Webers with exhaust poping badly

[Eljaro]

I have had my 48IDA webers (on a 427 CO with Dove F5 head s and Comp Cam 282S solid lifter cam, 236º duration) now running for a while, and after changing the emulsion tube to a F5 the transition hole got the fix.
I still have the problem with the loud exhaust poping, including flames shooting out of the sidepipes. It was fun for a while, but it is definitely too loud and it will brake the innards of the sidepipes eventually.
I have removed the sidepipes twice and renewed the header gasket and sealed the header tubes which slip into the sidepipes with a special exhaust paste, which seems to have sealed the pipes, since there is no residual sooth now around where the pipes and header pipes meet.
But I can not get rid of the poping, which only happens when getting off the gas, when only the idle circuit is functional and the throtle plates closed.
Any hint as to what can cause this ? How can I check if there is still an exhaust leak?
Jetting is 160 main, 200 air, idel 60 and holder 120, pump bleed 50 and emulsion tube F5.

[Allan A]

Eljaro,

I have the same problem, it is driving me nuts. Hoping to get it fixed soon. Here is what I have on a 347.

- Comp Solid Camshaft 31-000-5 302 firing order 2500/6800RPM 244/252
@050 555/563 INT/EXH 1.6 Rockers 110 Lobe Seperation Lobe# 6057 I 6089
E

- Edelbrock 7717 Victor JR Race Cylinder Head Set W/Ferrea Valves

- Venturi 37
- Main Jet 150
- Emusion Tube F3
- Air Corrector Jet 160
- Emusion Tube Holder
- Idle Jet 55 F10
- Idle Jet Holder 120

[jay bentley]

I had the same problem on my cobra when I bought it. Turns out it was all fuel pressure related. In my case it was a lean condition which made it pop under deaceleration. After the fuel pressure was adjusted its been fine. The popping and flames absolutely drove me nuts!!

Jay

[dsmith]

Check those header to head gaskets again. Not going to tell you that this is the answer, but I had the exact same symptoms with my 428 and cured the entire situation, flames and all, with the header gasket change.
I couldn't find a good set of header gaskets without the bolt holes on the side until I spoke with Bob at ERA. Was able to get a solid set.
After instillation, no backfire - no flames

I do kinda miss those flames from time to time....

[Eljaro]

I removed the exhaust for the third time now, and will have some exhaust gasket made to size with only the vertical holes. Hi temp silicone will go where the header pipes slip into the sidepipes. Will see if I finally get that popping sorted out.
I have read that the popping is actually a sign that the carburation is spot on and that it will not harm the engine nor the exhaust. Only the neighbours.

[Eljaro]

I did take both exhaust systems off again and back on, sealing the slip on sidepipes to headerpipes with a special exhaust silicone sealant. I also made myself new special exhaust gaskets with only the vertical holes. All tightened up and no leaks as far as I can see.
But the backfiring on deceleration just does not go away. Whenever the throtle plates go shut backfiring occurs. The only way to get it reduced is if I set the idle say at 1300 rpm instead of 700-800.
I think I have jetting problem here, because it backfires from both sides no matter what.
The timing ist set 20º at idle, 38º max advance.
I also consistently find a pool of gasoline inside the carb throats several minutes after stopping the engine when it has run hot.
Help needed here before I start to tear everything down. It is a pitty, because otherwise the engine runs incredibly good. But the backfiring makes me go crazy.
Could it be a leak somewhere between the carbs and the intake? Or between the intake and the heads ? Or too rich an idle mixture ? I really do not know what is going on any more.
HEEEELP !!!!!!!!!!!

[Allan A]

We just fixed 95% of my backfiring, the MSD was missing a spring. The new timing is about the same as yours, it feels like about 50 more HP. I still might have one fouled plug on the driver side, will replace the plugs and see how it runs. Good luck.

Allan