Quadrajet or Quadra-throw out the dang window!!
 

I have seen many issues with the Quadrajet carbs on this forum, and using other peoples experience, I've been able to narrow down the problems, but I'm STILL having some issues tuning in my carb. I know it can be a great carb, but I'm still learning how to get it tuned in.

Here's the issue. Cold starts. In the morning, my truck takes 3-5 crank sessions of 10-15 seconds each to get Murphy(or so my wife has named it, relating to Murphy's Law:lol:) just about running with about 2-5 minutes of staying on the throttle to keep it running.

Once it's going, it runs. I stopped/started the engine 8 times in one morning and cranked up every single time. Although, it idles higher than "feels" right and kills the motor when cold, which leads me to a vacuum leak. Here's the skinny on my labors thus far.

1972 GMC 1500, Goodwrench 350(Stock), Quadrajet Carb w/ electric choke(Turned two notches to the rich side, verified operational), TH-350 Trans. Timing set to 12 degrees w/ vacuum tube removed during timing setting, running 87 pump gas, very mild aftermarket intake manifold, dual exhaust with some knock off aftermarket mufflers, fairly free flowing.

1. New Fuel Filter w/ the spring loaded stop valve built in.(No visible fuel leaks from tank to carb)
2. Rebuilt Carb, new gaskets, power piston, epoxied the plugs inside.
3. All vacuum ports either used or capped
4. Brand new fuel pump(1 week old)
5. New primary needle spring(It was missing it completely upon rebuild)
6. Checked for vacuum leaks with none noticeable
7. Both idle screws turned out 4ish full rotations
8. Secondary needles set to bottom out at zero throttle
9. Epoxied the 'plug/cap?" just outside the fuel line housing. The plug/cap sits dead center on the carb on the front(I thought there might be a leak there and the previous owner epoxied the same area.)

So, lump sum, hard starting in the morning(Dry carb bowl?) and idles low, idles high when at operating temp, but, runs well on the road and in gear/with a load.

Let's hear it ladies and gents, lay it on me!!!

Re: Quadrajet or Quadra-throw out the dang window!!
 

Are you sure about your timing?
Have you verified your timing tab is accurate?

Re: Quadrajet or Quadra-throw out the dang window!!
 

I was in the same boat as you.. rebuilt the carb 2 times, and adjusted it for months before I finally dialed it in.

Do you have the Cliff Ruggles book? Or gone to his sight.. loooots of good info there.

http://www.cliffshighperformance.com/

I also had to adjust my APT setting..something I learned in the book and from the site.

Don't give up..

Re: Quadrajet or Quadra-throw out the dang window!!
 

The solution to your problem is spelled
H O L L E Y

Re: Quadrajet or Quadra-throw out the dang window!!
 

This :D anything of mine that's carb'd has a Holley. Finicky, but damn reliable.

Re: Quadrajet or Quadra-throw out the dang window!!
 

Yup... Tuning a Holley isn't as complicated as tuning a Q-jet, but everybody thinks Holley's have to be tinkered with constantly. Not true. :)

To the OP... one thing that Q-jets will almost always need is the throttle shafts rebushed. They are a 30 to 40 year old carb depending on what rig you have or got the from. So a lot of wear in those throttle shaft bores. I also agree with getting Cliff's book as listed above. Keep at it... those Q-pukes are great carbs once dialed in. :)

Gary

Re: Quadrajet or Quadra-throw out the dang window!!
 

http://www.amazon.com/Rebuild-Modify-Rochester-Qua...Dang good book, My "Q-Jet bible"
I Suggest, you buy it and read it (several times)
The QuadraJet is hands down THE BEST best four barrel carburetor ever designed for the street, they are also one of the most complicated carbs ever built.

I Happen to have a Barker unwarping tool, this takes care of a lot of problems ...but you can't buy one anymore. You can send your carb out for "unwarping" though.
http://quadrajetcarburetors.com/unwarp-tool.html

Also, how are your throttle shaft bushings?
http://www.summitracing.com/parts/je...FQ4vaQodAx0AJw
Quadrajets are funny things, they often work fine ...until someone rebuilds them.

Re: Quadrajet or Quadra-throw out the dang window!!
 

Everything Greasey Harley said above. Once tuned right they are hard to beat. And get that Cliff book.

Re: Quadrajet or Quadra-throw out the dang window!!
 

Have you adjusted the choke? And the high idle? Both are cold start items. Q jets are great carbs.

Re: Quadrajet or Quadra-throw out the dang window!!
 

Choke adjustment and high idle have both been tried, in all sorts of combos, but with the same, or worse, results.

Re: Quadrajet or Quadra-throw out the dang window!!
 

