Darrel1

Does anyone have a link to instructions for rebuilding a Q-Jet carb for a 1980. I have searched the archives and found a bunch of discussion threads, but could not find any instructions.

The carb runs fine, but is very dirty and has probably not been touch in many years. I just bought the car this fall. I have taken the intake and valve covers off to clean and repaint- thought I would do this while the carb is on the bench. I have the LARS instructions for tuning the choke.

Thanks for any links??

Garys 68

Sorry, no links.
Get the S/N off the carb, go to the auto parts store, buy the kit.
It comes with pretty good instructions.

Darrel1

I have never taken apart a carb before. Are the instructions easy to follow, or do they assume you know certain steps they do not mention?

Boofers

Garys 68 is right.

Here is some additional info, look under intake and tuning - Corvettefaq Engine Topics

This article is very good, I recommend you read it before you start the rebuild - Lars QJet Tuning Paper

lars

It assumes you know certain techniques and basic assembly process, and it assumes that you have a carb that is not exceptionally messed up...

The biggest thing I see on these carbs is that they are old enough that a lot of people have done a lot of "creative" things to them. That means that you cannot assume that what you see when you take it apart is correct: the carbs will have wrong jets, rods, and other parts in them, and a lot of the parts are pretty screwed up. Often, unless you know what the parts are supposed to look like, you will not know that something needs to be fixed or replaced, and you'll end up re-assembling the carb with the same errors in it. It is vital that you know the correct jetting for the carb you're working on and that you take a critical look at all components. Be sure to replace the float with a correct NitroFill float (part number 2-442), and set the float level to .420", regardless of what spec you see elsewhere.

Kalway

Quick question, is it a 305 or 350? If it's a 305, you've got an E4ME (computerized q-jet) on there. If it's a 350 you're blessed with the friendlier non-computerized q-jet. If it's not an E4ME then fix it up and make it run nice.

Darrel1

It is the 350. Thanks for the help. I am going to order the parts today.

Darrel

Gator81

Agree with what the others posted, but wanted to offer an additional suggestion: get the book "Rochester Carburetors" by Doug Roe. Besides all the basics, you will get lots of practical advice and photos. The step-by-step advice in that book is unbeatable, IMO.

Take it slow, work in a well-lit, clean area, and follow Roe's step-by-step advice, you can't fail.

good luck!

comp

let us know how it goes

Darrel1

Thanks for the advice. I am going to order the book.

stingr69

I have that book but pay attention when you take it apart. There are some specific 1980 details that are left out of that book. Count the number of turns when you unscrew things inside the carb. There is a "thingy" in there that was set by the factory and the book and instructions will not tell you how to adjust it. I just guessed the number of turns. Might be why mine does not run as well when cold now.

-Mark.

Easy Mike

There's a good reference book on Q-Jets. If memory serves the title is The Rochester Quadajet or something to that effect. Lots of good reference pictures.

Tom454

It's called the "APT" (adjustment part throttle), and if you turn it to remove it, you're going to have trouble. -I think- this was on the electronic carbs though, not the old non-electronic versions.

The adjustment is made at the factory using specialized equipment and can only be "guessed" at if you mess it up. It can cause the engine to flunk emissions as well. Ask me how I know. I have this on my 86 305 Silverado.

If yours has no wires going to it, and no visible electrical connections on the outside, then don't worry about it... maybe.

lars

Tom -
All Chevy passenger car Q-Jets from 1975-up have the APT - not just the ECM-controlled carbs. There are 2 versions of the APT: One is a brass adjuster located just forward of the power piston. This one sets a lower stop limit for the power piston, thus setting part throttle (cruise) mixture. It has no effect on WOT mixture.

The other configuration has no piston lower stop limit, allowing the primary rods to pull fully into the jets. Instead, there is a second metering jet in the forward passenger side corner of the float bowl with a large, round insert above it. This insert is a spring loaded "metering rod" that is adjustable from the top. The position of the rod in the "jet" changes mixture across the entire operating range.

For emissions purposes, the only way to adjust either of these settings is with a 4-gas analyzer. If emissions are not a concern, you can knock the cover plugs out of the carb airhorn and gain access to these adjustments from outside the carb. You can then set them up for best throttle response and drivability, which will not be best emissions...

Tom454

Yeh.... what he said.

DaveL82

A couple of things I do to help when disassembling:

1) remove the screw that attches the rod to the choke flap. This leaves the rod with the main body when you remove the top section.
2) us a puch to drive the accelerator arm pivot pin towars the air horn. However only push it in enough to push the pin past the lever. You'll use a screw driver against the air horn to push it back later. This frees the arm from the base.
3) there will be two screws in the ari horn that are hard to see.
4) I find it easiest to remove the secondary needle hanger and rods before disassembly and replace last.
5) Do not adjust any of the screws inside without proper equipment, only ajust float height and external idle mixture adjust.
6) Rare that the idel caps are still covering the idel screws but if so nows the time to get them out.
7) Never force anything! The air tubes are fragile.
8) coat the main well plugs with JB Weld while a part.
9) with the top cover removed you see the main needles and piston which come through the gasket. If the fiber plug is old it may not hold the piston in when the gasket is removed. Don't worry the new gasket will help hold it in place when reassembling. The key is making sure it stays in enough to keep the needles in the jet or else they could get bent.

Note that I use a small puch on the aluminum at the very top to help hold it in but don't recommend for a beginner since you may do more harm then good.

Most of all take your time and if you get stuck get back on the forum and ask.

Dave

Darrel1

Thanks for all the advice.
I have decided to read the book Rochester Carb book first and relate it to the suggestions on this post, before I start. I decided this because a lot of the terminology used on this post I am still trying to figure out. I need to figure it out in the book instead of a torn apart carb on my bench!!

I have more time than money right now!!

TedH

Lars rebuilt/re-jetted the q-jet on my '80 L48. Swapped main jets, main and secondary metering rods for those that I had; no extra charge for those items as long as I sent back what I removed.

I am sending my '69 q-jet and points-style distributor out to Lars this afternoon.

Lars has made me a believer in a well setup q-jet; even though my brothers all prefer Holleys.