Webb flapper leak
 

Mine is also a Webb. Not too many around, I would imagine. I don't think it is lifting enough to leak and it runs very good, accelerates good, no stumbles. You should search on vacuum leaks, hesitation and/or rough running to see if it matches your running condition. Vacuum leaksare the culprit, very often. My airbox flapper is held down in all four corners by bolts. They are pinned to prevent back out, but you may be able to adjust them and the springs to hold the flapper down tighter. At least that would help to eliminate that as the problem. My only other suggestion is to verify that your timing is correct and that your distributor is advancing properly. If the advance weights/springs are not working properly the result can be what you're describing. (just had this happen) Search for Gunters thread regarding rebuilding/cleaning distributors.

http://forums.pelicanparts.com/uploa...1180224340.jpg

inadvertantly started this new thread while trying to reply to an existing one. Operator error.

Al

Thanks again Al. Your airbox is identical to mine. I'll see what pops up on the forum, do some more troubleshooting and let you know what I find.