So our newly rebuilt 235 is a great thing. Turns a lot of heads. Runs great! But as of yesterday it seems to be sucking air back up the Holley 390 carb when you let off the gas pedal. Is this indicative of an exhaust leak somewhere?
Thanks,
Fabian.

i don't quite get the problem. could you explain it better? is it back firing?

No, it's not really back firing. It is more like a flutter you can hear in the carb when you let off the gas. Its not a pop or pow!
Thanks,
Fabian.

By the way it is a rebuilt60 Chevy 235. Just hit 500 miles. 20 over pistons Hi Po Solid lift cam from Patricks, Clifford Headers and water heated Intake. Holley 390 Carb. Langdons Mini HEI ignition.

Dear Fabian;

Are you sure this isn't just an exhaust "rumble" as headers will do that??

Put a vacum gauge on it.also Use some soapy water on near & around any mating surface of the exhaust.To check for any type of leaks.

Thanks for the advice.
It was an exhaust leak.
The motor was sucking up air when we let off the gas.
The header flange is thinnner than the intake flange on Clifford products. I had to really crank down on the washers and bend them pretty good to seal it up at the head.
Fabian

Be careful about cranking the bolts down - you don't want to crack something. You might consider milling the high spots so everything is level so the washers pull evenly

I had the same problem with my Clifford intake and header's. I installed studs, and then used larger brass washers under the nuts and lock washers, worked great!!.

Dan,
That sounds like a great idea. I suspect my bolts worked loose a little. Plus the weight of the exhaust system on the headers is actually making them flex. I plan on adding some hangers right past the firewall to support the weight of the pipes ahead of the mufflers.
Fabian

Attach the front tailpipe hangers to the bellhousing rather than the frame so that they rock with the engine.

I never had any problems with offey intake & clifford headers, Clifford intake & clifford headers. MY intake clifford headers/Cut and redesiged to mine.. The Issue is that when a engine goes through it's heat cycle Things NEED to be retorked. I run studs and the stock Clamps with a lock washer on all.
On all my Intake & Headers settups.Once the motor goes throught a heat cycle Or two I retork each time. No problems there AFTER.Useing a MrGasket 155 in/ex gasket with a Skim coat of Copper RTV
I also use a Skim coat of the coper RTV on my collecter gasket as well and NEVER had any problems.

I haven't tried the copper RTV yet, but I really like the (K&W?) spay-on coppercoat, I even use it on head gaskets.

Yeah - well ther in lies my mistake. I installed them dry.
Fabian.