Re: Russian Motor in a 31 Cabriolet
Just because the valves appear to open and close properly, at speed they may be sticking slightly and not closing all the way before combustion takes place thus producing the back-fire. The valve(s) may not be seating properly either and need lapped (or replacement). Did you try some MMO as mentioned earlier? A compression and leak-down test might be helpful in this instance. A bad distributor cap can cause a "cross-fire" situation, but since you mentioned trying a modern distributor you can rule that out. The Zenith has a filter screen inside that could be plugged, maybe just crud partially blocking something in the carb. Do you belong to an A club? Borrowing a known good carb would be nice to try. Looks loke a nice car, don't give up on her!
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