Q-jet Base plate's
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Thread Starter
Team Owner
Joined: Sep 2003
Posts: 88,393
Likes: 2
From: eville in
Originally Posted by ksbunting
Lars would be the only one I would feel totally comfortable with as regards the answers to this question since he is the expert.
still have a few to tare apart
Melting Slicks
Joined: Mar 2005
Posts: 2,838
Likes: 10
From: Austin TX
The base plates are similar from 70-74. I believe all these have the brake booster nipple in the rear, unlike previous years. It's easily plugged with a threaded plug if you wish.
Stay away from 68-69 base plates. In these years, exhaust gas was routed through the intake to heat the carb for warm up and reduced emissions. A thin "heat shield" was sandwiched between two gaskets, but it was bad design...in fact Chevy had several service bulletins and maybe even a recall in 69. Turns out 8-900 degree heat isn't good parts made of pot metal (though the base is alum). Regardless, there are a lot of 'service' carbs with 68-69 dates out there.
I've heard to stay away from Carter-built Q-Jets, but I've never read anything credible that defends this theory.
Lastly,..you want nothing to do with smogger Q-Jets (1975+). These are stamped "7045XXX" or higher numerically. The range of tune is lost, even on the idle mixture screws which are in the base plates.
Good base plates are easier to find than good choke horns, which are the softer metal, and have suffered years of over-tightening which causes them to "bow" in the front which leads to metering and vacuum probs.
You might pick up the book "Rochester Carburtors" by Doug Roe...great guide!
Good luck,
Wes
Stay away from 68-69 base plates. In these years, exhaust gas was routed through the intake to heat the carb for warm up and reduced emissions. A thin "heat shield" was sandwiched between two gaskets, but it was bad design...in fact Chevy had several service bulletins and maybe even a recall in 69. Turns out 8-900 degree heat isn't good parts made of pot metal (though the base is alum). Regardless, there are a lot of 'service' carbs with 68-69 dates out there.
I've heard to stay away from Carter-built Q-Jets, but I've never read anything credible that defends this theory.
Lastly,..you want nothing to do with smogger Q-Jets (1975+). These are stamped "7045XXX" or higher numerically. The range of tune is lost, even on the idle mixture screws which are in the base plates.
Good base plates are easier to find than good choke horns, which are the softer metal, and have suffered years of over-tightening which causes them to "bow" in the front which leads to metering and vacuum probs.
You might pick up the book "Rochester Carburtors" by Doug Roe...great guide!
Good luck,
Wes
Thread Starter
Team Owner
Joined: Sep 2003
Posts: 88,393
Likes: 2
From: eville in
Originally Posted by 73, Dark Blue 454
The base plates are similar from 70-74. I believe all these have the brake booster nipple in the rear, unlike previous years. It's easily plugged with a threaded plug if you wish.
Stay away from 68-69 base plates. In these years, exhaust gas was routed through the intake to heat the carb for warm up and reduced emissions. A thin "heat shield" was sandwiched between two gaskets, but it was bad design...in fact Chevy had several service bulletins and maybe even a recall in 69. Turns out 8-900 degree heat isn't good parts made of pot metal (though the base is alum). Regardless, there are a lot of 'service' carbs with 68-69 dates out there.
I've heard to stay away from Carter-built Q-Jets, but I've never read anything credible that defends this theory.
Lastly,..you want nothing to do with smogger Q-Jets (1975+). These are stamped "7045XXX" or higher numerically. The range of tune is lost, even on the idle mixture screws which are in the base plates.
Good base plates are easier to find than good choke horns, which are the softer metal, and have suffered years of over-tightening which causes them to "bow" in the front which leads to metering and vacuum probs.
You might pick up the book "Rochester Carburtors" by Doug Roe...great guide!
Good luck,
Wes
Stay away from 68-69 base plates. In these years, exhaust gas was routed through the intake to heat the carb for warm up and reduced emissions. A thin "heat shield" was sandwiched between two gaskets, but it was bad design...in fact Chevy had several service bulletins and maybe even a recall in 69. Turns out 8-900 degree heat isn't good parts made of pot metal (though the base is alum). Regardless, there are a lot of 'service' carbs with 68-69 dates out there.
I've heard to stay away from Carter-built Q-Jets, but I've never read anything credible that defends this theory.
Lastly,..you want nothing to do with smogger Q-Jets (1975+). These are stamped "7045XXX" or higher numerically. The range of tune is lost, even on the idle mixture screws which are in the base plates.
Good base plates are easier to find than good choke horns, which are the softer metal, and have suffered years of over-tightening which causes them to "bow" in the front which leads to metering and vacuum probs.
You might pick up the book "Rochester Carburtors" by Doug Roe...great guide!
Good luck,
Wes
that why i need the spec's on the shaft's I may be able to save 1 or 2 for a good DD or better 
Melting Slicks
Joined: Mar 2005
Posts: 2,838
Likes: 10
From: Austin TX
The specs on the shafts never changed. It'd be nice to find a base plate that didn't need trottle shaft bushings...semi difficult job and you'll need to find some butterfly screws to reattach the butterflies.
Here's my favorite place for q-jet parts...great guys to work with and prices are pretty good:
www.weber-carburetors.com
They'll have what you're looking for.
Good luck,
Wes
Here's my favorite place for q-jet parts...great guys to work with and prices are pretty good:
www.weber-carburetors.com
They'll have what you're looking for.
Good luck,
Wes