'70 318 BBD falls flat under load

Pulled the airhorn off and looked around. The spring under the step up piston is there and it all moves freely. The accelerator pump looks new. I can only assume that it's the correct part. It's the leather type.

Checked for vacuum leaks with carb cleaner and water. Everything on the exterior seems to be ok as far as that goes.

I bought the rebuild from National Carburetors. A couple buddies recommended them based on their experiences. I had planned to install it as soon as I got it but then got rear ended and it got put on the back burner so it's just past the warranty now. I'll still call them on Monday but if anybody else has some ideas I can check.

I was hoping to go for a drive on Sunday. Beautiful fall weather. I can drive it but I'd rather not kill it at an intersection and have some joker hit me in the rear again.

Thanks.