Help me set up my new (to me) Quadrajet

[El_Diablo]

Hey guys,

Just picked this thing up, never messed with them much. I'm mainly just wanting decent mileage and a stable off road carb.

What i have is a 85 amc 360 with an edelbrock performer intake (non emission), stock cam, stock heads, exhaust plan is a set of hedman headers into 2.5 inch pipes that will merge into a single 3 inch exhaust. Only other real mods are a TFI system and possibly an MSD off road box in the future. I am not running ANY emissions equipment.

So are there any Q-jet experts up to the task?

What im looking for are mainly jet and rod recommendations aswell as float level recommendations and any off road tips tricks or mods that would help. Mileage aids are also welcome as long as they dont distract from power and off road ability.

Any and all help is appreciated :thumbsup:



Thanks,
John

[pineymike]

Get one that would go on a 305 chevy and use a pressure regulater run it at as low a setting as you can off road[trial&error] then boost the pressure on road,I've had good luck with this setup on a few different motors.Have fun!

[Dr.E]

Which Q-jet do you have? What engine and vehicle was it originally installed.

[Murphy]

Get one that would go on a 305 chevy and use a pressure regulater run it at as low a setting as you can off road[trial&error] then boost the pressure on road,I've had good luck with this setup on a few different motors.Have fun!
That's interesting. Why do you say a 305 and not a 350 that would be closer in displacement? Too rich?

[El_Diablo]

originally it was from a 1980 350 mated to an auto trans

[Dr.E]

1980 what vehicle? The reason I ask, is because you not only want to match displacement, but similar weight and gearing of donor vehicle. If you use a quadrajet from a 1980 corvette with 350 and auto trans with 4.10 gearing,
that carb (jet/metering rod) combo would dump too much fuel too soon and not perform well in your application. Look for a OEM application that most closely matches what you are running if you want a close match(starting point).

[El_Diablo]

i already have one, hence the need for jetting info ;) i will not be buying another q-jet

there is no way to tell what vehicle that it is off of unless you know something that i do not? im just looking for a good idea of jetting and rods on a lightly modded 360.... someone has to know a good base setup on a q-jet

[Murphy]

I was hoping someone would post some q-jet tricks too. All I can suggest is run it like it is watching for leaks, poor idle/vacuum/performance, and after about 50 miles or so check the color of your plugs. Then try to fine tune it from there if you need to, first taking careful notes of all the stock jet and metering rod sizes so if you go the wrong direction you can go back to the stock settings and start over from there.

http://www.digitalcorvettes.com/forums/showthread.php?t=88376

[El_Diablo]

carb is junk and cracked, im pissed that i wasted $40 on this thing, theres also a screw that i cant remove at all :mad:

im trying to get another similar carb and i'll combine the two i guess :mad:

[Dr.E]

There are a lot of tuning methods for Q-jet carbs. You can't over simplify the process if you wan't to get all that these carbs can offer. Thats why some hate them and some have tuned them to power cars into the low 10's in the quarter mile. You cant just pick a combo that ran well on my truck and expect it to perform as well on yours. You already have your starting point!
Rebuild what you have then tune idle. Start off with soft power piston springs p/n 7037851 (leaner)when using larger cams then move up to 7029922 med/soft if needed and stiffer if your cam is closer to stock. Remember larger cams make less vacuum at idle hence the softer spring. Stay as lean as you can here. I'm making some huge assumptions here, like you know how to tell if your idle is rich or lean, but if you want the "cliff notes" tuning version I'll have to make these assumptions.
Next the main(primary) metering rods. These are the things attached to the power piston, the thing you just changed the spring on. If I knew what you had I'd suggest getting some richer and some leaner so you can select which runs better in your application. For the sake of argument let's say you have a 44B rod then I would suggest getting a 46B (leanest) to a 42B (richer) and 40B (richest). Try what you have, if it seems "flat" on acceleration try leaner then richer. Next primary jets (the screw in brass things that the primary rods fit into).
Most 350's use a #69 or #70 these are on the leanest end of the spectrum.
Try leaner (ie #69) if you are at a#70 to see if performance improves,then try larger. See a trend here...leaner then richer...leaner then richer.
It is the combination of the rod and the jet that makes the tune. I could imagine several combinations that would run equally well that's what makes tuning fun or torture. The seats that come in most rebuild kits are restrictive and only used on a stock rebuild. The better one to use is pn7035140. Set float level to 9/32's if it's set too high fuel will slosh into the power valve hole and overly enrich your mixture.
Generally the secondary metering rods that work better for off road are the shorter ones. Stay away from the longer power tips they allow more fuel earlier. These are stamped with letters like AY (most stock 350's) Again try a thicker rod (leaner) then a thinner rod AT (richer) and tune for best WOT performance. Use wide band O2 sensor, read spark plugs, time runs with a buddy and a stop watch to determine best tune. There are many other little tweaks for max performance, but start with what you have. Make notes of what is stamped on these parts in your existing carb and take it from there. There are very detailed books on tuning available at your local book store that can walk you thru the fine details.
Just to give you the motivation to get "into" this: When I finally got my Q-jet tuned to perfection I could not believe the performance difference.
I could say that just the "seat of the pants" feel was as if I was running a V-8 vs a stock 6 cylinder motor.
JUST READ YOUR LAST POST. STOP DON'T THROW OUT THAT CARB!
You can use the jets,primary and secondary metering rods to help you in the tuning process.
At least you will have more parts to choose from.
Now look in the junk yard for a Q-jet off of a mid 70's 4x4 with a 350 or a HEAVY passenger car this will get you closer to what our FSJ's like.
Sorry about the crack!

