Tips wanted for rebuilding a Q-Jet

[C10Silverado79]

So far I've replace the water pump, fuel pump, belts, hoses, shocks, and brake system (except MC - hard lines - vacuum assist). I think it's time to rebuild the Q-Jet. Any advise or Tips-n-tricks for rebuilding the carb will be appreciated. I rebuild a 2bbl on a 250ci about 18 years ago so to say I'm rusty would be a gross understatement. I'd prefer not to spend the $$$ for a rebuild carb if I can help it so I'll try the self-rebuild first.

Are there any particular brand of rebuild kits that are better or more complete than others?

Any "gotchas" I should be looking out for?

All advise is welcome.

TIA

[datguysaL]

i did one this past saturday, a rochester quad. only thing i could think of as being the most delicate is the plunger. and well buy yourself a gallon of the dip clean stuff.

[ray_mcavoy]

Hi C10Silverado79,

A few things that come to mind:

(1) I've used Napa, Carquest, and Standard/Hygrade kits and can't really say that I've noticed much difference in terms of parts content or quality. None of them include a float though. You have to buy that separately and I highly recommend putting in a new one with the rebuild.

(2) GM used Q-Jets on a wide variety of applications. It'd be a good idea to look up your carb number to see if it's original (or at least somewhat close) to your application.

(3) Also look up the stock rod/jet combo for your carb number (I've seen a table of this info listed on various websites). Usually, staying close to the original rod/jet combo will obtain the best performance.

(4) After cleaning the carb in chemical cleaner, use compressed air to blow out all the passageways and openings.

(5) When installing the air horn gasket, make sure it doesn't interfere with the movement of the power piston / primary metering rod assembly.

(6) If the throttle shaft holes are worn in the baseplate, you don't have to buy an expensive bushing kit or send the baseplate off to have bushings installed. Here's a tip I picked up from Dave Ray (Ignitionman) on another forum ... the base plate bores (from the factory) have a stepped area that's .030" larger than the shaft. You can make "bushings" from a sheet of .015" teflon that fit right into that stepped area (no need to bore out the holes). I've done this on a number of Q-Jets with loose throttle shafts and it works great!

[Restrorob]

One thing I can add;

After so long the small welch plugs on the bottom of the carb body (float bowl area) start to seep fuel, This can cause pro-longed cranking if left set for a few days because the fuel leaks out of the float bowl into the intake, These can also cause a slight drop in fuel mileage as well.

While you have the carb tore down and after soaking/cleaning use a two part epoxy or we use JB-weld and cover these welch plugs, It's really not necessary to cover the two large ones in the center but a thin coat wouldn't hurt....

[ron350]

Buy the Doug Roe book and save your self lots of grief.
Having the instructions and pictures is almost a must for first time rebuilder.

Wonder if Doug is still around?

[Restrorob]

Here's a rebuild article I found right quick;

http://www.corvettefever.com/techart...ild/index.html

[C10Silverado79]

I appreciate all the info. keep it coming. Now who is Doug Row and what book are you referring to?

Thanks
Steve

[ron350]

Just google Q-jet book or Doug Roe.
Shoot you may be able to find a free down load showing how to rebuild one.

My 1973 copy.



Guess this is the latest copy.

Amazon.com: Rochester Carburetors...

[C10Silverado79]

Originally Posted by ron350

Just google Q-jet book or Doug Roe.
Shoot you may be able to find a free down load showing how to rebuild one.

Guess this is the latest copy.

Amazon.com: Rochester Carburetors (0075478630141): Doug Roe: Books

I want to work on this over the weekend and don't know that I'd get the book by then from online. I did some quick checking and amazingly enough, I found a copy at the local Borders. It cost me a couple $$$ more than online ($20) but I already have it in my "grubby little hands".

You can make "bushings" from a sheet of .015" teflon that fit right into that stepped area (no need to bore out the holes). I've done this on a number of Q-Jets with loose throttle shafts and it works great!

Ray, That sounds real simple but when I think about it, I'm not so sure. First off, where would I find a sheet of .015" teflon? Second, how did you trim the teflon to may a correctly sized, round, bushing? (I'm assuming they are round.) Just having a little trouble wrapping my head around that task.

Thanks
Steve

[1985-GMC]

Originally Posted by Restrorob

One thing I can add;

After so long the small welch plugs on the bottom of the carb body (float bowl area) start to seep fuel, This can cause pro-longed cranking if left set for a few days because the fuel leaks out of the float bowl into the intake, These can also cause a slight drop in fuel mileage as well.

