Based on your picture, it looks like that electric device is just an idle compensator. It may have been used to keep the idle higher when A/C was on, or for some emissions reason. Electronic quadrajets usually have a wiring connector on the very top of the carburetor, and the connector housing is blue.

Based on my notes, the accelerator pump lever goes in the 2nd hole, on the far end.

Find the number on the side of your Quadrajet, which might be formatted like this 7045583 (up to about '75), or on later ones it will be a longer number like this 17080213. Look up that number to find the right rebuild kits, parts diagram, tune-up specs, etc.

Bruce

 

It was also used as an anti-diesel solenoid.
When you shut off the motor the solenoid plunger retracted and the throttle closed all the way.

 

^^^THIS. All this is is a solenoid. Different years used this in different ways, but all it does is kick up the throttle. As noted, some years use this to increase idle speed when a load like A/C is turned on. Other years used this to hold the curb idle speed under normal conditions and turned it off when the ignition was turned off to suppress dieseling.

 

I used a 1967-1972 Rochester Q-jet and a 1967 intake manifold on my 1962 Chevrolet with a 1968 350 CI engine. The 1967-1972 Q-jets are basic non-smog carburetors. You can distinguish the 1967-1972 Q-jets from the 1973-and later Q-jets by the base gasket.

I purchased the 1967 Q-jet from Chief Auto Supply. Runs perfect after I snipped off and removed the secondary air valve detent lever with a pair of dikes. That allows the air valve to fully open.

 

The idle speed solenoid was used on Pontiac Ram Air IV Engines because of the 1000 RPM idle speed required with the RA-IV camshaft. The idle speed solenoid completely closed the primary throttle blades of the Q-jet when the ignition key was turned to the OFF position, thus preventing engine “run on”.

I have a idle speed solenoid on the 1967 Rochester (Pontiac) 750 CFM Q-jet on my 1962 Chevrolet with a 1968 350 CI engine with a L-79 camshaft. I tapped into the coil primary wire from the starter solenoid to the stock coil primary terminal in order to power the idle speed solenoid and hid the wire in the wiring harness. Works great with the Pertronix Stock Look distributor.

Rebuilt Rochester Q-jet #7027263 from Chief Auto Supply...... $250.

 

I purchased that Q-jet five years ago. Now that particular Q-jet is selling for $1000 to $1400 on E-bay. It originally was for a 1967-1969 Firebird 400.

The secondary air valve lock-out tab on the 1967-1969 Pontiac Firebird 400 #7027263 Q-jet was to reduce the factory advertised horsepower rating to 345 HP so not to conflict with the factory horsepower rating of the 1967-1969 Chevrolet SS 396 with 350 HP.

Remove the secondary lock out tab on the 1967-1969 Pontiac Firebird 400 Q-jet and you will gain 40 horsepower at WOT.

 

They got you straight on the solenoid, but the accelerator pump hole I have always used is the inner hole. It will give a bigger pump shot. You can try the outer hole, but if it stumbles going off idle, you know to put it in the inner hole. I tried it once and that's exactly what it did and I did.

 

The verbage is still a little ambiguous, the hole nearest to the pivot point of the lever will give the biggest shot.
.

 

Here is the numbers on it. Like I said I have always ran it without a wire going to it and never had any issues but if it's something I should be using or if it will help in anyway I'd like to use it. If not it looks like 💩 I take it that a 12v accessory wire will do the trick.

 

The number you want to look up for parts and rebuild kits is 17059207, which should be a 1979 Quadrajet used in a Chevrolet. The "1969" below it is not a manufacture date, so don't get confused.

This is a relatively new Quadrajet that should be a good start for your engine build-up. You need to first ensure the basic carburetor is working right, and then look at what performance tweaks you can make to get it working a little better for your application. Most of these Quadrajets will flow up to about 750 CFM, but as MouseFink mentioned, sometimes they were modified by GM to reduce flow in certain vehicle applications.

