Here is my problem. I have a sbc 400, no, that is not the problem! The engine runs on 6 cylinders and usually after a 15 minute warm up, (this includes a drive and acceleration), it will finally run on 7or 8. I have narrowed it to be the rear two cylinders, 7 and 8. Therefore I have deducted that I have a common problem and it points at the secondary circuit on my 830 annular boost Holley. I removed the carb and found that all four booster (I’m not sure on the term, but I am referring to the four pods which are in the centre of the venturies) were loose and especially the rear two, so I secured them. At the same time I noticed that my nitrous plate had the rear plug loose but there is no way of a vacuum leak here. This plug is from the inside of the plate and fits the distribution pipes securely in the area where the nitrous is fed into the plate. I tapped it back in place, put it all back together and it ran wonderfully. I took it for a drive, had it back fire, and it started all over again, running on 6.

I took the carb off, noticed that the plug was loose once again so I tapped it back in place, and installed a new 870 vacuum Holley and it runs great once again. With this carb there is no backfire.

So I‘m wondering if a slightly loose pod can cause this condition? Anyone familiar with this? Thanks.