muffler explosion

[gregchrysler]

Hello  again   I was running my 251 ci spitfire for about 5 minutes and giving it gas and I thought an ied was under my car.  It actually blew the muffler apart

I know the gas isn't getting burned but is it the carb or the plugs fouling or float or timing?  ANy ideas  Thanks

[joe_padavano]

Muffler explosions can only be caused by excess fuel pooling in the muffler. There are a myriad of possible causes, from an overly rich carb to an improper float level to a misfiring cylinder, and on and on.

[Rusty_OToole]

Was there black smoke coming out the tail pipe? If you were running rich you would see black smoke.

 

MUCH more likely to be a misfire in the ignition system. But, it is practically impossible to get that much gas into the muffler. We used to shut off the ignition for a few seconds going down hill and turn the key back on to make a backfire but you really had to be asking for it to blow a muffler apart. In other words the ignition would have to stop working for 5 or 10 seconds at a time.

 

Would suggest you flooded it badly on starting but if you did that, I doubt the plugs would fire at all.

 

You DO NOT get a backfire like that for no reason. Either you did something, or the engine did something, and it had to be fairly radical. If you say "the muffler just blew up, suddenly, for no reason at all" either you are bullshitting (like we used to do when dad asked what happened to the muffler) or something happened that you failed to tell us about, or failed to notice.

 

As Joe said the only cause of such an explosion is too much gas pooled in the muffler and that gas didn't get there by itself.

Edited April 1, 2018 by Rusty_OToole (see edit history)

[Digger914]

constant velocity side draft carb could be way out of adjustment or the needle could be bent, or its so sticky its not letting the pot drop.

[dei]

Not the same thing possibly but...

 

Dad had a 1959 Oldsmobile 98 when I about 13 and we were coming home using back roads when I asked him if the now older Olds still had top end power?

That car cruised 65 not missing a beat and without answering me he punched the pedal to the floor and off we went!

I watched the colour changing speedometer go from orange to red as we hit 70 quickly and then 80 and... Suddenly there was a loud BANG and the rumble from the exhaust was incredible to me!!

Scared and being a kid I said I was sorry (for what not sure) but he started to laugh and said don't worry about it.

As it was summer and no central air Mom heard us come home and Dad had some "splainin' to do".

 

The thing was this, he had to have a new muffler and tail pipe put on three weeks earlier so went to Midas Muffler to have what was then advertised as "Life Time Warranty". 

He went back to that shop with his three week old blown out muffler (which they replaced free) and soon learned they had put a smaller muffler than factory on and the tailpipe was a quarter inch smaller in diameter. Suspecting the increased back pressure putting his foot into it did not help and fuel accumulated then BOOM!

 

Oh, and Dad learned that "free lifetime muffler replacement" was correct but... the labour was not!

He never went back again...

Edited April 2, 2018 by dei (see edit history)

[gregchrysler]

Rusty  there was black smoke coming out exhaust   = also not much power  i had to gun it to get it to move forward and that is why I think it got too much gas   what about a cylinder misfiring?  thanks for replies how much vacuum should there be on carb?  thanks 

 

[Owen_Dyneto]

A friend had that happen to him with a just prewar Packard.  Cause was a very sloppy-fitting distributor rotor (missing the little metal clip that assures a snug fit).

[gregchrysler]

thanks owen   going to check each spark plug for fire   could the advance cause the problem or the timing   seems to run fine tho  but not much power  and i have 125 psi compression each cylinder

[Matt Harwood]

Is your distributor correctly installed? Some cars can start and run (albeit poorly) with the distributor 180 degrees off. That could certainly explain one dead cylinder pumping fuel downstream and one good cylinder lighting it off.

[Rusty_OToole]

If it came on suddenly could be a stuck float or a bit of dirt in the needle valve flooding the carb. Could also be a faulty float that has sprung a leak or got waterlogged with gas. Something needs attention, could be time for a tuneup including carb overhaul.

[gregchrysler]

rebuilt carb  new from California carb $400.00 6 months old

[gregchrysler]

if vacuum leak  could it  cause more gas in carb and not burn?

[Larry Schramm]

On ‎4‎/‎2‎/‎2018 at 12:59 PM, gregchrysler said:

if vacuum leak  could it  cause more gas in carb and not burn?

 

Vacuum leak would result in a leaner mixture.

[pont35cpe]

I had a `76 Lincoln that did the same thing, wound up being the molded end of the ignition wire to the coil. It would run fine, then was like the key was turned off, then back on, "BOOM" blown muffler..

[Ltc4748]

Hello Greg. I know you have been having issues with your car running correctly for a while. One thing to check that is often overlooked is the ignition coil, specifically the primary side wiring (small low - voltage wiring). If the ground side of the battery is positive polarity then the small wire that comes off the coil going to the distributor/points should be on the side of the coil with a + or something to indicate the polarity. if the battery has been hooked up with a negative ground then the coil primary lead going to the distributor/points must be connected to the - side on the coil. Years ago I hooked one up incorrectly and the engine runs anything but correctly. Changing the ignition timing out of specification makes them run better but not even close to decent. Take a look at the coil polarity and get back to us, Best of luck to you. 

Larry

[Bleach]

I vote for timing being off. When we were teenagers, my cousin would mess with the timing on his truck just enough to get a backfire when he'd let off the gas while driving. He'd drive around looking for unsuspecting pedestrians to scare, especially going through underpasses.  BOOM!

[gregchrysler]

I think it was from  running off the choke- no air getting in   choke was shut while running for a while  thanks everybody

[hchris]

Yep, choke closed would do it. Over rich mixture (black exhaust smoke) is a good indicator, as already mentioned unburnt fuel in the muffler probably ignited with hot carbon deposits.

 

Ignition timing (retarded) would have to be so far off that the engine would probably not run at all.

 

Another possibility is a burnt exhaust valve, not seating properly could cause exhaust (still burning) gases into a fuel soaked muffler with the same result.

Edited April 13, 2018 by hchris
spelling (see edit history)