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[sorted] ZX6R F series not ok between 4-7k rpm but good between 1-4k and 7k to redline

764 Views 52 Replies 5 Participants Last post by  Brandon35
Hello everyone,

I have an F series ZX6R and I am unable to figure out what is wrong... Can someone help me? 馃槵

Here is the situation:
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...

Any help is appreciated 馃憤 please.

Thank you!!!!
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you are still missing information on things such as;

engine temp
ambient temp
throttle position vs load condition
mileage and then of course you mention unknown valve clearances, which also means unknown state of tune!
you fail to mention if all stock components in the carbs or if anything has been changed
How they were cleaned, if they are truly clean.most people have zero clue how to truly clean carburetors and even fewer still actually do it correctly and thoroughly

etc

but it sounds like..........


nevermind, I will wait for answers.......
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Thank you mate

Yes you are right:

Engine temp working temperature needle is half way I can't give you the exact temp.
Ambient temp 18 deg C
Always full throttle and full load at acceleration (not 100% sure what you mean here.)
Unknown mileage
Carb jets are all stock
I cleaned the carbs with air pressure and carb cleaner - tbh Ive put some effort in the carbs...
Thank you mate

Yes you are right:

Carb jets are all stock
I cleaned the carbs with air pressure and carb cleaner - tbh Ive put some effort in the carbs...
Rivers is not going to let you call that. 鈥淧utting in some effort鈥
Maybe this could be useful: airbox carbs, jets and needles are OEM. But the bike as a full akrapovic pipes and muffler...
If your issues are at speed, I wager your issue is either improper airbox tube routing, or a faulty air valve (metal housing that connects the air-box to your float bowls).

If your tube routing is not the issue, suggest you do the "airbox mod" and delete the likely faulty air valve. [Edit] The valve uses the airbox's POSITIVE pressure AT SPEED to allow fuel to flow through the jets, opening and closing to adjust for the load setting. This adjustment via opening/closing the valve is a marginal method of fuel emission control from what I understand so... I don't run it anymore.

If you want to do the airbox mod and delete a point of failure:

1) remove your tank
2) remove airbox cover (the top hose that leads towards the front of the frame is the hose you want to focus on)
3) remove bottom half of airbox
4) take the valve housing connected to the hose the leads to the top of the airbox off.
4) run a T-splitter from the two hoses coming from the carburator into the air-box hose (they are different diameters); make sure they are secure
5) re-install airbox and tank
6) go ride

[Edited the ram-air pressure error]
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2
Thank you I think you are on something here!!! I had all hoses coming from the carburettor boots tapped by a plug got no idea what previous owner did... I've found some spare parts and tried to put the thing back OEM is this the correct set up? so you would like me to connect these 'A' hoses into the 'B' hose there ?

Thank you so much for your help.


Edit: ) run a T-splitter from the two hoses coming from the carburator into the air-box hose (they are different diameters); make sure they are secure.

Ok I've actually figured out which hoses you are referring too they are not the ones in the picture - now trying to find a T junction thingy and will try out

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If your issues are at speed, I wager your issue is either improper airbox tube routing, or a faulty air valve (metal housing that connects the air-box to your float bowls).

If your tube routing is not the issue, suggest you do the "airbox mod" and delete the likely faulty air valve. The valve allows the airbox's negative pressure to help pull a vacuum in the carb to allow the fuel to flow through the jets, opening and closing to adjust for the load setting. This adjustment via opening/closing the valve is a marginal method of fuel emission control from what I understand so... I don't run it anymore.

If you want to do the airbox mod and delete a point of failure:

1) remove your tank
2) remove airbox cover (the top hose that leads towards the front of the frame is the hose you want to focus on)
3) remove bottom half of airbox
4) take the valve housing connected to the hose the leads to the top of the airbox off.
4) run a T-splitter from the two hoses coming from the carburator into the air-box hose (they are different diameters); make sure they are secure
5) re-install airbox and tank
6) go ride

^^^ from your post....... ^^^^ The valve allows the airbox's negative pressure to help pull a vacuum in the carb to allow the fuel to flow through the jets, opening and closing to adjust for the load setting. This adjustment via opening/closing the valve is a marginal method of fuel emission control from what I understand so... I don't run it anymore.


NO NO NO NOT just NO but fucking stupid NO


The float bowls are pressurized at speed !!!!!!! there is not vacuum in the bowl. that would try and hold the fuel in the bowl!!!!!

The airbox on all RAM AIR BIKES!!!!!!!!!!!!!!!! also is pressurized at speed, it isn't a fucking vacuum!!!!!!!! geezus fucking christ
鈥︹ make that the fifth attempt, lol. The advice is good, the explanation is not鈥
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^^^ from your post....... ^^^^ The valve allows the airbox's negative pressure to help pull a vacuum in the carb to allow the fuel to flow through the jets, opening and closing to adjust for the load setting. This adjustment via opening/closing the valve is a marginal method of fuel emission control from what I understand so... I don't run it anymore.


