Just bought a Qjet from a late 1977 Chevy.
It has a bi-metal choke that looks a lot like an electric choke, except there is no wire to hook it up. It has a vacuum port instead. What do I plug this port into?

And in the place of the mixture control solenoid, it has what looks like a fifth jet/metering rod controlled by a brass accordion. What is this thing for and what, if anything, does it need to be connected to?
Thanks,
Homer

 

Yuck.

Probably one of the most anti-performance carbs possible.

THe choke is a "hot air" type. It uses a little tube that hooks up to that fitting and then there's a little coil of steel tubing that is down in the exhaust passage in the intake. The other end of that comes up and hooks to a port on the back of the carb at the very top. The thermostat housing has a small vacuum feed, so the engine draws air into there from the heat coil, and clean air from the back of the carb comes in to replace it after it's been through the tube and gotten hot. Pretty hard to graunch onto an inatke not set up for it. It might be possible to replace the thermostat with an electric one, but I don't know, it has never occurred to me to bother messing with a late 70s Q-Jet for a performance application.

The other thing is an "aneroid". It provides altitude correction. It makes it leaner as the ambient pressure goes down. It doesn't "connect" to anything.

 

Homer, you are in deep ka-ka, man. You've got what I call a "super emissions" QJet. That thing has more tweaks and gee-gaws than a little bit. I bet you also have a weird looking 3rd jet and rod jsut in front of and to the passenger side of the 2 primary rods/jets, right? And probably some other wierdness that you won't find in a more common QJet.

The brass accordion thing that has it's own rod and jet below it is an "altitude aneroid" that compensates for altitude changes by slightly richening/leaning the mix. If you decide to remove it and plug it's jet you need to go up about 6-8 jet sizes on the primaries to compensate. Your stock primary jets are probably around a #60, right?

The choke you've got is a hot air style choke. It's supposed to draw air from the back of the carb up on top (there's a vacuum fitting there) and then down THROUGH a special bolt-on fitting with tubes that stick down inside the exhaust crossover in the intake manifold to heat the air and then finally to the little fitting that sticks out the front of the choke housing. This is a MESS to try to make work on anything other than a stock factory QJet intake or an Edlebrock Performer. AND you need all the special lines and fittings. In short- forget it. Convert it to an electric style choke, plug the vacuum fitting on the front of the choke housing and be done with it.

If you've got the strange 3rd jet and rod in front of and to the passenger side of the 2 main primary units you can remove/plug them as well, but you'll have to jet up the primaries another 6-8 jets sizes to compensate. Removal involves plugging the 3rd jet and removing it's metering rod, but leaving the power piston it used to be connected to in place to prevent a horrendous vacuum leak.

This is a LOT of work for a junkyard carb. If at all possible, sell it to someone else and buy a Qjet that's simpler and easier to tune.

 

Now they tell me...No wonder this thing was so cheap. I'm starting to realize why everyone just buys EFI.

I like the idea of a hot air choke. It seems to be a more relevant way of choking an engine than electric. But that sounds too complicated, so I'll go with the electric. It will probably just bolt right up.

So this accordion thing richens the mixture somewhat depending on ambient pressure? And if I plug it up, I can re-jet and pretend it's a normal q-jet? That doesn't seem so bad.

Where's a good place to get primary jets/rods? Do I have to buy some huge kit from edelbrock that'll probably cost fifty bucks?

What controls my primary rods? How do I make sure that's set up right?

Thanks,
Homer

 

Throw that thing away. Cut your losses (which I hope are less than $5 or so) and get a better core to start out with.

You can polish a turd from now till doomsday; and at the end of all that polishing, it'll still be a turd. Basically, that's what you've got. Don't waste any time or money on it because it will never turn into a performance carb.

 

Ok. So be it.

Where's a good place to get a carb? Seriously, the junkyards around here have squat.

 

What's the application?

 

1988 Caprice 350 "LM1"
~180 Hp
8.2 CR
CCC Quadrajet (converting to non-CC)
700r4
3.08 positraction 8.5" 10 bolt

 

So what year range of quadrajets should I be looking at? Does it have to be pre-1970?

Is a 70's carb okay as long as it doesn't have that accordion jet/rod?

RB, where do you find a $5 carb? I'd really like to know.
Thanks

 

Nobody has any input?

 

The best all-around Q-Jet core for most purposes is 7029202. 69 350.

I would not use any carb that has a prefix of 704 or 170 anything. They are all emissions-crippled. But that's just me. To paraphrase a stupid commercial, I have very simple taste in carbs, I only want the best, and will use nothing less.

Swap meets is the place to go for cheap stock stuff. You can find the most amazing things there sometimes.