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ZXR 750 L (1994)

12K views 80 replies 5 participants last post by  Pyke13  
Hi all,
I still own my baby and after a long time I decided to work on the carb tuning.

Here's what I did so far:
  • removed the Kleen stuff (putting a pipe instead of the two plates)
  • installed a full exhaust system made by shark in the 90s (it's for the K model but it does fit pretty well)
  • installed a Factory Pro Ti needle but not the main jets: I preferred an original Keihin 150-160-160-150 setup as advised by many sources
  • installed a +4 deg. advance kit
  • installed a BMC airfilter
  • airbox screen removed and sealed all the holes except the one close to the carbs (bottom), where I'm picking up air for the carb vent pipe (float bowl vent mod)
  • spark plug with double electrode (CR9EK)

and:


Now the bike is really screaming from 3000 to 8000RPMs at WOT, no flat spots and the power is delivered very consistently.
Sometimes she idles a bit higher and after a while getting lower, so not always stable.
And here is the issue: @ WOT after 9000-10000RPMs she has an hesitation and runs irregularly. Not reaching the redline smoothly and I did not insist (it seems leaning out but not totally sure)

I've read a lot on many different sites and I am totally confused.

Before reaching out a shop for a dyno run and checking the AFR, I'd like to have you opinion on that.

I'd like to understand what the float height does and if it might have an impact here (is it leaning out when the RAM effect is building up?) I read somewhere that it should affect only idling and low-midrange but I'm not sure.

float bowl vent mod: I plugged the carb vent pipe to the lower nipple of the airbox (the rubber one that has a 90° bent). Should I use take the air pressure from any other nipple of the airbox (i.e. the original hole on the right hand side where the pipe slides in with no gasket at all?) I thought it might not be enough pressurized given the location of this nipple... who knows.

previously I was running a 160-170-170-160 main jet config and the spark plugs were (not soaked) but quite black (see the picture; I also scratched the exhaust can with the paper to check the colour). that is why I wanted to go down with the size to the current setup. I am quite surprised that the FP kit goes with a big size main jet kit (around 180) that sounds too rich like the stock 170-190-190-170 config.

I'd really appreciate if anyone can post a picture of the modded airbox for a 93-95 ZX7R (or ZXR as known in EU).

thanks all for any advice!
View attachment 21851
Adjust your fuel mixture screws to 2 half turns out and test the idle at operating temp.
Do you have another air filter to try? I know the BMC filters are pretty porous and allow for more flow.
 
ok. I guess the change to the mixture screws should affect the idling right?

Re. the air filter, this is the street version which is in line with K&N. The BMC Race filter was too much for a street use...
Anyway I can probably get a stock one if you think it's worth trying.
thanks
Well, your top end fueling is too much (probably. by looks of your spark plug). I was thinking you either need the race filter, a fatter needle or a smaller main jet.
 
ok that is exactly what I thought that led me to lower the main jets from 160-170-170-160 to 150-160-160-150.

so the issue at high revv must be something else then the jets....

in the meantime I found this in the 92 race manual.
View attachment 21852
I'm an idiot. Did you change the main air jets or the main fuel jets?
 
ok so I started the work and here's how's today
View attachment 21878


so disconnecting these pipes and I'll hook these two up together (after removing the epoxy seal I did)
View attachment 21879


btw in the meantime this is how the spark plug looks like after re-jetting.
View attachment 21880
it seems a little bit on the lean side, probably due to the wrong float bowl mod I did.
I will keep this setup and re-test when the new vents line will be installed.

apologies for the big pictures, I should have resized before posting.

Cheers
I enjoy big pictures
 
so... here I am again after a bit of work.


New vent pipe prepared:
View attachment 21923

This is how I prepared the airbox (I used a plastic 90° irrigation elbow :))
View attachment 21924

Then I hooked up the two parts together:
View attachment 21925

This looks pretty much "acceptable" for my (very low) standards.
All the other holes have been sealed...


This weekend I'm going to re-test the bike, hoping the issue is solved.

Unfortunately while doing my searches on the internet I found this... which drives me mad... I really hope this is not my case....

Bike not reaching the redline | Andys Kawasaki ZXr/ZX7R Tribute Website (andys-kawasaki-zxr-zx7r-tribute-site.net)

:rolleyes::rolleyes::rolleyes::rolleyes::rolleyes:
ok, just to provide a feedback... I just went to test the bike and now she is reaching redline easily and without any hesitation. the vent line change indeed resolved the issue. Thanks guys for the help!

Next step will be to go through a dyno run and checking the Air-Fuel ratio.
I will post the outcome here just to provide some facts.
This will happen later this year, probably after my summer holidays. :cool:
See! No broken inner valve spring here :)
 
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Reactions: maxlion75
This is coming along nicely