ORIGINAL: pe reivers
If the velocity stack has an angled entry It may be important which way the angle points. With a straight ended stack, using an air dam can create as many problems as it intends to solve. Mostly due to creating a vacuum at the carb mouth.
Condemn?? Heavy words.
I agree 100% with what you are saying Pe. That is why I suggest trying as many things as possible to resolve the issue. On more than one occasion, I have seen a fix, that for all purposes, should not have worked but it did. When an engine installation is completed using all the known proper practices and there is still a problem, one gets desperate and will try anything to resolve the issue.
As far as creating a vacuum at the air intake, while perhaps off subject, I have often wondered about the rear facing air intake horn used on some 3W engines. I would believe that would create a constant low pressure at the carb inlet.
Condemn ..... heavy perhaps, but when I see people piling on a guy for making a suggestion that I have seen work I get a bit upset. Perhaps I should have said criticize rather than condemn.