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Hello- > I did another tune up today: adjust timing to 10s BTDC, set points to 49s, > idle at 850rpm and mixture set. I fiddled with the accelerator pump a bit to > set it up how the manual says when experiencing a flat spot. I checked the > vacuum advance and that works fine, I set the valves 2 weeks ago. I haven't > checked the compression yet, I will do that when I next get a chance. > > Any suggestions? I hate to tell you this, but one of the most common reasons that you backfire through the carb is because of a major compression leak, often having to do with valvetrain. Before you continue to pull your hair out, at *least* do a poor-man's compression check. Disconnect the points lead from the coil and turn the engine over with the starter, paying careful attention to the four pulses you hear. If all four pulses are the same length, then compression *probably* isn't the cause of the major backfiring. If you hear one or more fast pulses, you found your culprit. You have a major compression leak, and no amount of igntion and carburetor tuning will help. If this is the case, the first thing to do is double-check your valve adjustment. If you have a valve that's too tight, it will cause the compression leak (obviously, since the valve isn't closed :-). If this doesn't help, then do a complete compression check, find the culprit cylinder, and rip out the engine. Hopefully this isn't the problem! Take care, Shad Laws LN Engineering - Aircooled Precision Performance http://www.lnengineering.com ------------------------------------------------------------------- List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org