Muffler exploded plus sweet backfiring problem 1975 2F (1 Viewer)

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Joined
Aug 2, 2014
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Location
Watertown, NY
Today I was driving back to work from lunch and heard a weird noise like squeaking of brakes, but I wasn't breaking. This was shortly followed by a very loud bang (backfire) and I immediately pulled over. The engine was still running just fine and when I let off the clutch it had power but now my exhaust was much louder. I upshifted into third gear and provided a little more gas and the engine suddenly lost power and then it was followed by another very loud backfire. Again the engine was still running fine and I was able to continue driving it to my work which was only about another 1/4 mile away. As I pulled into the parking lot and revved the motor a bit to test, it again lost power and backfired loudly. Shut down the truck and looked underneath and my muffler was wasted. Blown apart at the front seam. So before I took off for home I did some carb adjustments to see if I could stop it from doing this. It seemed to work okay, but it did do it one more time again on the way home and that was even with me babying the throttle and never getting the rpms very high. Anybody have any idea what might cause this? exhaust manifold leak, worn cam lobes, lifters, carb? I don't want to get a new muffler put on only to find that it explodes again.:bang:

Here is what I am running
1975 2F desmogged
Weber 32/36 rebuilt about a year ago (yes I know it is not the best carb for this motor, but it was running just fine)
JT Outfitters header
Pertronix in the dizzy
Just replaced the coil a week ago
Just replaced the plugs a week ago

Like I said it was running great and then it suddenly exploded the muffler and keeps on backfiring.
 
Hi, check timing and probably running too rich. Mike
 
My guess is that your ignition is intermittently cutting out.
The engine makes a few revolutions without getting a spark, pumping fuel + air mixture into your exhaust system.
Ignition resumes and sets it off.

I'd look for a loose wire, something shorting to ground (condenser) or a failing electronic ignition module.
Given that you just replaced the coil, you might want to look around there first.

Good luck
 
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Thanks guys I am going to check those today. I will look for any loose connections then set timing. I will update later.
 
Also inspect plug wires and connections. An intermittent plug wire will cause these symptoms.

My shop dog is still traumatized from my muffler exploding. :)
 
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your dizzy probably came loose or grenaded inside. i blew my muffler up when i was learning how to set timing. it was way advanced and the muffler blew apart at the seams.
 

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