LUVTruck.com

I walked outside this morning to head to work, fired up the LUV and BOOM! It sounded like someone fired a cannon off in my driveway. I popped the hood expecting to see a catastrophic mess, but everything looked fine. I got back in the trunk to see if it would start, it fired up fine, but was noticeably louder. Crawled under the truck to find this:


I drove it to work, and, despite being mind numbingly loud, seems to drive fine other than a noticeable drop in torque since I have no back pressure. The exhaust is about 3 months old, from the header back. The truck had been parked for roughly 12 hours overnight before I started it, and it popped on the first crank. Also, it rendered my fuel gauge inopperable for what ever reason....I'm guessing the concussion from the explosion knocked something loose.

Any idea what caused this and how I can prevent it from happening in the future? Anything I should check that may have been damaged in the explosion?

Thanks for your help guys!

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1978 Mikado *Weber 32/36*Offenhauser intake manifold*Pacesetter header*Custom exhaust*Pertronix Ignitor & Flamethrower 40,000v coil*

Someone put a potato in your tailpipe?

No french fries in the driveway, so I don't think so. It seems like the reasons this usually happens are A) clogged exhaust (not likely since the system is brand new) and B) gasoline pooling in the muffler due to a rich a/f mixture (Doesn't seem likely since the car was sitting for hours before hand, I would imagine the fuel would evaporate overnight)

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1978 Mikado *Weber 32/36*Offenhauser intake manifold*Pacesetter header*Custom exhaust*Pertronix Ignitor & Flamethrower 40,000v coil*

Depending on which way the pipes are turned, the evaporated fuel might not have had anywhere to go. If the fuel can't escape, it will become a vapor and it's possible it could have stayed in the muffler, where it ignited.

Good point. The exhaust does sort of angle down, and then back up so it might have gathered at the low point.

I got this response on another forum:



Now my points have been replaced with a Pertronix ignitor, my coil is a new Pertronix Flamethrower 40,000v, the wires are new, the cap is new, the rotor is new, the plugs are new...but the plugs were installed before I got the truck running so I'm 90% sure they're pretty sooty/fouled. Do you think fouled plugs might be enough to blow the muffler.

I just want to ensure this doesn't happen again, and I'm still new to carburetors...I've always had fuel injected cars in the past so this is all pretty new to me.

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1978 Mikado *Weber 32/36*Offenhauser intake manifold*Pacesetter header*Custom exhaust*Pertronix Ignitor & Flamethrower 40,000v coil*

Sorry, had to!

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Click on C.M. logo to go to my webpage


RIP R.J.B.

I'm not sure. Maybe someone else will chime in. Definitely check your mixture, choke, float level, and your timing. You could be too far advanced and have spark while your exhaust valve is open.

If carb leaks down, fuel can pool in the low spot, namely your muffler. Spark through exhaust and poof...

Regardless, the muffler was restrictive enough that the explosion split the seam, as it had no where to go...

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If you think no one cares, try missing a couple of payments...



FIAA!

SFPP!

I got a muffler you can have if you'll cover shipping. It's aftermarket. Cheap.

It was a generic turbo muffler. I'm not really happy with the exhaust anyway, I'd like to move it above the cross-members for clearance, and I want to throw a glasspack in before the muffler since the old set up was a little tinny and overall louder than I'd prefer. It was a hasty job to pass inspection, so I'm not all that sad to see it go.


Thanks for the offer, I really appreciate it. Luckily, I have a couple of mufflers in my parts pile so I can get this taken care of...I just don't want to have to come knocking because I blew out the new mufflers too.

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1978 Mikado *Weber 32/36*Offenhauser intake manifold*Pacesetter header*Custom exhaust*Pertronix Ignitor & Flamethrower 40,000v coil*

Here's what I suspect happened; you get in a cold truck, pump the accelerator maybe a couple of times & start it, maybe with partial throttle. The Weber gives it a good squirt of fuel with every pump, maybe you give it a bit more throttle than normal, maybe the fuel pressure is a bit high, maybe the carb is just a bit rich, any or all causes a very fuel-rich charge into the engine, so rich that not all of it burns and a part of this fuel-rich mixture is forced into the header, then the exhaust pipe to the muffler. Because of the efficient scavenging of the header (& maybe because the timing is a bit advanced to maximize the carb & header) a spark or glowing piece of carbon accompanies the mixture down the exhaust pipe. Nothing happens until the mixture & spark get to the muffler, which just happens to be a large volume of the third thing required to support combustion- AIR!- & ignition of the now-perfect mixture occurs. The tailpipe is not large enough to vent this sudden huge volume of expanding gasses, the pressure from the running engine prevents escape that direction, pressure rapidly builds to the point the cheapo muffler seam fails with a loud "boom". It may or may not ever happen again.
OR it could be something like the residual pressure in the fuel lines is causing the carb to leak down. If this is the case I don't see how all the fuel is going through into the exhaust, most should bypass the rings into the crankcase. Sniff the dipstick for gasoline smell after the truck has been sitting as before. If you smell fuel in the oil you need to fix the problem quickly before you ruin an engine.

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'78 Chevy LUV,1.9,4sp,headers,31's,SAS Dana 30,Dana 20,SOA rear w/Aussie Locker, rough body, bought new 12/4/78.
'87 Trooper,2.3,5sp,headers,31's,ball joint flip & spacer,Aussie Locker rear,Superwinch hubs,brush guard w/5.5K winch,more to come.

To get that much fuel in there to get that big of explosion I thing more is going on here. Make sure your fuel pump is shuting down with the key off.

Does the weber utilize the return line? Either way, it wouldn't hurt to make sure that the needle and seat is clean. A little speck of trash in there can cause the carb to overfill.

Had the same thing happen to me.....However, I was the cause by somehow inadvertantly turning off the ignition during a drive and realizing so, I turned the key back on after a coupla seconds and WHAM. Got out and saw the same damage. Had to get a new muffler for the LUV. Sounds like your muffler was a result of a carburetor leak, like the others are saying, since it happened overnight. And Egg says check the fuel pump. He's right. My pump is rewired to the ignition switch and guess I did it 'not quite correct' because it also comes on in the acc. position. Occaisionally I turn the key too far and leave the pump running while I'm getting out but usually I hear it and go back to shut it off. Maybe someone wired yours 'crooked' too.

The dipstick doesn't smell like gasoline luckily. No return line on the Weber, I'm using a Holly fpr. Today the gauge on the fpr was reading 0. I noticed a bit of fuel pooled up on top of my intake manifold near the water neck. Probably leaking from the front of the carb.... I took it for a drive it didn't have the stuttering problem it had the last time the gauge read 0 (when my fuel pump was dying). I tightened the carb down a bit, leaned out the a/f mixture a little, checked the timing (8 deg), put in new plugs and new wires. I went to work, came back, and clicked the fuel pump on, gauge reads the normal 3 psi. No gasoline was pooled up on the manifold, but I'm going to check it again tomorrow. My fuel pump comes on with the key in the on position, it stays off when the truck is switched to acc.

If I had to guess where the fuel was leaking from it's likely here:

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1978 Mikado *Weber 32/36*Offenhauser intake manifold*Pacesetter header*Custom exhaust*Pertronix Ignitor & Flamethrower 40,000v coil*