Hey guys. I've got a 4bbl quadrajet on my 78 w200 (318). I was wondering if anyone had any tips on tuning them because frankly I dont have a friggin clue as to where to start. I know there are two small screws on the baseplate in the front of the carb and one in the center that drops down to the float. Then there is the idle adjust screw on the side and another screw on the opposite side. I'm not sure how to get the truck running properly. I just rebuild the carb and it runs nicely but the exhaust smells awfully rich to me. I've also got to get to the timing because its way off to. Do you suggest I set the timing correctly before messing with the carb? If so, I'll do it, but i'd still like to know how to tune it. Thanks felluhs.

Or this being a GM carb, would I have a better shot going over to one of their boards about this?

Summit or Amazon.com sells Q-jet books. I think you can help Moparts by ordering from this website. Someone who is a Pontiac racer used to have a website that was great with Q-tech.
BUMP^

1UglyFish - thanks for the info. I have an 1985 Dodge Truck (318 V8) that is equipped with the Q-Jet, & the tuning info you provided is very helpful.

Glad to help.

It's a rare occasion that a former Chevy Rat has any real input, but this Qjet stuff is my old backyard.

I thought of one other quirk these Q's have in common. If you remove the carb and inspect the underside, you'll most likely find a good build-up of carbon right in the center cavity. Clean this out completely! It has a vacuum orifice that assists in allowing fuel into the secondary bowl. I've also found that a heat shield and a wooden spacer do wonderful things for economy, once everything else is dialed in.

Don't let anyone tell you to get rid of it! It is excellent at low RPM mileage and there's nothing that flows more at WOT (factory). So, enjoy!

Good advice from Iuglyfish and yes, DO set the timing first before tuning the carb.

1UglyFish -

Several years ago, I installed a used Edelbrock Performer intake and an rebuilt Q-Jet carb on the 318. The Q-Jet was off of a late 80s Dodge Truck with a 360. The guy who rebuilt it (Chevy guy) installed the jets from a 327 carb. My mileage and power both went up - I am totally happy with the Q-Jet and I highly recommend this carb to everyone.

Right now, I have several tuning issues.
- when I start the truck on a cold winter morning, the truck will idle extremely rough, so I have to step on the gas to increase the idle speed (when I start the truck during a warm summer morning, the carb will kick into a normal fast idle)

-sometimes when I drive away after a cold start (mostly when it was wet out), the engine stalls and is hard to restart. -- after a cold start, I start driving, the truck will hesitate badly until the engine reaches operating temp.

- once in a while, the truck starts a little hard when it is warm. When I first got the carb, it used to start perfect everytime - cold or hot.

Personally, I think the carb is a little lean. I also have Hedman headers, so the lack of a heat riser valve isn't working.

Thanks again 1UglyFish - I enjoy reading your posts on Moparts.

"then the secondaries must open fully"
The secondaries should open to 90 degrees, but the air valve may not - this is mixture bias device, not a malfunction; depends on the motor. My 455 Buick is supposed to and didn't - I filed the stop to allow it to move to vertical.
"And if it is too loose, you'll flood the cylinders"
If it's too loose, you'll have a lean stumble caused by too much air and not enough gas. Too tight and the response will be OK but you'll lose some flow - but with a 318 you have more than you need anyway.
The usual pre-load of air-valve tension spring wind-up against lightly closed is about 1 full turn (360). If it bogs when fully warm, tighten it a very small amount and try again.