Distributor Recurving?

I don't mean to hijack your post .... sorry !
I just got done recurving my single point distributor for my 273 .. put a 8* slotted plate in and it had already two light oem springs in it.. Got it all timed in 18* intial and between 34-36 total*and when I hook the vac line up to the dist it will won't stay running smooth and when you give it some gas it fights itself bucking up and down on the throttle.. the when I disconnect the vac line it runs fine.. must be a faulty vac. canister right ? it's a 9.5 diaphram .
I'm not going to run the vac. adv. anyway But...just like to know .
other wise... It maid a biggggg difference overall .
I have a pertronix III coming to install into it with built in rev limiter.