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Odd issue with ZX6R F series 1997

269 Views 11 Replies 8 Participants Last post by  Clive
2
Hello everyone,

Recently upgraded from ex500 to ZX6R, I took an old lady with carbs because 'I prefer old bikes' and 'its all mechanical it's easier' (馃槀馃槀)

Turns out I am unable to figure this one out.. can someone help me? 馃槵

Here we go:
Idles normally.
I can readline the bike in neutral and I do not have any weird behaviour.
I can readline the bike in 1st gear OK and in 2st gear with a slight moment of hesitation at 5k rpm and will reach 7k and goes to the red line perfect.
Then I can pass 5 6 7 k at third gear albeit with a lot of misfires and cutoffs and then off I go to red line.
On fourth gear and above I can't pass 5k it will misfire too much and throw me forward and backwards.
Last thing: when I go to red line say in third gear but decelerate (whilst leaving the throttle 20% open) (staying in 3rd gear) and enter the zone 7-6-5-4k it seems to accentuate the issue the engine start to burble, bog down, sort of misfire or was starving for fuel.

Things I've done:
I've cleaned the carbs
New sparks
New ignition coils.

Things I have not done:
Compression
Valve clearance
Check the rest of electrical system

Because of the weirdness at 5k my suspicions went to the transition from pilot jet to needle jet and the diaphragms. I've checked again and again if not pinched or whatever but everything is installed ok...

Can someone help I'm getting mental on this I can't figure it out...

Thank you!!!!

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Jetting/filter/airbox all OEM? If so, then "could be" a weak spark, if load causes it to stumble.
Jetting is all OEM. Airbox is OEM as well but exhaust and pipes are not full line akrapovic. Could this cause the issue ?
Open exhaust causes leanness. Do a plug chop and you will be able to see if this is the case.
Beautiful bike!!

i just fought through weird misfire issues on my EX. Scratched my head for quite a while trying to tune what I had, but eventually my fix came in the form of a new replacement CDI box. Sounds like your fuel circuits have been gone through pretty well鈥 new coils and plugs Rules those out.

the 鈥渢hrowing me back and forwards鈥 thing makes me think of losing spark quickly, on and off, an electrical gremlin. My $$ would be on the CDI.
Revving it at idle (no load)... all good. Powering it under load - weird problems as described and "starved of fuel" - or running lean? My guess is an air leak on the intake side. Seen it before on a big Suzie... ran fine up to 5 or 6 thou, then died a slow death. Coast to a stop, start her up, all fine! So, carefully inspect the intake side first. And I mean very carefully. Look for small splits or cracks, use a high powered torch if you have to, any small cracks will open up when under load, as vast amounts of air are sucked through. After that, I agree with the above, could be an electrical loading problem, again, seen it. All fine iding etc, soon as the engine demands current, all sort of weird fluctuations begin! Anyway, start with the easy stuff, let us know how you get on...
I'm with Gedde, and his thoughts about a possible issue when transitioning from different jet circuits. The bike runs fine after 7K, so I don't think it's CDI.
@Gedde please post total mileage/km's on subject bike
reminds me of a ZX7, looks like an ex track bike to me. When you had the carbs off, did you blow air through the inlets and watch the slides go up and down? Just a thought. Let us know how you make out.
Hello everyone,

So... it was a airbox issue with air leak because a vacuum valve was not set up correctly.

Basically on this bike there is a pipe running from the carbs to the top of the airbox. This pipe helps the bowls to get 'pressure' from the airbox running as the vaccum created in he throat of the carb is not enough to get all the fuel out. I do not recall a deisgn this way on the EX where the air box is plugged to nothing besides the crank case vent... apparently it is a ram air design so different from the EX with this additional pipe.

So plugged it in and it all worked.

Then ran the bike and had issues at 9K rpm exactly, turned out that the air filter had way too much oil on it caused trouble.

Also figured out that the main jets on cylinder 2 and 3 are bigger that those on cylinder 1 and 4!!!!!!!!!!! As opposed to the EX where you dont have to pay attention to this detail.

So bottom line these things are extremely sensitive lol, it was a nightmare to figure out but now all good! Thank you.
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glad you got it sorted, the solution for one bike isn't always the solution for another one. which makes diagnosis sometimes difficult. and just to think some think the EX is complicated.
Hello everyone,

So... it was a airbox issue with air leak because a vacuum valve was not set up correctly.

Basically on this bike there is a pipe running from the carbs to the top of the airbox. This pipe helps the bowls to get 'pressure' from the airbox running as the vaccum created in he throat of the carb is not enough to get all the fuel out. I do not recall a deisgn this way on the EX where the air box is plugged to nothing besides the crank case vent... apparently it is a ram air design so different from the EX with this additional pipe.

So plugged it in and it all worked.

Then ran the bike and had issues at 9K rpm exactly, turned out that the air filter had way too much oil on it caused trouble.

Also figured out that the main jets on cylinder 2 and 3 are bigger that those on cylinder 1 and 4!!!!!!!!!!! As opposed to the EX where you dont have to pay attention to this detail.

So bottom line these things are extremely sensitive lol, it was a nightmare to figure out but now all good! Thank you.
RAM air is a pain when setting up the carbs, but yes, seems we were heading in the right direction with this one. Just to remind you, the main jets on 2 and 3 are supposed to be slightly bigger, due to these cylinders running hotter. If the jets were the same as 1 and 4 then 2 and 3 would run lean, hence the difference.
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