ninjette.org - View Single Post - Flat spot in power curve between 6-7,000rpm

austinninjabill · March 15th, 2018, 11:35 AM

Thanks to everyone who has provided advice so far as I get this '92 250r running after sitting for 15-16 years.

Still no brain bucket (arriving today: full face Evel Kinievel red, white and blue), but am getting a little more confident zipping around on it. Can now get up to about 65-70 before backing off.

Still takes a long time to warm up without bogging and the choke still has no friction at the lever. And I am having to adjust idle just a bit after every few rides.

All that will get sorted out, however, the bike has a funny behavior that I was wondering whether anyone else has seen/corrected.

It will pull smoothly and strongly to about 6,000 rpm, then the power curve flattens 'til around 7,000, where it suddenly takes off like a banshee right up to redline.

Makes the bike a little unruly/disconcerting to ride, having a "lull" then a "bang" right in the middle of the rpm range. When it hits that 7,000 sweet spot, if you're not paying attention and holding on tight, the bike could leave you sitting on the pavement, which is going to hurt a bit at 50mph.

Guessing this is a carb/air-fuel delivery issue?

Again I am running the following setup:

K&N Pod (what a throaty noise that thing makes)
Slow jet: 40
Main Jet: 110
Shims: 1
Air screws: 2.5 turns out (left and right)

Based on above setup, any thoughts as to what might be causing this flat part of the power curve? Guessing the slow jet isn't the issue once above above idle, same with air screws. So do I need it richer (112 and 2 shims) or leaner (108 and no shims) or something in between?

March 15th, 2018, 11:35 AM	#1
austinninjabill ninjette.org member Name: Bill Location: Central Texas Join Date: Jan 2018 Motorcycle(s): 1992 250R Ninja Posts: 27	Flat spot in power curve between 6-7,000rpm Thanks to everyone who has provided advice so far as I get this '92 250r running after sitting for 15-16 years. Still no brain bucket (arriving today: full face Evel Kinievel red, white and blue), but am getting a little more confident zipping around on it. Can now get up to about 65-70 before backing off. Still takes a long time to warm up without bogging and the choke still has no friction at the lever. And I am having to adjust idle just a bit after every few rides. All that will get sorted out, however, the bike has a funny behavior that I was wondering whether anyone else has seen/corrected. It will pull smoothly and strongly to about 6,000 rpm, then the power curve flattens 'til around 7,000, where it suddenly takes off like a banshee right up to redline. Makes the bike a little unruly/disconcerting to ride, having a "lull" then a "bang" right in the middle of the rpm range. When it hits that 7,000 sweet spot, if you're not paying attention and holding on tight, the bike could leave you sitting on the pavement, which is going to hurt a bit at 50mph. Guessing this is a carb/air-fuel delivery issue? Again I am running the following setup: K&N Pod (what a throaty noise that thing makes) Slow jet: 40 Main Jet: 110 Shims: 1 Air screws: 2.5 turns out (left and right) Based on above setup, any thoughts as to what might be causing this flat part of the power curve? Guessing the slow jet isn't the issue once above above idle, same with air screws. So do I need it richer (112 and 2 shims) or leaner (108 and no shims) or something in between?