NO NO NO NOT just NO but fucking stupid NO


The float bowls are pressurized at speed !!!!!!! there is not vacuum in the bowl. that would try and hold the fuel in the bowl!!!!!

The airbox on all RAM AIR BIKES!!!!!!!!!!!!!!!! also is pressurized at speed, it isn't a fucking vacuum!!!!!!!! geezus fucking christ
Forgive the backwards logic on that part, I got excited while I was drinking a few to many brewskies.

Positive pressure in float bowls, negative pressure in the throat of the carb, fuel moves through the jets. Lack of pressure in the float bowls equals no fuel movement.

For the OP, regardless of my backwards pressure logic, that valve is still a failure point.
Thank you I think you are on something here!!! I had all hoses coming from the carburettor boots tapped by a plug got no idea what previous owner did... I've found some spare parts and tried to put the thing back OEM is this the correct set up? so you would like me to connect these 'A' hoses into the 'B' hose there ?

Thank you so much for your help.


Edit: ) run a T-splitter from the two hoses coming from the carburator into the air-box hose (they are different diameters); make sure they are secure.

Ok I've actually figured out which hoses you are referring too they are not the ones in the picture - now trying to find a T junction thingy and will try out
Right, the 4x capped ends are there so you can attach a carb sync tool; those are connected to the carb boots, not the carbs themselves
vacuum. Pressure. Ahhhh. Semantics. 馃ぃ馃槀


I love it when Lloyd chimes in ripping us morons a new one. 馃ぃ馃槀馃ぃ
鈥︹ make that the fifth attempt, lol. The advice is good, the explanation is not鈥
Ha well, it wouldn't be me if I was 100% correct now would it. I call it a learning tool 馃し馃徎鈥嶁檧锔
vacuum. Pressure. Ahhhh. Semantics. 馃ぃ馃槀


I love it when Lloyd chimes in ripping us morons a new one. 馃ぃ馃槀馃ぃ
A long time ago, I did a lot of research on Ram-Air. At one point, there must have been bleed-over from simultaneously learning about Bernoulli's principal (faster air = lower pressure) and bingo - drunk me splices them together in one little phrase to make me sound like a moron.

We have fun here
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A long time ago, I did a lot of research on Ram-Air. At one point, there must have been bleed-over from simultaneously learning about Bernoulli's principal (faster air = lower pressure) and bingo - drink me splices them together in one little phrase to make me sound like a moron.

We have fun here
It happens. I tend to be a little smarter in real life than online lol.
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OP your right side smog valve hose is disconnected if you did not notice.

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If you want to further reduce complexity, you can also do the "smog delete".

At the top of the engine towards the frame is a cylindrical valve connected to two plates via short hoses, with one tube running to the throttle side of the airbox. You can delete this system entirely, as it only serves an emmissions purpose (dumps airbox air into the exhaust when you decel to ignite unburnt fuel).

1) on the airbox, cap the fitting that the hose to the smog valve runs to. Make sure it's secure because it can contact the carb/throttle cables if you're not careful.

2) Cap all 4x of the tubes coming from the carb boots. I suggest you turn the boots 180 degrees so you can access those fittings with a sync tool without needing to remove the airbox.

3) remove the smog cylinder valve

4) you can connect the two short hoses from the engine caps together, OR you can buy "smog block-off plates" to make it look even cleaner.

Keep your old parts, never know if you need something till you throw it away and wish you kept it (ask me how I know).
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Forgive the backwards logic on that part, I got excited while I was drinking a few to many brewskies.

Positive pressure in float bowls, negative pressure in the throat of the carb, fuel moves through the jets. Lack of pressure in the float bowls equals no fuel movement.

For the OP, regardless of my backwards pressure logic, that valve is still a failure point.
I ran out of any forgiveness about 5000 idiotic stupid posts ago (from all the idiots).
vacuum. Pressure. Ahhhh. Semantics. 馃ぃ馃槀


I love it when Lloyd chimes in ripping us morons a new one. 馃ぃ馃槀馃ぃ
It is not semantics though.

It is incorrect information being doled out to the masses (most are dumb) and then they run with that incorrect information.......

I am just here doing my part to increase the intelligence of the masses and nip the dumb fucking shit in the bud!

easy solution to the last part...... don't be a moron!?! I know simply concept, too bad reality is, society has been filled and bred by so many morons it is impossible to rid them all now- they are the biggest breeding population just producing more and more morons
I'll do a test run tomorrow and keep everyone posted ;-)
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