m400 EFI TUNE with big bore

[xinlu]

Hi guys,
I'm currently running a KTM 525 EXC engine in an FSAE car. It is a single cylinder with a stock displacement of 510cc and has been converted from carburettor to EFI through a 12-2 trigger wheel and a motec m400 ecu. It has been upgraded to 540cc through a big bore. Prior to upgrading the bore, there was a tune done for it and it ran like a dream. After the big bore, i increased the fuel through the overall trim of about 15% and it runs and revs but when driving there seems to be a lack of power up top and it doesn't seem to rev out higher than 7k rpm. There also seems to be a throttle delay before and after throttle is opened and closed. I've tried playing around a little with the fuel and timing maps but can't seem to rectify the issue. I was told by the dyno shop that a big bore shouldn't really affect the tune that much, just an increase in fuel is needed.

Any help and advice is greatly appreciated. Thanks!

[Sean]

You have increased the capacity by just under 6% yet you have increased the fuel by a 15% overall trim. There is your problem. Potentially it will need no more fuel at closed throttle and the demand for extra fuel will increase from there. Don't mess with the timing if it ran well before. The changes in fuel demand will likely not be linear, the bigger capacity changes how the cylinder fills etc etc.

I would recommend: Get it tuned professionally by the shop that previously tuned it well.