Engine back firing?

[MFE III]

What can cause back firing through the exhaust on throttle lift off?
I get a nice loud pop between shifts if I'm on on it a bit and on deacel it's a steady series of pops on both sides. I've got slip-fit header to sidepipe connectors, so I know I have some exhaust leakage. I know that cool air getting sucked into the exhaust can cause it but wondering if there were other things I should check. Checked the timing and it's fine.
Thanks
Matt

[Bannon]

I would check header to cylinder head fit. Mine had a backfire issue before I bought it. former owner took it to a shop and they machined the header flange and no more issues.

[patrickt]

Yep, leaky primary pipe connections at the head will cause that sort of popping -- that's the first thing I'd look for.

[bobcowan]

After that, check the mixture. If it's lean it will also do that.

[elmariachi]

Matt, its likely the slip-fits. Mine did this crap for a year before I said F-it and got the flanges from Steve. Check the other items mentioned but I suspect its the pipes.

Jim


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[chomama1]

Mine does this too, I thought is was normal. So, consensus is it's the header flanges do not fit flat up against the block? Or timing or too lean? Not sure who Steve is or how flanges would work. Are we talking about exhaust leak at the header gasket?? Is this a gasket problem or a metal problem?

[Danr55]

If you car is carbureted? (naturally asprirated) check the power valve in your carb. If you blow a power valve it can do that.

[chomama1]

No, it is stock Ford fuel injection. I hate the look, but it does start and run good.

[elmariachi]

Originally Posted by chomama1

Mine does this too, I thought is was normal. So, consensus is it's the header flanges do not fit flat up against the block? Or timing or too lean? Not sure who Steve is or how flanges would work. Are we talking about exhaust leak at the header gasket?? Is this a gasket problem or a metal problem?

The consensus is its an extreme lean condition caused by an exhaust leak, either at the headers or in the case of some of our Hurricanes, leaks at the slip-fits. If its at the header face, it could be the header flange or the gasket, depends on the car and condition.

Steve is Steve Sinnard, GM at Hurricane and the guy that supplies the flanges to convert Hurricane slip-fits to flanged setups. That requires you to be using their side pipes and cutting and welding the flanges into place on both the header and side pipe.

Regardless of the cause, backfiring or popping out the exhaust is not normal.

[mpanten]

Get some remflex gaskets, If its fi and you havent changed anything thats probably what it is. Mine was backfireing beacuse it was to rich but either a lean or rich condition can cause it.

[madmaxx]

Had same thing it was the slip fit side pipes, once sealed the backfire stopped

[jmimac351]

Originally Posted by mpanten

Get some remflex gaskets, If its fi and you havent changed anything thats probably what it is. Mine was backfireing beacuse it was to rich but either a lean or rich condition can cause it.

Agreed about using Remflex gaskets. I had a header flange that was not true and nothing seemed to fix it. I fixed it "a little" with regular FelPro but they eventually blew out again. I even tried copper gaskets and they were worse.The Remflex took up the slop and it was never an issue again. They are made of sliver thin layers of graphite and compress, take up the extra space, and supposedly provide a little spring load which helps the header bolts stay tight. HIGHLY recommended. And the heat rating means they won't burn / blow out. But you already know that...