425 Toronado Quadrajunk Replacement Recommendation

[streets]

Hi Guy's

It's been a while since I posted due too replacing the heads (ordered from afar,) gaskets and fuel pump, I am ready to get her back on the road, but need your expert opinions.

Mine is an original 1966 425 cu. in. 375 HP with a 4-barrel Quadrajet. Been there & done that on the rebuild (twice.) Idles great, but absolutley "No Power. :mad:

I have tried AFB's & Holleys, unfortunately they would not clear the hood (adapters) and admit I have no idea how many CFMs it takes to run it right (Guessing 700 :confused:

Being very close, please give me some suggestions that have worked for you.

As always, Thanks in advance.

Dave/streets

[joe_padavano]

Mine is an original 1966 425 cu. in. 375 HP with a 4-barrel Quadrajet. Been there & done that on the rebuild (twice.) Idles great, but absolutley "No Power. :mad:

Then you're doing something wrong. Sorry, but the Qjet is arguably the most sophisticated 4bbl ever created. Your car should have plenty of power if it's running correctly. Did you rebuild it yourself or have it done? My first guess is that the secondary air valves are not adjusted properly or the choke is not adjusted and thus locking them out.

[streets]

Hi Again Joe,

thanks for the quick reply. It started out as an Autozone off the shelf rebuild for about $250. When I found out there was a problem, I sent it into a professional rebuilder in Phoenix, another $150.

After the head gasket fiasco and the fuel pump problems resolved I am know in Illinois with no recourse

I would agree the choke and primary rods would have been the problem, but I had a friend of mine send them to me off a stock Toro. They were a little longer than the Autozone rebuild.It runs a tad better, but no where like it should.

Oh yea, another issue is this carb has no numbers on it.-Just want to give up and get it right.

[carbking]

The Rochester Q-Jet is a wonderful carburetor; however the pre-1968 models did have some "teething" issues.

Two such issues on your carb, unless corrected, would be the early "umbrella" fuel valve (would be replaced by any professional with the conventional type) and the internal dashpot which worked (or didn't!) in conjunction with the secondary airvalve.

Prior to the 1968 model year, Rochester Quadrajets were identified by a round tag pressed into a round hole on the drivers side of the center casting.

Since the auto choke is of the "divorced" or "remote" type, the thickness of the mounting gasket will have an effect on the operation of the choke. The choke rod is adjusted by bending. The choke plate should just TOUCH closed with a cold engine and the ambient temperature between 65 and 70 degrees F. Heat from the running engine warms the coil, allowing it to relax its tension. This allows a functioning "choke pull off" to open the choke. The choke plate or "butterfly" should be in the fully open position (completely vertical) within 3~8 minutes after starting, depending on the ambient temperature, and whether the car is parked or driving.

Failure of a correct adjustment on either the choke or the secondary airvalve will result in a tremendous loss of power.

Before even considering sending the carb somewhere else, or worse, replacing it with a different unit; I would highly suggest making sure of correct adjustment. If nothing else, it is certainly cheaper.

And remember, 90 plus percent of all "carburetor" issues turn out to be ignition!!!

Jon.

[Guest Twilight Fenrir]

You know, I'm having a similiar issue with my '66 Toro, with a non-orriginal Q-jet, but it's still from a '66 Oldsmobile. I just did the rebuild myself with a kit I got from Fusick. It definitely runs better, but it still has no power. It idles smooth, and seems to rev smoothly. It has some decent acceleration, but nowhere near where it should. I can't even burn rubber, and these cars are famous for that.

The Dashpot was completely siezed inside its chamber. I had to heat it with a torch for 10 minutes to get it out, and finally did. Sanded and made it all move nicely. I had hoped that was all that was keeping the beast caged, but alas, no significant change.

I fiddled with the choke to try and tune it, but the procedure requires three hands, and I don't have that It is releasing the lockout however. And when I grab the secondary throttle linkage and pull on that under the hood... the baby roars

What they say is true though, Q-jets are some of the very best carburetors made. They are hands down the most efficient, and properly tuned, can pump out as much, if not more power than the Holleys, Edelbrocks, etc... The catch is getting them tuned. And our early units lack alot of the small changes that were made that made them the best.

