I have a 2002 300EX that has been bored out to a 330cc. It starts up and idles great, but when you get in the higher rpms it cuts out. I didn't know if this would be a timing issue, a valve issue, or possibly just needing to run a high octance fuel. Any help would be greatly appreicated.

Thanks.

 

High octane fuel would only be needed if the compression has been bumped up with the big bore. That is a possibility.
Also you will want to check the jetting. The main jet (top end jet) may be too big if it bogs down at full throttle.
Do you know how to do a plug chop?

 

I believe it is running a bit higher compression. It used to run just fine in the same setup about a year ago. I have no idea what a plug chop it though. I just though that something such as the valve or anything had become unadjusted and would cause this.