AMA membership required?

[lumpy]

Do I have to join AMA to race at BUBB or ECTA?

[AHG]

Being an AMA sanctioned race event, that would be a yes for the Bonneville Motorcycle Speed Trials.  

[Seldom Seen Slim]

As for the other venues --- ECTA, SCTA/BNI, LTA, etc -- no, you don't need AMA membership.

Strictly speaking, the BUB event doesn't exist any more.  It has been superseded by the BMST (Bonneville Motorcycle Speed Trials).  Many of the same folks and operating procedures -- just new management.

[Stainless1]

But you do need to be a member of whatever organization you are racing with

[wobblywalrus]

A lot of this has to do with liability.  A club race among members is less subject to adverse litigation than a club holding a race for the general public.  Years ago our dirt bike club priced insurance for both of these options and the second was much more expensive.  We run an AMA sanctioned event every year and all participants are AMA members.  Doing this is the only way we can afford the insurance.