Bike running fine cold and very bad when warm

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Posts: 6
Joined: Fri Jul 16, 2021 9:06 am
My Bike: ZXR400 L7

Bike running fine cold and very bad when warm

Post by Raishin_27 »

Hello guys.. hope there is still someone reading here..
I am kinda desperate with my bike.
The bike sat in the garage for a couple years because of my health conditions.
I then took her out and was running veru rough.
So I went for a full carb clean, new plugs and so on.
Found float levels all messed up(never touched them before) and put into manual specs so perfect at 11mm.
Begun to run kinda ok.. but very difficult to start (before the forced stop she used to roar to life in a button click, after that seems to slooowly coming to life).
The majn problem is.. when cold the bike runs fine.. very very smooth. After warmjng ease a bit more on the throttle (staying at city rpm so 5..6000.. ) and the bike feels bogging like mad. Sounds like a twin and has problems taking more revs.
It feels like when 2 of my idle jets were clogged after winter stop.. the bike was rough, sounded like a twin and low power, but this time they are clean..
Maybe something stuck in carb passages? I blasted them with compressed air more than once..

If you go wide open the bike launch but feels not so fast as it used. Going down it struggle to keep idle and bogs a lot.
Did a full carb rebuild with new rings, new gaskets and so on.
Cleaned jets ans all passages..
Checked boots and did alignment.
No big differences
Replaced air filter with new oem unit, correctly oiled.
New plugs, also tried the fuel pump mod suggested here, no difference, tried swapping coils with cbr ones with mod suggested here no big difference.
Bike is fully oem, no modification.. only carb trumpets are a little shorter because oem become hard as rock and deformed and replaced with some I made with lathe and milling machine.. but did years ago and never had a problem with that.

The last winter I did also a full engine rebuilt.
Replaced all sealings, did the valves, pistons, checked barrels, new rings, new everything. Engine is now almost brand new.

But problem is still there.
I dont really know where to look at...I am desperate and loosing the will to ride her again. But I dont want to surrender, we did together so many nice rides..

Here no one knows those bikes so i dont really know who to ask..
Anyone has an idea??
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Posts: 2591
Joined: Sat Sep 24, 2011 3:27 pm
My Bike: ZXR400 L4
Location: Nuneaton

Re: Bike running fine cold and very bad when warm

Post by banner001 »

Sounds like it's running too rich, so as the bike warms up it just gets are going to have to fully go through your cards and check everything. Look for any fuel leaks past the float needle, maybe try setting the floats to 13mm.

Get a compression tester, and check all spark plugs...this will help you to narrow it down to what is probably just the carbs.

I would also check to make sure you have not kinked a fuel pipe, or have a blockage in the line or in the tank
UK ZXR400 L3 (1993) - Fully restored and on the roads, my green beast!
JPN ZXR250 A2 (1990) - Revs to 19,200rpm... 'nuff said :smt003
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