Bike not running well at higher revs

[CBR250]

Hi All

I am converting bike 94 CBR 250RR MC22 for track, I have recently stripped it down and replaced the rear shock, done the 53/14 sprocket mod, rims off for track tyres etc. Didnt touch engine/carby, except for replacing spark plugs. I have cut away sections of the wiring loom as it dosnt need lights/indicators side stand etc. It isn't using the instrument cluster or speedo/rev light cluster either.

I had to find and join the side stand circuit in the wiring loom for the bike to run, I also joined the clutch circuit.

Bike starts and runs in the low rev range fine. Anything above im guessing 6k (no rev gauge) it continues to rev but has strange higher pitch to the sound and dosnt have the same power. even worse under load. I have taken the carbys off and cleaned all the jets.

Is there a circuit that needs to be joined for a rev/speed limiter or something? I have replaced the fuel and filter. All spark plugs have spark. all headers evaporate water.


Any help much appreciated.

Cheers
Reece

[tigertim20]

cleaned the air filter?

[CBR250]

No, haven't cleaned air filter yet, although it runs the same with no airbox or filter.

[nodrog]

Don't those old import jap bikes need the speedo to function properly? or is that only on the adult sized bikes?

[FJRider]

No, haven't cleaned air filter yet, although it runs the same with no airbox or filter.

Different causes ... often get the same/similar result.

Clogged air filter makes it run over rich.

NO air filter makes it run lean.

I assume the ...


done the 53/14 sprocket mod

means you have geared it to run at lower revs at the same speed ... ??? (with the idea you can go faster in high gear)

[CBR250]

Different causes ... often get the same/similar result.

Clogged air filter makes it run over rich.

NO air filter makes it run lean.

Yeah its possible, I'm willing to try anything as running out of things to try.


I assume the ...



means you have geared it to run at lower revs at the same speed ... ??? (with the idea you can go faster in high gear)

It's a common mod for the cbr 250. Basically just shifts the power to lower range. Equals more acceleration less top speed.

[FJRider]

... Equals more acceleration less top speed.

Higher speeds in the lower gears maybe ... but higher rev's in each of the gears to get it.

Also ... less power available in/at the top speeds. (How many km's on the engine .. ??)

Maybe look at re-jetting and after-market air filter ...

[Akzle]

Hi All

Bike starts and runs in the low rev range fine. Anything above im guessing 6k (no rev gauge) it continues to rev but has strange higher pitch to the sound and dosnt have the same power. even worse under load. I have taken the carbys

fucked clutch

[mossy1200]

vfr400 did the same thing to me when I removed the speedo. Could be a Honda thing of that age. Best google a resistor mod to get it sorted.

[SVboy]

Don't those old import jap bikes need the speedo to function properly? or is that only on the adult sized bikes?

This sounds correct

[CBR250]

vfr400 did the same thing to me when I removed the speedo. Could be a Honda thing of that age. Best google a resistor mod to get it sorted.

Thanks everyone for your help.. this was the issue with a speed limiter built into the speedo. Just needed to find the circuit and connect it to the 12v with a 3.3k resistor in series. Runs fine now, Cheers mossy

[mossy1200]

Thanks everyone for your help.. this was the issue with a speed limiter built into the speedo. Just needed to find the circuit and connect it to the 12v with a 3.3k resistor in series. Runs fine now, Cheers mossy

Nice mine got to about 7tho revs and felt like it dropped 2 cylinders. Possibly even the same speedo unit on both.