While you have the carb tore down and after soaking/cleaning use a two part epoxy or we use JB-weld and cover these welch plugs, It's really not necessary to cover the two large ones in the center but a thin coat wouldn't hurt....

I wouldn't use jb weld because gas will soften it and soak through it so use a gas friendly 2 part epoxy. And muscle car did an episode on rebuilding q jets, it should help you out some. http://www.spike.com/full-episode/qu...-rebuild/33035

[ray_mcavoy]

Originally Posted by C10Silverado79

Ray, That sounds real simple but when I think about it, I'm not so sure. First off, where would I find a sheet of .015" teflon? Second, how did you trim the teflon to may a correctly sized, round, bushing? (I'm assuming they are round.) Just having a little trouble wrapping my head around that task.

Thanks
Steve

Hi Steve,

The original post I read mentioned getting teflon sheet stock from a hobby store. But I live out in the sticks ... no hobby stores around here. So I found some from an online mail order place called Small Parts Inc. (www.smallparts.com). Part number STE-0015-A for a .015" thick, 6" square sheet. They also carry 3-48 x 1/4" button head screws (part#BCAS-0348-04-25) that work great for re-attaching the throttle plates to the shaft. The ends of the original screws are peened over so they won't back out ... carefully filing off the exposed threads will make them much easier to remove without snapping them off.

The counterbored stepped area in the Q-Jet baseplates is around 5/16" to 3/8" wide if I remember correctly. So to make the "bushings", just cut a strip that width from the teflon sheet (cuts easily with scissors). Wrap the strip around the throttle shaft and cut to length so it doesn't overlap or leave an excessively large gap between the ends.

I thought it sounded like more of a complicated process when I first read about it too.

Ray

[ron350]

1985-GMC like you said I could never find a glue that would stay on those secondary well plugs.
There has to be a gas proof glue that will stay on those plugs.

Do you have the brand name of the gas friendly epoxy?
My computer will not open your link.
Thanks
Ron.

[1985-GMC]

I found some two part epoxy at napa a while back that said it was gas proof but I have no idea what the brand was sorry, and I dont know about the link it works for me try Googling "muscle car Q-jet rebuild".

[C10Silverado79]

Hey guys,
thanks for all the tips and suggestions. I got the rebuild done and the carb back on the truck. I pulled the carb off late yesterday afternoon and spent last night and today working on the rebuild. ( I'm real slow when I don't know what I'm doing) Disassembly wasn't too bad and I was trying to remember to take some pics in case I needed them for assembly again. (I did refer to them several times - digital camera are great!) The carb was pretty bad with a lot of crap inside. I'm surprised it ran as well as it did. I took me a while to get the everything cleaned up enough. I ended up taking an old tooth brush to it. Soaking and spraying just didn't do the job.

Assembly wasn't perfect but went ok and I only had to partially disassemble it once. http://67-72chevytrucks.com/vboard/i...ilies/wink.gif I epoxy'd the plugs and let them dry overnight. Got hung up a little reinstalling the choke coil. Got the air horn on and choke connected, looked around and realized I didn't put in a round plastic piece that goes next to the float bowl. Now that I had an idea what I was doing, taking it back apart and rebuilding again wasn't that bad.

Put it back in the truck late this afternoon. I also put all new vacuum lines on. I noticed the vacuum connection for the cruise and (trans?) was loose so I put sealer on the threads and tightened it up. I also capped the line for the CC until I decide if I'm going to try and fix it or replace it. I put a new vacuum line brake booster and replaced the booster filter as well. I couldn't find any teflon and didn't have the brass inserts available either. I couldn't really feel or see any noticeable play in the throttle shafts so I left them alone. If necessary, I'll go back in and do them later.


Finally, the moment of truth arrived. Once the fuel got the the carb, it fired right up and idled very smoothly. My initial shake down run was real good. The truck ran very smooth with decent acceleration. It actually feels like a 350 now. It's no rocket sled and I don't think I could burn up the tires but that not my goal. I'm not sure if there is any tweaking I should do but it can wait a bit. I'm going to run the truck this week to see how it behaves and monitor the MPG. All in all, I'm please with how it went and the results.

Thanks again for the help.

Steve

[1985-GMC]

Glad to hear you got it rebuilt successfully, good job.