Pop goes the muffler

[Imndeep]

Hola!
I've been having the strangest issues with my Road Runner lately. What’s going on is that after she warms up the Engine dies. You go to start it up and it just spins. So then like an idiot I load the intake up with fuel giving it a couple of pumps and holding the pedal to the floor until I get ignition. Sometime that works sometimes not. I decided last night to go grab some fresh fuel for my girl and drove her for the first time other than laps around my neighborhood. It was great, the 4 speed I just installed worked great, a little stiff, but good. A lot of gear whine being I have a 489 cased Dana power lok with 4.89 gears. The gas station is only a few miles down the road so I went for it. I made it to the gas station filled up with premium then tried to start her up to go home. She started up but stumbled and died. So here I go again, pumping the throttle and holding. Well, when the engine finally caught a HUGE backfire ensued, man the thing sounded like a 12 gauge going off, scared the $h*t out of the lady behind me! Well, that was enough to get her going again, so I made the mad dash to get home before it died again. I made it home, barely. When I was backing into the garage it died again and wouldn’t start. This time I just let it sit. After a half hour it started right up and I managed to position her in the garage. My Ford buddy seems to think it’s a coil issue. I’ve changed out distributors, changed plugs and messed with my timing til the cows come home. Timing set at 0 degrees being she’s a 4 speed car. Title of the Story is pop goes the Muffler, well, the Passenger side muffler was the casualty of the massive back fire, it deformed and split. I just put the damn pipes back on to drive it to the gas station too.
So what do you fine people believe the issue is from that brief description?

 

[mrsnicks]

You didn't say if electronic ignition or points. I had a similar issue and it ended up being the condensor was bad. Sometimes it would start, sometimes it would stumble, sometimes I couldn't get it to start no matter what I did.

Patrick

 

[Cranky]

You might try and advance your timing a bit and see if that might help some. Just because it's a stick doesn't mean 0 is the place to be. All engines are different and today's gas isn't like what it was back in the day when the book said to use the timing listed. Besides, I've never gone by the book and my cars run well by giving them what they like. And on the gear whine.....how loud is it? Just because you have deep gears doesn't mean it's ok for them to be noisy.

 

[bigmanjbmopar]

Sounds like heat soak to me, today's gas evaporates fast so you need to isolate the carb from the intake with a spacer or heat absorbing gasket.

 

[Imndeep]

You didn't say if electronic ignition or points. I had a similar issue and it ended up being the condensor was bad. Sometimes it would start, sometimes it would stumble, sometimes I couldn't get it to start no matter what I did.

Patrick

Sorry, I meant too. Current Ignition system is NGK plugs, Moroso 8.5 mm wires, Factory Vacuum advance distributor, Accel Super Coil, Mopar Performance (MSD) Box.

- - - Updated - - -

You might try and advance your timing a bit and see if that might help some. Just because it's a stick doesn't mean 0 is the place to be. All engines are different and today's gas isn't like what it was back in the day when the book said to use the timing listed. Besides, I've never gone by the book and my cars run well by giving them what they like. And on the gear whine.....how loud is it? Just because you have deep gears doesn't mean it's ok for them to be noisy.

I picked up the rearend about 12 years ago off of eBay, I wanted a 489 cased Power Lok, cause at that time I thought that's what 1968 Road Runners came with instead of the 742 cased Auburn type limited slip. It's seems I was a bit confused on that matter. MyMopar states that a 742 case was from '61
to '69 and that the Power Lok was from '58 to '69. So I need to take my Power lok out of my 489 case and put it into my 742 case! LOL I'll do that when I buy more reasonable gears 4:89 is ridiculous! I'm in 4th at 50 mph at 2500 RPM

Sounds like heat soak to me, today's gas evaporates fast so you need to isolate the carb from the intake with a spacer or heat absorbing gasket.

Didn't even think of that, My Manifold is an Edelbrock Torker, which has a huge air gap.