If you're really set on replacing them, get one from a few years later. I think after '68 most of the most significant changes were in place. And I believe by about '75 they were as good as they were going to get. Shortly afterwards they started introducing the electronically regulated Q-jets. Which, while actually being more efficient, were limited for their output. Plus... y'know, they had computers... which is a word that should never be said near our classic cars.

And remember, 90 plus percent of all "carburetor" issues turn out to be ignition!!!

I've heard this, and was wondering exactly what it pertains to... Are you talking about timing issues? Or damaged/worn hardware? I replaced the points with an electronic conversion, and put in a new high output coil. Got new plugs, and wires... The cap and rotor are both probably from 1966 though.

I went to set the base timing, and the service manual says to do it at 850 rpm's.... How do I know the RPm's? There's no tachometer. I just kinda figured 850 should be right about idle, and set it at 7.5 above TDC like the book said.

Edited June 2, 2011 by Twilight Fenrir (see edit history)

[Guest Julian]

the Qjet is arguably the most sophisticated 4bbl ever created. Your car should have plenty of power if it's running correctly.

I agree.. I have messed with quads since the early 70s and have never had an issue with one. I have rebuilt them myself (NOT an expert---but good enough) and not had any problems with them performing...ditto for the 4GC that I encountered over the winter (once I figured it out)

[Guest]

Then you're doing something wrong. Sorry, but the Qjet is arguably the most sophisticated 4bbl ever created. Your car should have plenty of power if it's running correctly. Did you rebuild it yourself or have it done? My first guess is that the secondary air valves are not adjusted properly or the choke is not adjusted and thus locking them out.

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I'm with Joe here, I suspect something wrong with the secondary air flap operation or moreover non-operation, although my street 455 Pontiac will smoke the hides with the secondary air flap linkage locked out.

IMP best 4bbl made. I even use one in road racing and G/Touring.

[carbking]

I would highly suggest to anyone tuning their older vehicle; that the very first tool one should buy after the screwdriver and pliers is a dwell/tach meter.

Having said that; as the electronic conversions are banned from my personal vehicles, or any vehicles that I will work on, I have NO idea if the dwell/tach's are compatible with electronic conversions. Possibly some electronics guru will chime in.

However, with the old points/condenser system, a dwell/tach is an extremely useful tool (OK, so it probably won't work with magnetos either).

There are a veritable host of issues that can go wrong with an ignition system, both self-inflicted and created by installing cheap aftermarket replacement parts (I am referring here to non-original brands, not the conversion).

Jon.

[Guest]

I would highly suggest to anyone tuning their older vehicle; that the very first tool one should buy after the screwdriver and pliers is a dwell/tach meter.

Having said that; as the electronic conversions are banned from my personal vehicles, or any vehicles that I will work on, I have NO idea if the dwell/tach's are compatible with electronic conversions. Possibly some electronics guru will chime in.

Jon.

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Jon, they are. On the side of a GM HEI where harness connects, there is a spade that says tach. The only thing wrong with HEI is people forget to service the distributor- lubricating the advance weights, making sure the vacuum advance works, looking at cap & rotor and the MOST important, taking the module out once a year cleaning the bottom of it and the plate it mounts to and applying dielectric grease to the plate and the module and remounting. If you do that a module will last a very long time if not the average life of a car.

[Guest Twilight Fenrir]

Hahaha, I just figured out what's wrong with mine... It's really obvious, I kinda feel silly. The rod attatched to the transmission pitch contoller is hitting its stop before my primaries even finish opening! No wonder I got no power. Might want to check yours Street.

[joe_padavano]

I would highly suggest to anyone tuning their older vehicle; that the very first tool one should buy after the screwdriver and pliers is a dwell/tach meter.

Actually, the first "tool" anyone should buy is a factory service manual - even BEFORE the screwdriver and pliers.

[carbking]

Actually, the first "tool" anyone should buy is a factory service manual - even BEFORE the screwdriver and pliers.

Agree! Absolutely NO argument on this; not a bad idea to buy the shop manual BEFORE one buys the car!

Jon.