I have a 1981 Gazelle kit car built on a 1969 beetle chassis with a stock Bosch distributor. New this year, its been loosing power at the top end of third and forth gear and then backfiring. This only occurs once its been running for around 10 minutes. It idles fine and will even red line in neutral without a backfire. Dwell is 50 and points are new and set to .016". I found some discrepancy about timing though. Should it be at TDC or 7.5 BTDC? When set to TDC it backfires at about 2900 RPM consistently so it is now set at 7.5 BTDC. Thoughts on vapor lock? I'm pretty sure my rear main seal is leaking some; could this some tie to it? It has an aux oil cooler and even and electric fan to aid with circulation.
I know this isn't a purist VW but, my baby isn't feeling well and I'm dieing here. Any help will be greatly appreciated!