 

[bigmanjbmopar]

Sounds silly but try insulating your fuel lines especially the ones near the block to carb. use a phenolic spacer under the carb. aluminum is the best heat transfer right up into your carb bowls! lol

 

[Daves69]

How are your plugs reading?

I think I'd check the ignition run circuit including the ignition switch. You might have an intermittent problem or loose connection. Maybe even an internally corroded wire.
Why I mention that is your backfire in the muffler reminded me of this............
Back in HS days some friends/jokers would be driving their car by where your walking, turn the ignition off while staying on the gas, let it coast for a bit, let off the gas then turn the ignition back on to make it backfire out the exhaust trying to scare ya. And yes, it can open the muffler up.

 

[mopar 3 B]

What carb are you using?

 

[Imndeep]

What carb are you using?

Edelbrock 1413, 800cfm carb.

 

[Bigal75]

Did I read 0 degrees of timing ? If indeed that's the case well there's your problem.

 

[ArtH]

Did I read 0 degrees of timing ? If indeed that's the case well there's your problem.

I agree. That seems a bit retarded which would be throwing unburned fuel mixture into the exhaust system. That would cause a back fire, kind of like turning off the ignition while cruising and then turning it back on. You can blow the heck out of a muffler that way...do you hear the voice of experience there?

Advance your timing to about 10 degrees before top dead center and see what happens.

 

[Imndeep]

I agree. That seems a bit retarded which would be throwing unburned fuel mixture into the exhaust system. That would cause a back fire, kind of like turning off the ignition while cruising and then turning it back on. You can blow the heck out of a muffler that way...do you hear the voice of experience there?

Advance your timing to about 10 degrees before top dead center and see what happens.

I'll give it a shot, can't hurt right?

 

[ArtH]

I'll give it a shot, can't hurt right?

Not at all. 10 degrees BTDC is about factory spec for most engines of that period. Make sure the vacuum advance is removed from the distributor and plugged...a golf tee is great for that. If the car is hard starting then it's possibly advanced too much, back off a few degrees.

 

[petieg383]

Edelbrock 1413, 800cfm carb.

You absolutely need a spacer for an Edelbrock carb. Today's fuel will be boiling right inside an Edelbrock carb because of where the bowls are. After heating the car up and shutting it down you'll be able to hear it bubbling inside the carb. Ask me how I know...

They sell a 3/8" spacer made for that carb that helps pretty much eliminate the fuel boiling issue. Try one if you're sticking with that carb.

And yes fix your timing.

 

[70beeper]

Not completely on same subject, That backfiring is like the old Hall-Scott gasoline truck engines from the 50's & 60's (1091 CID) They always backfired from the unburned fuel vapor in the hot exhaust system.

 

[Imndeep]

This forum is awesome! I want to thank everyone for their ideas. My timing was WAY off. I set it with the vacuum port closed of course. Set it at 10 degrees advanced.She fires right up and no stalling from boiling fuel. I will get a spacer as everyone is suggesting, not a bad idea. I like Carter Carbs, and basically, that's what an Edelbrock is. She's a happy 383 now. Thanks everyone once again.

 

[MarPar]

This forum is awesome! I want to thank everyone for their ideas. My timing was WAY off. I set it with the vacuum port closed of course. Set it at 10 degrees advanced.She fires right up and no stalling from boiling fuel. I will get a spacer as everyone is suggesting, not a bad idea. I like Carter Carbs, and basically, that's what an Edelbrock is. She's a happy 383 now. Thanks everyone once again.

indeed!! :hello2:

another satisfied customer! lol

 

[bee71]

Same thing happened to me. Blew the passenger side muffler all to hell. Turned out to be a bad coil.

 

[Imndeep]

Same thing happened to me. Blew the passenger side muffler all to hell. Turned out to be a bad coil.

That's the way I was originally leaning, bad coil. Good thing I didn't replace it, although it's a 20 year old Accel Super Coil. I should upgrade eventually, but if it aint broke, don't fix it ;)