Originally Posted by wyoben

Howdy all Im brand new here , mainly here to learn from the Guru Lars about Qjets , I will try to cut to the kill here , and I apologize , I wanted to start a new thread like Lars suggested , but I failed to figure out how on this forum yet .
I am trying to refurbish carb # 7045213 to use on a convertable 70 GTO w/ a 1974 400 w/ 4x heads edelbrock performer int. HEI dist, this is a temporary engine setup for now. I have a few questions , and I will try to attach a few pix to explain , the thing that threw me is the needle and seat ? Ive never seen anything like it , notice the pix , the rubber seat end is not tapered ? , however it looks like it might seat, the top is rounded ? and had NO clip , it looks like it might function , but Im wondering if I should put a Normal needle/seat in it .
heres some of the specs on the carb for now , it looks like 71 primary jets , w/ 393 ? primary meter rods { man those numbers are tiny ! } for the life of me could not find markings on sec. rods , but hanger # 33797 suspends them, I know Lars advises against the truck carbs , however I miced the primarys and they miced out at.026 ? , so those are the decent primary rods , correct ? I cant remember from the article , for right now I just wanna get this thing running , it will mainly be run at high altitude between 4500 - 7500 plus feet, again this car has been a jigsaw puzzle for 30 years , and all the pieces i thought would be a breeze to work with have kinda bit me ...oh well, I do have a kind of rare ? 7040507 70 vette manual carb , that I may rebuild or try to trade a vette guy for a 70 goat carb . I have toyed w/ these qjets before , but left off 30 plus years ago, however I did find a nice stash of oem qjet carb parts stuff
anyway I believe that covers that , anybody ever seen aneedle /seat like this ? thanks to All !

Originally Posted by twinpack

Not meaning to hijack here, but Lars I wanted to thank you for going through my carb. I completed the L79 rebuild and had it dyno'd. The results were very satisfying to me. 386 hp, 428 ft. tq. The machine shop owner said the Q-jet carb ran beautiful with a crisp response. He ran the motor to 6500 rpm and the only resriction was the stock 327 manifold. So thank you. I truly appreciate your expertise.
Peter

Originally Posted by lars

From time to time, I try to post up some of the recent observations and issues I see when rebuilding Q-Jets. As noted in my earlier posts, more and more of these carbs have been subjected to some really bad previous rebuild attempts, so it is no longer possible to simply disassemble a carb, clean it up, slap a “kit” in it, and put it back together to make it run right. Every carb must be carefully examined to find all the issues and errors induced by the past 20 guys who have messed with it, and all these issues must be correctly repaired. Often, parts must be replaced, since people will actually destroy parts in the carb when working on them.

I posted a few interesting notes and findings about Phil’s (“Philgran’s”) carb in his post here – this is worth checking out if you haven’t already been following the thread:
https://www.corvetteforum.com/forums...979-l48-2.html

This next carb comes from Derrin, whose wife just picked up a ’76 Vette with a badly-running QuickFuel carb. Derrin found a nice, used, original 1977 Vette California carb, which looked like a solid, rebuildable carb that would be perfect for his application. The carb was really dirty (which is good – it usually means it hasn’t been messed with), but all parts were there.

Upon disassembly, it became obvious why the carb was removed from service and put up for sale: The previous builder had caused so many problems with the carb that there is no way the carb could have run. If it was running, it was running so badly that the car would have been nearly inoperable. I’m sure someone was saying, “It’s that $%#^!! QuadraJunk Carb – those things are all crap!!!”

Here’s what I found:

• They installed the incorrect fuel filter: 1966 – 1974 Q-Jets take a “short” filter. Starting in 1975, they went to a “long” filter. The builder of this carb put a "short" filter into the long inlet housing, which allowed all fuel to bypass the filter, filling the bowl with dirt and debris.
• They failed to install the seal on the carb inlet fitting – the carb would have had an incurable fuel "drip" at the inlet in spite of the fitting being tightened so tight I could barely get it out (they really tried to stop the leak..!). I used my ½” drive impact gun to remove the fitting.
• Choke intermediate shaft seals were not installed, allowing dirt ingestion into carb.
• The idle mixture screws were grossly misbalanced - all idle fuel was being metered on one side of carb only – idle fuel was shut off on the other side.
• The Choke Pulloff was intentionally disconnected and disabled – the carb would have had horrible flooding at cold start, with no control of the secondary airvalve.
• The Power Piston Spring had been intentionally stretched out and destroyed. Here is the damaged spring on left. A stock, correct, unaltered spring is on the right. The stretched spring would cause the power piston to never seat, putting the carb into a permanent rich condition:
  
  
• The Power Piston hanger arms were intentionally bent upwards, pulling the rods permanently out of the jets – the main metering system in the carb was basically inoperable, and the carb was running in a massive full-rich condition with no rods in the jets. The "rebuilder" probably was unable to get the rods to slip into the jets at assembly, so the problem was solved by bending the hanger arms. This actually made the stretched-out spring somewhat irrelevant, so it solved that problem, too...
  
  
• The Accel Pump diaphragm was collapsed – accel pump inoperable.
• The Float had been bent to lower it so far that it was bottomed out in the bottom of the float bowl – I’ve never seen a float level so low. Probably lowered in an attempt to compensate for the rods not being engaged in the jets.
• Undersized jets installed. They dropped some really small jets into this thing to try to fix the other problems.
• Very low APT (power piston height) setting, further running the carb lean (if the rods had been in the jets...)
• They also bent the Secondary Hanger arms with 1/8" difference in height from left to right – the one side of the carb would have run prematurely really rich, with the other side of the carb running super-lean at wide open throttle.
• Not caused by the previous builders, but the carb had severe corrosion on all parts - all steel parts covered in rust, and all aluminum/zinc parts covered in oxides.

I’m going to have to replace the power piston spring, but all other items can be fixed and corrected. The carb just came out of the de-rusting tank, and is actually looking pretty good. Later today, the carb should be up and running on the test engine, and I think Derrin’s wife is going to have a really nice running carb.

So look closely and critically at those carbs and carb parts when you tear into your Q-Jet during rebuild: The object of the game, and the only way to make these carbs run right, is to find all the horrors induced by 40 years of bad work, and bring these things back to life. And make sure you know the correct, original specs for the carb you're working on (that applies to you Holley guys, too...) - most carbs have been altered, and you cannot assume that the jets and rods in any carb are correct for your application.

As always, feel free to contact me if you need assistance or comments as you work on your own carbs.

Lars

Originally Posted by tjmaniez

Lars your PM's are full but are you still accepting requests to rebuild Qjets? Would love to pay you to have a look at mine.

Originally Posted by riverracer au

Lars doesn't do PM's.

best to email him on V8FastCars@msn.com and ask him for his services papers

i'm more than happy with his rebuild on mine, received carb back and bolted on, fired straight up, hasn't missed a beat.
also had my points dissy rebuilt at the same time.

Originally Posted by stumpshot

Uh-----what is a "points dissy" ???

Originally Posted by jim2527

Pre-HEI distributor with points = 'points dizzy' '68-'74 points. '75-'82 HEI