hastingsman

The gas prices are killing me! My '72 Cutlass Supreme drop-top is just sitting, waiting for something less than $4.45 per gallon. Is it feasible to disconnect the secondaries on the QJet temporarily so we can cruise once in a while? It's too pretty to be a dust collector!

Has anyone tried this? Or should I just plan on robbing my grandkids' college funds?

Thanks- Jon

jpc647

Could just not push the pedal down so hard, and the secondaries won't open?

1970supremevert

see attached prior posting...credit to original poster

https://classicoldsmobile.com/forums...g-picture.html

MDchanic

Yup.

Just put a block of wood under the gas pedal.

- Eric

oldcutlass

Jon, don't get me wrong and I apologize for being blunt. IMHO, if you don't have the money for the occasional cruise you need to sell the car and sit on the couch and watch the Velocity channel.

A 2V carb might gain you a couple of mpg but then there's the expense of that.

TripDeuces

I Rochester 2 BBL has bigger bores than a QJet primary. You'd actually lose mileage. I bet you could do 80-100 mph on the primary side of a QJet before the secondaries kicked in. Mileage is all about how you drive it. If you want better mileage get a vacuum gauge and always drive at the highest reading you can. I could get 19 mpg out of my 70 Toronado on the highway. But if you want to have fun then gas mileage shouldn't be your goal.

HonestDave

My experience as well. Qjets were always good for mileage if you babied them. Could be lots of other issues at play, though, to create bad mileage. I've had heat riser valves that didn't open fully, and other exhaust restrictions. Timing issues, brakes dragging, engine not at right temperature can cause inefficiencies. Even slipping trannies have caused me loss. It's really easy in this hectic world to miss some of the obvious culprits. I had a 64 Riv with bad mileage for six years. Wasn't until I sold it we noticed there wasn't even a thermostat in it. I changed the water pump when it went, but was so busy with my other cars, I never got to checking the simple things.

kitfoxdave

if you want MPG, get a Vespa... if you want FUN keep the OLDS! Don't let those dinosours die in vain!

dancutlass

$4,45 a gallon sounds like heaven to me! $8,50 here and I still enjoy driving my Olds..
In my opinion if you really love your car and you love driving in it, there's always a way to safe money elsewhere to drive your Olds once in a while

Doc350s

I'm with Dan. I pay about $7 a gallon up here in Canada and that's when it's cheaper.

HonestDave

My God !! I haven't done the math lately. It's $1.43 a litre, and I've been thinking around $5 a gallon. You're right, it's closer to $7, maybe more if you use premium. No wonder I'm spending so much at the gas stations.

bccan

I don't think you'll find any carb that will drop onto your engine & get better mileage than a Qjet on the primaries. Even most 2 barrels are apt to be worse for mileage.

Car will do nearly anything you want it to on primaries. I left my secondaries tied shut after some tuning & forgot about it, iirc car ran 13.2 @ 98 consistently w/ no change in normal driving.

Keep your foot out of it & you are driving a very precise 2 barrel that will be as miserly as your tune allows.

garys 68

Short of efi, the Qjet is probably the most efficient carb out there. The secondaries will not open until you push the pedal down far enough.
Check and make sure your ignition is working correctly, mechanical and vacuum advance. A shortened timing curve that has more initial advance can help a little bit.
Other than that, an OD trans is your best bet to increase hiway milage.

chadman

The best thing you can do for fuel economy is to get a wideband O2 gauge and tune your carb in. That and an adjustable vacuum advance canister.

MDchanic

Getting into this more deeply, I've often wondered about the practicality of substituting a much stronger spring on the secondaries, to make it obvious when I was getting into them, but I've never actually tried to do it.

- Eric

BILL DEMMER

with a '72 carb. you can fab up a piece to hold your secondary air valves closed-if you're serious about this. don't go bending on the existing lockout lever, after a couple of bends, the arm will break off and you'll be screwed.


bill

brown7373

Unless I missed it, what kind of mpg are you getting now?

BlackGold

Many of you are recommending that Hastingsman simply not step on the gas pedal hard enough to open the secondaries. What you may be missing is that this will also prevent him from fully using his primaries. The secondaries start opening at half-throttle on the primaries. The primaries don't fully open until the secondaries do as well -- at full pedal travel.

I like the idea of somehow preventing the secondary air valve from opening.

Let me rephrase that. I don't like the idea at all. But if someone wants to improve their gas mileage, that's probably a good way to do it.

garys 68

Not exactly... The circuits in a carb generally get progressively richer. Preventing the secondaries from opening and adding fuel will result in a lean condition on the primaries in heavy throttle. Would you suggest blocking the enrichment circuit (rods) and accelerator pump too?
A light foot and tuned carb/ignition will probably be a better approach.

hastingsman

Thank you, one and all, for the input. Just for the record, you couldn't offend me if you tried. I asked for ideas. I know the primaries on a Qjet are smaller than those of a 2 bbl., and that's why I was hoping to TEMPORARILY stop the secondaries from working. I don't want to change carbs.
At this point, I am getting 15 mpg highway with the rebuilt 350. Only changes on the rebuild are hardened seats and an RV cam, plus true dual exhaust. I think I will try to super-tune it, maybe install some split-fire plugs. They seemed to improve performance and mileage on a Firebird years ago.
I like the overdrive trans idea, but this one has a recent rebuild.
I am retired, singing the fixed income blues, but I simply can't see giving up the hobby. I'll play a bit and see what happens. -Jon

lshlsh2

What rear end ratio do you have? I'm sure someone has a 2.56 that they would let go cheap.