I suggest you buy the Cliff Ruggles book on Quadrajets and start reading through it. However, the book can get confusing because it covers all the Quadrajet models. For example, he may suggest an improvement for one carb model that does not even apply to your carburetor, so read carefully. You can also call his shop, or post to his online forum and he will tell you what rebuild kit to use, or what performance tweaks would make sense.

If that plunger is just an idle solenoid, it probably doesn't even need to be connected unless you have A/C.

Bruce

 

If it was not for the Q-jet secondary air-valve limit tab, a 1967-1970 Firebird 400 would have been in the same auto insurance rate category as a Corvette, based on horsepower to weight ratio.

 

Yeah it works great. Always did. Haven't used it in 8 years though that's why I rebuilt it. It came on my 79 el camino ss. Thanks for all the help

 

Guys I need a cheap carb adapter to fit this Q-jet on a square bore intake. I know they aren't worth a darn. I dont care. I need to get this fired up, broke in, put in the car before it gets to cold then I'll buy me a carb next spring. I have a dual plane intake, dont know if that matters but like I said I just need to break the motor in and get it in the car. Thanks

 

You use the same adapter that is used to adapt a squarebore carb to a spreadbore intake...you just flip it over and put the captured bolts/studs in the opposite hole pattern.
Commonly used to put a 4150/4160 squarebore Holley on a Q-Jet intake.

This is from Holley's site, but at just 3/4" thick it might hang up the big Q-jet secondary's and wedge them open, so check any adapter you use in this direction for WOT clearance and grind on the adapter if needed. You might want to search for one 1" or thicker.
https://www.holley.com/products/fuel_systems/carburetor_components/adapters_and_spacers/parts/1932

 

Check the throttle plate movement carefully for binding if you use an adapter. I've had issues with adapters being "just right" to fit the plates, so if the adapter or carb are bolted on just a little bit off you will get binding of the plates.

Bruce

 

Thanks for the info. For 3 weeks now I've been looking at adapters and a guy at oriellys showed me the same chart in the link above but it said square bore carb to spread bore intake. That's why I never got that. But now I know. Thanks again and oriellys had that exact adapter in stock for 20 bucks. There was also an edelbrock adapter there also but it was more like a 4 hole tapered spacer. 1 inch thick. It was only 5 bucks more. Could use that and flip it over. I'm sure I'd have to make sure there is no binding as well.

 

Reason it's not listed as "spreadbore carb to squarebore intake" is that virtually no one is trying to do that combination, you are in a tiny minority of users in that direction.

30ish years ago when everything 4 barrel from GM had QuadraJets there were at least 10 companies all making a version of this adapter, and it was almost always listed to go both ways....today QuadrJet users are just a small minority, it hasn't been installed on a new production vehicle since 1987...30 years ago LOL

just a funny history lesson...

 

Its crazy to think its been that long ago. Time flys. And I also figured that out that hardly anyone is doing this qjet/manifold setup. Figured that just by trying to find one. The plan is to get me a new carb it's just I have $4000 in this sbc and money is tight right now. So before it gets to like 0 degrees outside I'd like to get it in the old elky. But then again I almost want to wait and go ahead and swap those vortec heads with the afr 195cc street/strip heads I originally planned on getting.

 

Maybe it's just time to button it up for the winter rather than trying to rush a quick start then leave it sit with combustion products in and on the internals for the next 3 to 5 months. That will buy you time to save up for a square bore carb or a replacement intake for the Q-Jet which ever way you decide to go with that and the replacement heads. That, also, gets around having to fill it with coolant that only has to be drained for these swaps along with the wasting of the engine oil that entails. It, also, pushes any start up problems off till better weather and more time to work them through instead of suffering through a panic to beat winter's icy hand.

Bogie

 

I'm going to go ahead get this fired up and broke in but leave it on the stand in the basement for the winter. That way if something goes wrong I'll have something to work on and have it ready by spring.

 

Ok, after having issues with the q jet on a previous motor I rebuilt it and I'm still having issues with it at idle on this motor. So decided it's time to toss it aside. What carb do you all recommend. Not sure if i posted engine specs so I'll do it again.