[El_Diablo]

dont worry, i wont be throwing it out at all, i will be rebuilding it using parts from a new carb, its actually very similar and from a 77 truck, looks like they used the same settings from the truck to the vette so i should be fine rebuilding to stock spec's and tuning from there

i tuned my 2150 well enough to get 14.85mpg out of a tired 130k mile motor and horrible transfer case through a restrictive exhaust and the only mods being an edelbrock intake and a tfi setup with resistor plugs.... not bad from the 8.3mpg i started with.... i know how to tune but i haven't messed with q-jets before and that is where my trouble lies

im not looking for something that is a universal tune, im looking for a ball park to start out with but i guess i'll just go stock for the carb and move from there

thanks for your help, wish me good luck on winning the bid on this other carb!!

[pineymike]

I sugested a Qjet from a 305 as a simplified way to get a carb tuned for decent mileage as stated in El Diablo's original post.I don't belive performance would be affected at low rpm offroad maby at hwy speed&towing I've had good luck with this set up on chev 350's in late '70's chevy pickups that are probly not as aerodyamic as the bricks we drive and no loss in"seat of the pants" performance.Qjets are great carbs often over looked.Good luck have fun!

[Murphy]

I love the performance of q-jets but unfortunately not very good at tuning them. For now.

[joe]

Doug Roe wrote a good book on Rochester carbs published by HP Books. Think it's just called "Rochester Carburetors" Lotsa good info there. Worth buying if you run a QJ.
So far as using a QJ from a 305..I dunno. Mine came off a mid 70's 425 Caddy and after rebuilding it works great on my 360.

[Murphy]

I think they are all pretty much the same except for some small differences between earlier and later models. It just depends on what it came off of as to what jets/metering rods it has, and as soon as you tune it for your engine all that is out the window. Truck metering rods are a little thicker and designated with "M" series sizes I think. More lower end.

These carbs are more complicated, but better performance always is. Haynes also has a Rochester manual. It usually has to be ordered. How To Rebuild And Modify Rochester Quadrajet Carburetors by Cliff Ruggles is also supposed to be a good book.

[El_Diablo]

im actually wanting to pick up the how to tune and modify book.... still on the hunt for another q jet

[Murphy]

im actually wanting to pick up the how to tune and modify book.... still on the hunt for another q jet
I just ordered it from Amazon.com, grab one.

http://www.amazon.com/Rebuild-Modify-Rochester-Quadrajet-Carburetors/dp/1932494189/ref=sr_1_1

[Murphy]

El Diablo, I just rec'd the Haynes Q-jet and the Rebuild & Mod books. I'm impressed. I would have gotten the Rochester book that Joe suggested also but I had already ordered the two books I just got. I'll get it next time I order something from Amazon.

The Haynes seems to be geared more for beginners as most Haynes manuals are, and that is perfect for me. It covers all the carbs including the 1 & 2-barrels and even has a trouble-shooting and basic modifying section also including cam selection pages. The Haynes was a real surprise.

The How to rebuild and modify a quadrajet book is more in-depth with full color pictures and has a more extensive modifying section including full race mods. It even covers Edelbrock quadrajets.

I highly recommend both books. :thumbsup:

[El_Diablo]

good to know, im waiting on my other carb to come in the mail, headers are here though :thumbsup: