Weird behaviour

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Joined: Fri Jul 16, 2021 9:06 am
My Bike: ZXR400 L7

Weird behaviour

Post by Raishin_27 »

Hi guys,
I am having a carburation problem on my bike which is driving me mad sorting it out.
Quick recap:
L Model 1997
Fully stock, no engine modifications.

Problem begun recently after not being able to ride it for health reasons.

I had bike since many years and never had so much problem getting it started when cold... Now is always difficult.
Sometimes if you open throttle 1/4 or 2/4 and try to start it quickly start without issues. If you try with no throttle, less than 1/4 or with a bit of choke it takes time to start and the engine start "slowly" at super low rpm like it was dying.. an slowly rpm goes up till idle.
If you use full choke, impossible to start.
If after starting you try pulling the choke in the past it used to increase revs till warm now dies.
When you ride it.. it goes not so bad. BUT if you make her scream for a while riding fast..when you slow down for a while it runa rough at low rpm..

Things already did:
Cheched carb boot leaks
Replaced sparkplugs
Fully rebuilt carbs with new oem jets and settings, new seals, new float rubber needles, cleaned carb bodies and so on.
My mains are 95 which are stock for Italy where I live, my mixture screws are now 1/4 turns less (leaner) than stock and seems to be a bit better.
I checked float levels..they were almost 14mm so very out.. I then procedeed to set them at 11 like manual say and it was a disaster.. so rich almost unrideable. Set them back at 13mm and back as it was before.
Airfilter new, oiled as supposed
Airbox seal new
Chechek compression, 2 full healthy, 2 bit less but still inside tolerances.
Oh, forgot.. if I start it when hot it starts flawlessi just touching start button

Lately i did a couple of mods.. I have the mod about fuel pump like some do on racebikes to have it run when you turn the key.
Replaced old coils with cbr600.
This 2 mods improved a lot startup and idle running.

Does anyone have ideas? Something lead to think is very rich.. something lead to think it may be lean.. itd driving me mad...

(Sorry if my english is not perfect.. I am Italian)
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