Straight 8 backfire problem

Hi,

I have a 50 Buick with a 248 straight 8. I have a home made intake manifold set up for 6 Carbs and home made headers. I am currently only running 2 Carbs. The other 4 have solid gaskets under them and the fuel lines blanked off.

My problem is after a drive of 15 plus minutes it backfires extremely loud about 4-5 seconds after I shut down. If I start it back up within a couple of minutes for a short period of time and then shut it down again it will go off like a shot gun.

There is always a 4-5 second delay after I shutdown until it backfires. It does not do it every time. Probably about 50% of the time.

I am pretty sure my float levels are correct. Any suggestions would be apreciatted.

Bevan

 

Really......no one has any experience with this?


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This could be caused by a slightly rich mixture going off after shutdown by a hot spot on an exhaust valve or a glowing carbon deposit in an exhaust port. Will it idle slower?

 

Which two carbs?

 

It idles at about 700-800 rpm. So it could probably be slower.


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The second and fifth.


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Any other ideas guys.


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