Well that's not entirely true. It will when revved at standstill but won't while accelerating on it. It's an FZR400 3tj fitted with an FZR600 4jh engine with FZR600 3he carbs and a standard 3tj exhaust on it. Unsure which model the ignition system is from. So far have tried a bigger fuel pump, checked the carb diaphrams and tried both open and closed exhausts on it. There is no exup valve on the front pipes to be jammed closed.

It has reasonably good acceleration lower down but fades towards the 8k mark. Could the ignition be at fault or would the carbs limit it (can't quite see how) or is it possibly symptomatic of some deeper issue? Maybe the front pipes are from the 400cc engine and are restricting it? Or possibly the cdi is not functioning properly?

Thoughts, suggestions, similar experiences and any pointers to what may be causing this appreciated. Baffling the hell out of me. If I don't have at least some idea of what to look at I could well end up replacing everything...

Liam

Possible binding brakes, or with the engine change did you change the sprocket set as or are they the same.Different sizes of chain sproket will give different performance characteristics.

Possible binding brakes, or with the engine change did you change the sprocket set as or are they the same.Different sizes of chain sproket will give different performance characteristics.

Hi, the problem does seem to be the sprockets. The gear ratios are way too low. Have spent a week trying to locate an off-the-shelf sprocket set that would fit the 600 engine and 400 wheel but without success so have got B+C express to machine a rear one for me that will convert it to a 530 chain also.

You're using an FZR600 wiring harness to run the 400 motor. They will interchange by fit alone (pins and receptacles), but the 600 CDI box will not properly fire the 400 motor. It won't rev past X,000 RPMs (I can't remember the actual number). We run into this every once in a while on the club racing circuit I run. I have one spare 400 box that I know of, and they're pretty rare. The 600 boxes are far more common and may people sell them claiming interchangeability. They aren't.