Larry

Nilsson

I get 9-10mpg, and I drive may be 3-4000 miles a year. You get 15 which I consider good mileage.

Napoleon1991

x2

BILL DEMMER

not in a quadrajet. the primaries will continue to function normally without the secondaries.
unless the original poster proves me wrong, i'm of the opinion that the secondaries won't flow any fuel without the venturi effect in the secondaries.


bill

oldcutlass

Here, I'll make you feel better, cruising around town I get 6mpg and run 93 octane. 15 is pretty good, I'd save my money on the split fires and run NGk, A/C, or Autolite. Give it a good tune and keep a fresh aircleaner on it. Make sure your tires are aired up, and you might squeeze a couple more MPG out of it.

hookem horns

Assume you have a daily driver other than the Olds. Think about what you can do to make that one sip gas so you can enjoy the Olds when you do take her out on the town. 15 mpg is pretty good for these old cars, and an occasional "italian tuneup" is good for the soul (the car and yours).

garys 68

15 is pretty good. I've got efi, a 4 speed, with 2.73 rear end and get low 20s for mpg. An OD trans is expensive, but 10 bolt rear ends are pretty cheap. You could swap out the rear for a lower ratio, but don't expect more than a few percent improvement.

455man

You might try some cold air induction like the 442's had under the bumpers. Headers would help get that exhaust out. I was able to get 20mpg with a 350 then 15 with my 455.

hastingsman

20 mpg would be GREAT! I'm going header hunting, and I already have a dual snorkel air cleaner from ebay installed. Just have to run the tubing. Thanks much- Jon

jensenracing77

This is not the same as blocking the secondaries and not what you are looking to do but this reminds me of what we did. Back in highschool a friend and I took a chevy 350 and stuck a freeze plug into one side of the dual plane manifold. We took out the spark plugs for the cylinders of that plane and drilled out the centers. we attached hoses to the plugs with the holes and ran them to a filter. It had more power than we thought it would. We ran it for a couple months and found it only got 1 to 2 MPG better in town but got 5 MPG better on the highway.

MDchanic

I've been busy, so not entirely focused on every post here, but I don't think I've seen any mention of the simplest way to disable the secondaries.

All QuadraJets have a secondary air valve lockout that prevents the secondary air valves from opening until the choke is completely off.

All you need to do is latch that little lug into the locked position, probably with a nylon wire tie in most cases, and your secondaries will not operate (carbs with priming jets located below the air valves may pull a little fuel from there - you'd have to check).

- Eric

Seff

A properly rebuilt and tuned Q-jet, un-castrated, should be in that vicinity with decent gears, careful driving, and a SBO. I did 21 with my setup. Highway, of course.

hastingsman

THAT'S what I'm talking about! I figured there had to be a simple temporary fix. I have enjoyed all the comments and suggestions, but this is what I originally wanted to know. Thanks. -Jon

bccan

Disabling the secondaries can be done simply by running a piece of wire (mig, mechanic's, etc) from the pivot arm on air valve shaft (rt rear of carb where vac pull off shaft connects)& tie it off on choke housing. Secondary throttle plates will operate mechanically but not enough air will flow through to draw fuel.

I tune Qjets for 12.5-12.8 WOT w/ cruise anywhere from 14.5-15.8 on PRIMARIES ONLY, basically through selection of primary jets & rods. It is like tuning a stand alone carb, for "normal" use the secondaries would then be untied & reactivated then carb tuned for WOT w/ 12.5-12.8 A/F by using secondary rods.

Only problem is you need an Air/Fuel wideband gauge to do it & probably some parts, ie a set or two of jets & maybe some rods. Primary piston might want 1 touch softer spring w/ cam in there. With headers & RV cam you may be a tad lean already unless float is heavy or overall tune is off.

Dilemma is spending money on rebuilding, recurving, retuning or spendin it driving around. Basically long or short term view. A dist recurve kit is in order (& cheap) either way but if this type of tuning is unrealistic for you, bump the timing up to the top of the pointer (10-14 degrees initial) & use a vac gauge to set idle screws fo max idle vac. You will feel a difference & possibly see a slight increase in mpg.

BILL DEMMER

as i stated a while back in this thread, lock out the secondary air valves with a fabbed piece of metal. your era of quadrajet has an air valve lockout lever, messing with it may cause the choke valve to operate improperly. mount a fabbed piece of metal to hold the air valves closed. you can attach it via one of the air horn to float bowl screws that are right in front of the leading edge of the secondary air valves. this way, the air valves will be held closed, very little(if any) fuel will flow from the secondary discharge nozzles OR the secondary accelerator pump ports, and the choke will function properly. later incarnations of the quadrajet had a secondary lockout lever that held the secondary throttle valves closed, not the secondary air valves.


bill

Aceshigh

Agreed.

Sell it, or put money into a 2004R overdrive transmission.
GM Overdrives came out in 1980 over 30 years ago now.......time to update the car.