Q-jet rebuild mini blog

mjsmith1223 · November 6, 2003

Hey all,

Just to keep the classics area cookin', I'm starting a Q-jet rebuild mini blog. I'll add stuff as I go. Maybe it'll help someone out someday.

The carb

The carb is marked as Carter Q-jet manufactured for GM. It's identical to a Rochester in all respects except for that stamp. The number is 17058204. That decodes to a '78 Chevrolet/GMC truck, 1/2-ton, 2WD with 350. While my truck is an '86, the motor is a mid-70's frankenmotor so this carb will work nicely. Got it off E-bay for $7.50

Getting started

Began by just reading everything I could find about rebuilding a Q-jet. Found that the info I had regarding rebuilding a marine Q-jet was the most helpful and detailed. Other than gaskets and venting, the street version is the same. Also found Mike's (Swervin' Ervin) stuff on his website regarding tuning to be helpful in learning why each piece is important.

Once the carb arrived I gave a real good looksy. For $7.50 I didn't expect much and half-expected to not be able to use the carb anyway. Turns out that other than being really dirty, it was in great shape. It was full of sand and gravel like it had been submerged in muddy water or something. All the linkages were present and accounted for, no binding, it had a hot air choke which I promptly converted to manual since my manifold doesn't have provisions for a hot air choke, accelerator pump moved freely, throttle valves opened and closed like they should, shaft bushings appear to be in good shape.

Disassembled the carb into the three major parts - airhorn, main body and throttle body. Secondary rod hanger appears to be an "O" and secondary rods appear to be CH. Can't tell what the primary rods are yet because they are too dirty to read any markings. Emptied lots of sand and gravel out of the body once I had the airhorn off. Used my forceps to pick larger pieces out of passages. I left the check ball in for now but will swap with the new one included in the kit. The screw that holds it in is small and I don't want to lose it, so I just left it for now.

Next up: Giving it a good bath/scrubbing and beginning the reassembly.

Mike

Grand Haven, MI

N2TRUX · November 6, 2003

Good reading Mike. You forgot a link to Swervin Ervins website though. If anyone needs info on 73-87 GM trucks, add this site to your favorites- http://www.73-87.com

mjsmith1223 · November 8, 2003

The saga continues...

Cleaning/scrubbing

Cleaned the carb last evening. It was about 33 degrees so I worked fast. Did you know that as carb cleaner evaporates it makes whatever its on really cold? I didn't think about that until my fingers went numb. The aluminum throttle body gets real cold, real fast - brrr! Anyway... It's clean, looks like a different carb. Got some canned air and blew out all the passages. BTW, also found that Break Free works just as good on carburetors as on my guns. It really loosens the baked on carbon deposits right quick and then a little elbow grease with a rag gets rid of them.

Assembly

Started the assembly process. Got the throttle body mated back up with the main body. Hung the float and measured. It was a little high, so I had to adjust it and repeat til it was right. Now for the part that stumped me. What's the secret to getting the power piston and primary metering rods in? I either couldn't get the rods lined up with the jets, or the power piston would pop back out of its seat and I'd have to start over. Ended up bending the primary metering rods - So now I get to buy new ones. Ordered them from Summit today. To avoid bending the new rods, is there a trick I'm missing? Or is it just the tedious process it seems to be?

Next up: Install the new primary metering rods when they arrive. Also ordered a B secondary rod hanger to replace my O hanger. My secondary rods are CH, which are dang close to DR, so I'll just leave them.

Misc

Got the truck ready for it's winter nap today. Filled the tank and put Stabil in it. Changed the oil. Changed the breather element. The air filter was new in August, so I left it until next spring. Checked out the leak in the rear diff cover and decided to leave it until next spring. Someone tried to seal it with black Permatex and I didn't feel like laying on the cold, damp driveway cleaning all that off before I could install my new gasket. Probably will put it in winter storage tomorrow afternoon.

Mike

Grand Haven, MI

mjsmith1223 · November 15, 2003

Continued...

Got the new metering rods from Summit yesterday. Dropped them in today. Got the airhorn back on. Silly me, I put the choke rod in backwards so I have to pull that and reverse it. Also got a new secondary rod hanger which arrived today. Current hanger is an "O", the new one is a "B". That will go on next and then I'll torque the airhorn screws, put the vacuum pulloff back on and then the carb will be ready to drop into my truck.

Mike

Grand Haven, MI

Larry · November 15, 2003

Good info…. hopefully it will help somebody.

I have messed with those Q-jets before. Took them apart…left them in the soaker for a day…tried to put them back together again and make them run right then gave up. Bolted on a new Edelbrock AFB and never looked back. From my experience, those 85 and 86 MY computer controlled feed back Q-jets are the worst of them all to mess with since you have 50 miles of vacuum hose to deal with after you get the carb to work halfway right.

For $200 a new Edelbrock is the only way to go if you must go the carb way. An EFI retrofit is the best carb rebuild you can give any old truck. I am converting my old 78’ jalopy with a late model big block with late model sequential fuel injection very soon. The engine is actually a 454HO crate engine but set up with 2000 MY L29 accessories. The engine is already in the truck but I am still collecting parts and working out the proper software right now. It will run a L29 intake and all the fuelie goodies but with a marine controller with remapped software for my application. I am in the middle of building a new house so the fuel injection retro is currently on the back burner until summer 04’. Until the house is done the wife says the big blue truck truck play money is a gonner.

mjsmith1223 · November 15, 2003

The fuel injection swap is interesting. I've thought about it alot. I wonder if a person could just get all the Ram Jet stuff from GM Performance Parts and go that way? Also given some thought to grabbing the engine and TBI setup from a newer truck (87-95). Or, maybe I'll just save a few more pennies and buy a '98 extended cab Z-71 and I'll be all set.

For now I'll have to stick with a carb setup. Currently I've got about $50 total into my "new" Q-jet. Since all the emissions stuff has already been removed from my engine, there's very little vacuum hose left to route. Mostly just ports to plug.

It's raining today and I have too much homework (down to my last three weeks of grad school), so I'll just have to make the carb project wait a week or so to finish it off.

Mike

Grand Haven, MI

jelisfc · November 18, 2003

The Qjet is easy once you take it apart and back together 20 times. I used the original off the 350 in my '78 when I replaced it with a built 454. Pre emissions so it was simple. I rejetted the front and put in larger secondaries. I got the kit from a place in California. I just about through the extra pieces this weekend but since the motor and carb are still under my workbench I decided to hang onto it. I tried the Qjet from the 454 first but the one from the 350 rejetted ran better.

If done right a Qjet will perform great. I've run numerous Hollys and even a Predator and for overall streetability I kept going back to the Qjet. I estimate the engine was good for 450 Hp and besides a high volume fuel pump I never had a problem running to 6000 rpm.

If your aftermarket version has the top air plates on the secondaries adjusting the spring tension will effect how quick they open. Before I figured that out I had a lag and when they opened it really hammered the drive train...bad enough to snap the pinion during a full launch in granny low!!! Oops.