Stroke:*3.750
Disp. @ .030:*383
Rod Length:*5.700
Pistons:*-12cc Flat Top

Xtreme Energy XE274H Hydraulic Flat*

Operating Range: 1800-6000 RPM

Duration Advertised: 274° Intake / 286° Exhaust

Duration @ .050'' Lift: 230° Intake / 236° Exhaust

Valve Lift w/1.5 Rockers:. 490'' Intake / .490'' Exhaust

Lobe Separation Angle: 110°

906 Vortec Heads 1.94/1.50 valves

Summit dual plane intake

1 5/8 headers

 

"Desktop dyno says 412HP at 5400, 410 HP at 5300 and 5500 rpm,...Torque is 438-440 ft.lbs between 4000 and 4500 rpm, and is making 400 lt.lbs by 2800 rpm" courtesy of ericnova72
Not sure if this is useful info for carb selection but just in case

 

780 Quick Fuel Part# HR-780-VS or Part# SS-780-VS. Can't go wrong with either of these carbs on a 383. These two vac secondary carbs have adjustable IFRs and PVCRs. Both have screw in air bleeds on both ends and 4-corner idle. If you're going to spend the money for a new carb, get a good one. Leave the double pumpers for very light vehicles with higher stall converters.


I have the SS830 on mine and I love it.

 

If your going to go with a 750 plus cfm carb vacuum secondary then I recommend the quick fuel brawler which is identical to the hotrod series carb and has all the same exact features but is way less in price and they have a sale on them right now and for just $298 and it is all cast though but its a great deal and its four corner idle etc.

https://www.holley.com/products/fuel_systems/carburetors/brawler/diecast/parts/BR-67258

 

That's a really good deal! They say 4 corner idle on mechanical secondaries but show idle screws on secondary side in photo of vacuum secondary carb.

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I got this off of speedway motors website. Also have read it in a magazine article

The formula for calculating how much CFM (cubic feet per minute) an engine requires is: CFM = Cubic Inches x RPM x Volumetric Efficiency ÷ 3456.

Any ordinary stock engine will have a volumetric efficiency of about 80%. Most rebuilt street engines with average bolt-ons have a volumetric efficiency of about 85%, while race engines can range from 95% up to 110%.

If I use this method I come up with:

(1) 383c.i. x 5500rpm = 2106500

(2) 2106500 x .90(volumetric efficiency) = 1895850

(3) 1895850 ÷ 3456 = 548CFM

Now almost every forum I read most guys are running around a 750 cfm carb with a similar setup as mine. So is this formula bull**** or is everyone else just running to much cfm. One could argue that my VE should be calculated lower than 90% also which would drop the cfm more. 85% VE would put me at 518cfm.

750 sounds better, 550 sounds to low, 650 seems right but I'm no expert on carbs. This motor will be seeing high rpms probably everytime I go out for a cruise

 

Vacuum secondary carb adjusts itself to engine needs.

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If you don't feel you need the full on race type adjustability of the carbs mentioned, there is the QuickFuel Slayer 750 Vacuum secondary. It has a good portion of the adjustable features but not all of them, just the most commonly used .

https://www.holley.com/products/fuel_systems/carburetors/quick_fuel/slayer_series/parts/SL-750-VS.

it's on sale now too.

 

Formula is very conservative, as they don't want to advise something bigger and then get low rpm drivability complaints from guys with more stockish engines.....Its also based around the 4 barrel rating system of 1.5 inches of mercury of vacuum occurring at WOT....if you are pulling that much vacuum at WOT then the carb is too much of a restriction for best power.

A good hot motored ride you really don't want to even see 1/2" of vacuum at WOT.

For hot street , street/strip and drag use you practically have to add 200 cfm to the results of the math formula.

On a dual plane intake, the carb seems smaller to the engine r than it really ism due to the divided plenum.

Modifications like you've got, a 650 Double Pumper would work, but a 750 Vacuum Secondary will run as a good or better, and still not give any low end away to the smaller carb... while it will pull away in the upper rpm range. Plus it won't limit power if you make future modifications like a very good flowing cylinder head