1970 Deville Carburetor

[Jvteach07]

So after some very rough,  starts and ANOTHER exploded muffler I realized it need to replace the carburetor (car sat for about 15 years). Looking at the label on the side there is a label Rochester Quadrajet and the numbers on top 32747 and 32712. Should I have this re-built or replaced and where should I look online? And finally what should I expect to pay for this?

[dochawk]

When I needed one (my 72 had a 75 carb with an extra vacuum line terminated with a screw . . .), I was able to find ACDelco factory rebuilds on eBay for $200-$250.

For that matter, rebuilding the first one from a kit was fairly easy.

There seem to be two or three part numbers for the carb for any given year, but AFAIK, they are identical.

[Big Fins]

If the carb is original to the engine, always rebuild that and use it. You have no idea what you are buying off of the shelf these days

[Bob Hoffmann CLC#96]

I think your problem is sticking valves or jumped timing.
Bob

[fishnjim]

'70 Rochester Q-jet numbers should begin with "704xxxx".   
Might be looking at the wrong number or the tag is missing.    Just a guess, raw gas getting down the exhaust, the float(s) maybe corroded/pin holed.   Hard to start when too rich.   Once it burns off a bit then they start, but stall and your'e back to zero.   
I'd take the top off first and look in there and see if it's junked up or corroded, any obvious issues.   
I don't like/recommend starting cars that sit without prepping them first.   This is what you get into, it don't run right then you're scrambling to figure it out.   If you go through each system, fuel, ignition, oiling, electrical, etc and make sure they work first, they when all working, it'll run.

[35-709]

In my half-vast experience, the cause of an exploded muffler is usually intermittent ignition or as Bob Hoffman suggested.   Even a brief moment of interrupted ignition will allow unburned gas from one or more cylinders to be pushed out of the cylinder and into the exhaust system and the next time a cylinder fires the hot exhaust will ignite the unburned gas and blow the muffler apart.  After 15 years of sitting your Q-Jet may indeed need a good internal cleaning and rebuild, but I would be looking at the ignition side of things for the cause of the muffler exploding.

[dochawk]

The one time (depending upon how you count) that I had a muffler detonate:

I was driving an Impala 400, and we were heading to a movie outside the normal territory we roamed.

A couple of days earlier, some routine work had been done on my car.  By a mechanic who was generally good, but had a pattern of hiring kids that *weren't* up to snuff.

So pulling onto the freeway, I gunned the engine (San Jose traffic, not much choice quite often) . . . and at full throttle, the car suddenly sagged, and dimmed, and *WHAMMMM!* . . . at which point it was loud.

And then when we suddenly found our offramp, and had (again, Bay Area traffic) to brake hard, and again the lag, dim lights, and  *WHAMMM*.

It turned out that they'd left a hot,+12V, wire dangling.  So both acceleration and deceleration meant that it continued inertially, while the rest of the car accelerated or slowed, and it contacted ground, shorting out spark, leading fun throttle fuel flow to detonate int the muffler.

So the first time, it blew 13" of tail pipe clean off, and the second, new the muffler  apart at the seam, and spun it 30 degrees on the axis.

Result:  loud, smelly car . . .

And shortly thereafter, before it was fixed,  I was in San Diego.  I gunned it for a steep hill, just to hold speed, and at the light . . . A man got out of the ambulance behind me, walked up to my window, and asked, "Sir, did you know that your car is on fire?"

Excuse me???

"Don't worry, it's just a small fire."



We pulled over, and here was soot on the bumper--right above where the tailpipe would be.   It *should* have backfired from the excessive fuel, but there was nothing to contain the explosion, so it just flowed out of the stub of the tailpipe.