Carburation problem under 4000 rpm

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Davi91
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My Bike: ZXR 400 L6

Carburation problem under 4000 rpm

Post by Davi91 » Tue Jun 20, 2017 5:48 pm

Hi, i'm a happy possessor of a kawasaki zxr 400 L year 1996, but from the first moment when i buyed it, have a problem with carburation. It has difficult to start when engine is warm and under 4000 rpm, when is on road (it's indifferent between warm and cold), it kicking, coughing, and if i open for 2/3 - 3/3 the gas knob for accellerate, the engine goes off. For surpassing 4000 rpm, i must open the gas knob for 1/3 and when the engine is over 4000 rpm, the engine is perfect, run very well up to the limiter.
If i close the fuel tap or when the fuel is about to end, the engine running well even under 4000 rpm. Please help me to find the problem. Sorry for my bad English

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banner001
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Re: Carburation problem under 4000 rpm

Post by banner001 » Wed Jun 21, 2017 2:55 pm

It sounds like your bike is too rich on the idle circuit, so you are getting too much fuel into the engine, you need to locate the 4 pilot screws located on the carbs and turn each one clockwise (i.e. screw them in) by 1/8 of a turn, then go for a ride and see if it improves. You may have to do this 2-4 times to get the bike to be better under 4k.

However this might now mean that the bike isn't getting enough fuel when you go over 4k, if this turns out to be true we can help you with that as well.
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Davi91
Posts: 8
Joined: Tue Jul 21, 2015 2:17 pm
My Bike: ZXR 400 L6

Re: Carburation problem under 4000 rpm

Post by Davi91 » Wed Jun 21, 2017 4:10 pm

banner001 wrote:
Wed Jun 21, 2017 2:55 pm
It sounds like your bike is too rich on the idle circuit, so you are getting too much fuel into the engine, you need to locate the 4 pilot screws located on the carbs and turn each one clockwise (i.e. screw them in) by 1/8 of a turn, then go for a ride and see if it improves. You may have to do this 2-4 times to get the bike to be better under 4k.

However this might now mean that the bike isn't getting enough fuel when you go over 4k, if this turns out to be true we can help you with that as well.
Hi thank you very much for the answer, i appreciate the help. Can you tell or show me where is the pilot screw?

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banner001
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Re: Carburation problem under 4000 rpm

Post by banner001 » Thu Jun 22, 2017 6:02 pm

I did a stripdown post a while back, the screw is shown on here where I say it should be between 1.5 to 2.5 turns out from fully in.

viewtopic.php?f=115&t=14018
UK ZXR 400 L4
UK ZXR 400 L3 track bike
1989 FZR 1000 EXUP-R streetfighter

Davi91
Posts: 8
Joined: Tue Jul 21, 2015 2:17 pm
My Bike: ZXR 400 L6

Re: Carburation problem under 4000 rpm

Post by Davi91 » Thu Jun 22, 2017 9:57 pm

banner001 wrote:
Thu Jun 22, 2017 6:02 pm
I did a stripdown post a while back, the screw is shown on here where I say it should be between 1.5 to 2.5 turns out from fully in.

viewtopic.php?f=115&t=14018
Thank you, now i understood. For regulation without disassembled the fuel tank, does need the pilot screw adjustment tool? I buyed it but not the original because it is most expensive.

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banner001
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Re: Carburation problem under 4000 rpm

Post by banner001 » Thu Jun 22, 2017 10:14 pm

No, if you remove the carbs you can use any flat blade screwdriver.

If you don't remove your carbs, you just need a small 2-3" screwdriver so it can gain access to the screw head.

Be careful, they are brass and can be damaged easily. If you are unsure then you need to remove the carbs.
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1989 FZR 1000 EXUP-R streetfighter

Davi91
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Joined: Tue Jul 21, 2015 2:17 pm
My Bike: ZXR 400 L6

Re: Carburation problem under 4000 rpm

Post by Davi91 » Thu Jul 13, 2017 10:53 pm

Hi, i resolved the problem just cleaning the carbs and adjusting the float height (was 8mm, now i set 11mm like as manual). Thank you very much :excited

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banner001
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Re: Carburation problem under 4000 rpm

Post by banner001 » Fri Jul 14, 2017 12:03 am

Yeah, that will do it, 8mm will be very rich throughout the whole rev range. You might need to compensate through the midrange and top end or you might be lucky
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Davi91
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Re: Carburation problem under 4000 rpm

Post by Davi91 » Tue Jul 18, 2017 3:42 pm

Hi, i sang victory too soon, i did the insurance to test it on the road and I noticed that when the engine is warm it has the same problems. Now they are attenuated, but they have not disappeared :smt010
The pilot screw are 2 turns from close (as by manual dynojet). If i change the pilot screw settings, it get worse. I have tested 1 + 1/2 turns from close, 1+ 3/4 from close and 2 + 1/2 from close and there have been no improvements.
I thought the problem could depend on the diaphragm, they are very soft, the gum is almost worn but no holes. Or they could be the valves shim :smt017

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banner001
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Re: Carburation problem under 4000 rpm

Post by banner001 » Wed Jul 19, 2017 6:57 pm

are you using dynojet needles?

if so these are a smaller diameter than stock and do cause it to be a bit rich down low...though if you are always using them for top-end then it makes no difference what the pilot circuit is doing.

as for the valve clearances, it can make the bike hard to start, and yes if they are all grossly out its similar to having too much valve overlap...so a lumpy idle.

i would isolate your problems, so check the chain tension/tensioner/blades, make sure the timing is correctly set, check and adjust to the loose end all the valves, new fuel filter, remove the tap from your fuel tank and clean the small inline filters, make sure your carbs are thouragly cleaned, check your make and quality of air filter, airbox-to-carb seals, downpipes, exhaust can...then you can start on your fuelling once you know everything else is fine.

im going to be buying a modified air-fuel probe that datalogs and can be situated down in your exhaust without the need for welding a nut on your downpipes...ill have to see how it goes...
UK ZXR 400 L4
UK ZXR 400 L3 track bike
1989 FZR 1000 EXUP-R streetfighter

Davi91
Posts: 8
Joined: Tue Jul 21, 2015 2:17 pm
My Bike: ZXR 400 L6

Re: Carburation problem under 4000 rpm

Post by Davi91 » Sun Jul 23, 2017 10:39 pm

Yes, i have dynojet needles but i don't have the original needles for try the difference. I buyed the bike with pre-installed dynojet kit. I would like to solve this problem, because over 4k rpm it's perfect. When the engine it's cold and after a few minutes when i close the fuel tap, the engine runs perfect until finish the fuel.

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