A few of you have mentioned the throttle shaft. Before i dump another $100 on that, whats a good way to check them?

Re: Quadrajet or Quadra-throw out the dang window!!
 

Umm, timing tab? The small piece of metal by the harmonic balancer? This motor is kinda pieced together...suffice to say the Air Force doesn't throw money at it's Staff Sergeants. So, in the building phase of putting it together, i bolted the timing tab on.

Re: Quadrajet or Quadra-throw out the dang window!!
 

Could be the root of your problem!
After all, the old rule of thumb is 'Timing First, Carb second.
Best to prove your timing marks.
Use this as a guide.
http://www.crankshaftcoalition.com/w...op_dead_center

Re: Quadrajet or Quadra-throw out the dang window!!
 

You can wiggle the throttle and see if it wobbles . you can try sprayen a little water or starten fluid around the base of the carb and see what happens. if the shaft is loose the vacumm at idle should suck the stuff through

Re: Quadrajet or Quadra-throw out the dang window!!
 

Plus if it's the original 40 year old harmonic balancer, there is a chance that the rubber between the inertia ring and the hub is rotten or after eons of grease can slip. Throwing timing marks off. It can actually throw the marks off quite a bit!

Gary

Re: Quadrajet or Quadra-throw out the dang window!!
 

I apologize, its been a long day, but i recall setting the timing when adding all the gaskets to the new motor. We tore it down to the heads, block, and crank. The #1was at TDC, so, timing "shouldn't" the problem, but this truck is named Murphy for a reason.

Re: Quadrajet or Quadra-throw out the dang window!!
 

Im going to try wiggling my shaft tonight...wait...;)

Seriously though, im going to take a look, thanks frank!

Re: Quadrajet or Quadra-throw out the dang window!!
 

I see you live at close to 2000 feet elevation.
Try bumping your timing up to the 18 to 20 degree initial area.

Re: Quadrajet or Quadra-throw out the dang window!!
 

One of the first things you said was it might be a vacumm leak. If the throttle shaft is loose you have a vacuum leak. try some starting fluid around the shaft and see if the motor revs up. even carb with decent shaft bushings will respond a little . I love my vacuum gauge. if you have one and your motor is pretty stock that would indicate a manifold/intake leak by low vacuum reading.

Re: Quadrajet or Quadra-throw out the dang window!!
 

So, here's what I've discovered this evening after some wrenching...

Primary shaft has no wiggle. Solid as a rock...chevy reference...nothing...i digress

My secondary throttle shaft is indeed loose, good call all that mentioned. I can hear the secondary butterfly valves jingling away. I sprayed some carb cleaner on the base of the secondaries, next to the throttle linkage with no engine reaction, but its def loose. I didnt think a little wiggle could cause so many problems.

I also sprayed down around whole base of the carb with no effect as well.

So, from here I assume the only fix is to resleeve the openings that the throttle shaft sits in?

Frank, I assumed since the whole carb runs on a vacuum, it HAS to be a vacuum leak. i cant think of any other culprit. Good call sir, well played.

It was also mentioned to advance to timing for the altitude difference. I tried and the motor would spit and slug out when the throttle was applied in park. Thanks for the thought though.

Thank you all for the awesome wisdom and advice.

Re: Quadrajet or Quadra-throw out the dang window!!
 

I used to run quadrajets,but hard to get one rebuilt or buy a rebuilt that will work properly,now I buy Edelbrock performer carbs and run them on almost all of my rigs....they are easy to set up and are reliable,will set you back about $300.00 bucks, but well worth it, I get mine from Summit,they have the best price.....I only own pre-smog rigs...I live in Ca, and you have to smog anything 1976 and newer,these carbs aren't smog legal, but they work great...

Re: Quadrajet or Quadra-throw out the dang window!!
 

Maybe the carb cleaner isnt flameable. Try some into the air cleaner if there is vacuum leak at or below the butterflys u should notice something

Re: Quadrajet or Quadra-throw out the dang window!!
 

I did spray some into the carb while running to see the reaction, which was a drop in idle.

Re: Quadrajet or Quadra-throw out the dang window!!
 

If you need to get the truck moving and are going to use it as a daily driver. This is your best option ^^^^.
Sometimes when I get to a point with a engine problem (timing or fuel) and can't determine the cause, I will break out the ole Edelbrock and bolt it on to see what changes occur. They are easier to tune. But, remember a Edelbrock is a square bore and a Q-jet is a spread bore. You will need a adapter plate or a square bore intake manifold.

Re: Quadrajet or Quadra-throw out the dang window!!
 

I know I'm a relative newbie here..so for what its worth..I spent many months dialing in my Q-Jet.. for me it was the balance between the APT, Idle set screws and the timing. once I got them all in line its started and ran great every time.