99 ZX6 - flat spot at 7500rpm - Any help?

[zx6chris]

Hi
I've recently picked up a 99 zx6, and was wondering if it's normal for there to be a fairly noticeable flat spot at about 7500rpm?
Now just to clarify, it's not so noticeable if you're riding hard from a standing start, but is really there if you're trying to accelerate from speed (to overtake for example).
I thought it could just be my riding style as I get used to the bike, but I loaned it to a mate who's heaps more experienced than me, and he agreed about the flat spot.
Before I picked it up, it had been sitting for about 3-4 years not started, so I got the carbies cleaned and serviced, drained the old fuel, and ran it. is it possible it's just sucked some crap into the carbies and I need to get them cleaned again?

Any advice is appreciated thanks.

[Disco]

Maybe Jason (life of crime guy) could post up his chart from the last dyno day I think his was an '09 zx6r.....It pulled aroud 100hp I think...But it would give you an idea of the curve on one.....

[Magpie]

mate i was doing the same thing on my 98 ZX6 just this arvo and i agree, around the 7g mark it seems to be a no mans land

[SnypR]

When l had a flat spot (around 3-4000) a carb sync fixed the problem

[Gosling1]

It could be the exhaust system type ?? Unless the system has been jetted properly, flat-spots when using some styles of exhaust are not uncommon....a carbie synch is also a good idea. Also make sure the air filter is clean....

[timmyrocks]

flat spots in that rev range point to needle position, ( if its the carbs) is agree wid goss, does it have different exhaust, maby its not setup for the extra fuel at the rev range????

[zx6chris]

It could be the exhaust system type ?? Unless the system has been jetted properly, flat-spots when using some styles of exhaust are not uncommon....a carbie synch is also a good idea. Also make sure the air filter is clean....

It has a stock system and the jets were replaced less than 2000km ago. They said at the bike shop that they did a full carbie service including sync. I'll try replacing the air filter and see how it goes, it seems like a cheap place to start! If that doesn't work I guess it's back to the bike shop to question what they did (or didn't) do to it when I got it!

Cheers

[mike-s]

does it seem to occur more at specific revs or at specific throttle openings? have a bit of a play and try and figure this out. Specific revs MAY be electrical. Specific throttle openings is very much looking at the carby. Also try and determine the specific percentage of throttle opening when it occurs, it will help track down what the contributing causes would be (idle jet, float height, main jets, needle height, so on so forth).

[zx6chris]

does it seem to occur more at specific revs or at specific throttle openings? have a bit of a play and try and figure this out. Specific revs MAY be electrical. Specific throttle openings is very much looking at the carby. Also try and determine the specific percentage of throttle opening when it occurs, it will help track down what the contributing causes would be (idle jet, float height, main jets, needle height, so on so forth).

OK... So Ive given it a good couple of weeks run going to work and back, and taken it on a long ride to Coffs Harbour and back. It's still got the flat spot. It's a bit hard to tell if it's throttle position or revs exactly, but I've tried slowly winding it up, and it seems to go alright, so I'll guess it's the throttle position.
It seems to be a little doughy at about 1/4 throttle, and worse when close to wide open.
so what next?

[Bogan]

My 750 has a flat spot at 8k, it's in getting tuned as we speak so I'll have a chat to the guy when I pick it up next monday if you like and post back here. I've got a Yoshi bolt on (and apparently a fairly tired engine) and otherwise stock bike, and a new air filter.

Will let you know what if anything he finds with mine.

[Six Addict]

does it seem to occur more at specific revs or at specific throttle openings? have a bit of a play and try and figure this out. Specific revs MAY be electrical. Specific throttle openings is very much looking at the carby. Also try and determine the specific percentage of throttle opening when it occurs, it will help track down what the contributing causes would be (idle jet, float height, main jets, needle height, so on so forth).

OK... So Ive given it a good couple of weeks run going to work and back, and taken it on a long ride to Coffs Harbour and back. It's still got the flat spot. It's a bit hard to tell if it's throttle position or revs exactly, but I've tried slowly winding it up, and it seems to go alright, so I'll guess it's the throttle position.
It seems to be a little doughy at about 1/4 throttle, and worse when close to wide open.
so what next?

throttle position will always be relatively close to revsi'd have thought

[mike-s]

Throttle position only drives the butterflies, the diaphragms will rise according to demand so there will always be a slight bit of lag at least. the higher the gear, the less directly related throttle position will be related to the engine revs due to the demand from the taller gearing.

[Bogan]

My 750 has a flat spot at 8k, it's in getting tuned as we speak so I'll have a chat to the guy when I pick it up next monday if you like and post back here. I've got a Yoshi bolt on (and apparently a fairly tired engine) and otherwise stock bike, and a new air filter.

Will let you know what if anything he finds with mine.

Jets was what fixed mine, it's like having a new bike.