I just checked the Summit site and they have their Summit racing brand reman carbs for 299.95 for a 305. Might be worth checking into.
Brian

 

Thanks for pointing out those on Summit. That is an option. But having lost a new engine once for mysterious reasons, which had a Pony Carbs new rebuilt 4100 on it, and having read how somebody found glass beads in theirs, I'm leery of factory rebuilt carbs. That $500 Pony Carbs 4100 was the only thing on the engine that I didn't KNOW what was inside. My bearings got wiped w/in a few days.

I think I will buy a used one, and take my time and learn the Q.J. one step at a time. That way it is not a mystery, and I know exactly what I have.

 

I'm very glad I bought this book by Cliff Ruggles, Rochester Quadrajet Carburetors. I always wanted to learn more about carbs. This is the perfect chance.

It seems these carbs are very adaptable. There is a small model that came on lower out put engines, v8's, with 1 3/32" primaries. The most common is a tad over 1 3/8".

I should have a lot of fun tuning it because one can adjust every aspect of the carb: the primary jets/m.rods and spring, and the secondary air valve spring, m.rods. I think the trick will be to get the coke bottle diameter secondaries to open w/o bogging the engine. Since there is no s. jets to dial down, it is going to be interesting to see if I can get the adjustment needed with m.rods and air flap spring adjustment. S. start to open at 2/3 throttle, and then the air flap controls when they kick in.

Primaries on the Autolite 4100 are 1 11/16" IIRC.
Edel. 1403 is larger.

 

F-250 restorer, I just got my new to me Offy 'C' this past weekend and dug out an old Q-jet that I have from a '72 350. My primaries are 1 3/8" and the tiolet bowl secondaries are 2 1/8", the outside total measurment of the secondary butterfies is 4 3/4". The hole in the intake is 3 3/8" sq.. Transdapt does make an adapter which I think is about $25.00. Good luck, can't wait to hear your results.
Brian

 

Hopefully I'll be able to find one of the QJ's with the smaller primaries. My book says they were calibrated for smaller engines. If not I'll go with one off a 305 or 307 and just dial it down. The book says one can make all the adjustments w/o pulling the carb. Nice. With the small bores the velocity of the air must be greatly increased, giving stronger response, signal.

Seeing that the secondary fuel nozzles are 1/4" tubes discharging fuel, controlled by the air flap, I'm thinking it is going to need to be dialed down a bit.

I'll also going to do a slight porting in the bores, removing factory casting seams, etc. All in all, I'm hoping for it to be nothing short of when they shift into warp drive in Star Trek.

Target carb seems to be 76--78 that has not had a mass rebuild, off a 305.

 

Prob. Friday I'll be hitting the 4 local yards since they are all having a 1/2 off sale. Heck, if I trip over a ZF sb, I may even buy that too. That means this weekend I should be stripping it down and sending for all the parts.

I can't wait to feel the toilet flusher secondary flaps open!

Harte3, you're THE carb guy on this forum. I'm wondering what you are thinking about all this ruckus.

 

I see Edelbrock has a sensor for reading the A/F ratio. I believe I will buy one and install it prior to the QJ.

 

Where are you, geographically? I've got a decent digital wide-band A/F meter I'd let you borrow. It's jittery/zeros when the AFR is way out of range but reads pretty steady between maybe 10:1 and 25:1

Another alternative would be to find a local shop that does dyno tuning and give them a crack at it.

 

F-250 restorer,
Think you're really on the right track, very intersted to see how this project turns out for you. The Q-jet was an often maligned carb despite the fact that it saw daily duty service in millions of vehicles. A few years ago Car Craft magazine did a write-up on the performance possibilities of the Q-jet and the main thrust of the article was that with proper maintenance and tuning it was a great way to go. keep us updated and post pics if you can.

 

I'm in So.Cal. Thanks for the offer, but I'll shop around and see what I can find. I know the auto swap meet is coming in a few weeks, so there must be something out there for a good price. I'll try to tune it by ear and v. gauge, then go from there.

If I can squeeze another couple of mpg out of a new carb. around town, it will be worth it. 'You have to love those tiny primaries.'

Regarding the Summit models: In my book it said to avoid the mass rebuilt QJ's. It seems they just shuffle the three components, air horn, base and bowl body, and create a generic one fits all model, and that makes it really difficult to recalibrate according to the numbers. But, now that I think about it, it would prob. be fine for this application.

I'm hitting the yards tomorrow to see what I can find.

 

You might check with Chuck at BC Broncos: B.C. Broncos - Early Bronco Carb/intake & connected things - B.C. Broncos He sells the Q-jet in three variations and a very good reputation for these carbs.

 

GFW--thanks for the tip.

I pulled one today from a 78 Chevy 3/4 ton van, with a sb. I am surprised to see that at only about 1/3 throttle the secondaries start to open. I know it is adjustable, but I simply thought it would be a bit later.



My book decodes the #'s as it being made on the 39th day of 79 for a Cal. Chevy with an auto. trans. Interesting that the factory installed permanet plugs over the idle mix screws to avoid tampering. However, finding one where they have not been removed is nearly impossible.

I want to set it up with the jets, m.rods, float level, of a 305. Does everyone think that would be a good starting point?

Another thing I'd like to get some feed back about is the throttle bore diameter. In the book it says the primaries are 1 7/32", which would be 1/32" smaller than 1 1/4". However, all the ones I have found, including this one, measure 1 11/32". Should I not be measuring at the throttle plates?

 

Rochester Quadrajet Tech Info - The Carburetor Doctor

 

Kevin: If I weren't so carb-poor now I would not hesitate to obtain a Qjet or other spread bore to use. I like the spread bore theory...small primaries and large, adjustable secondaries. I did have a spread bore Economizer Holley 4360 that AB used for a while but the darn thing lacked adjust-ability except for jet size and I traded it along with a couple of other carbs I had for a rebuild on my boat carb. I think the 305 starting point is as good as any.

 

After taking it apart I am surprised to find the primary jets so small, and the metering rods for the secondaries look like pregnant primary rods. They remind me of birthday candles!

Very interesting for a V8. Tiny pri. jets (smaller than anything in my Edelbrock 500 calibration kit) maybe .067--.071, with .041 m.rods. And yet with those drum stick secondary m.rods, they must plug up the fuel pretty well.