to cut out.  I fixed the problem by installing a FCR carb. 

Also, another person said their bike was still running after the key was turned off.  It is a common problem due to the fan running when you shut the bike off. 

Another problem you may encounter with a z400 is the reverse rev limit switch down by the shifter will make one cut out as well.  I cut my wires and bypassed the switch to fix that problem.

I have had a z400 since 2003 and have encountered most problems associated with it.  Hope this info is useful and if you have any more problems feel free to send me a message!
Steve

[Chevy1500z71]

took the bike up to croom this past weekend and it ran good. it did it a little bit, it is definitely the carb. the float got stuck at one point and the problem was exactly the same except it didnt mater if i was hitting the whoops or not, drained it and smacked the bowl till it freed up and it ran great all day. the fact is these cv series mikunis are just crappy carbs. it still does it slightly, i just ride it too fast over the whoops. changed the oil, new plug, went through the carb and the bike overall runs great. id change the carb on it but im trying to sell it and get into a 250r.

thanks for all the help guys, im going to blame it on the carb for sure.