This post is primarily for informational purposes. I have done these mods, and they do work, but my combination was specific. Your results may vary! Modifying carbs is fun, but can be easily destructive. Have a parts carb handy! Modify the part on that one first if you are going to, then transfer it to the other carb. Most mods are not reversable! If you don't like it, you may be stuck with it. If you drill into a passage and go through, you may ruin your carb! Plan carefully. Mount things in a vise or clamp to a drill press to drill. By all means, get Doug Roe's book on Rochester Carburators. It is a MUST HAVE before you start to modify your carb.

Something I did on my 350 Olds, which was using a 307 ECM. Tune the Q-JET for WOT power. I found best power to be around .85 to .88v on the O2 sensor at WOT. I found that .92 and higher just seemed too rich and did nothing for power. Lower (leaner) voltage seemed to have a more crisp WOT power.
To do this you will need to connect a wire to the O2 sensor, and run it into the car, OR connect it to the O2 input at the ECM. Use the ECM ground.
Connect to a digital volt meter. Select the 2v scale. With engine cold, you will see a fixed voltage on the O2. Once you pass 3.5 minutes time since cold start, it will be fluxuating up and down fiarly quickly. But a stab at WOT will show it stops fluxating and goes to a fixed voltage. This is what the secondaries are flowing, as ECM cannot control the secondaries.

I have a boatload of metering rods that I used to tweak with. Honestly, I had ended up with a fairly fat rod on the secondaries, with the air flow of the secondaries allowed to go to WOT (yes boys and girls, the carb on a 307 WILL flow 800 CFM...) The carb is a vacuum secondary, so it will only flow what is needed. So let it have what it wants.
I used a H or earlier hangar, as I had that too. The rare and elusive "A" hangar was factory on the 1986 Astro van w/4.3 V6 if you are ever looking for one...

Ok, some other mods that I did....
Careful tweaks of the carb settings to 1985 HO 307 "9" specs gave great drivability. I also drilled 4 tiny holes in the secondary fuel feed tubes to allow for faster fuel pickup (as per Doug Roe's Q-Jet book, page 125), and the secondary feed holes moved to the above the secondary air doors (P.124).
I also drove down the internal secondary air bleeds to the recommended 1in depth to reduce the passage restriction when assembled (factory is 1.25", which is too far down).

I modified the accelerator pump circuit, (feared by some for loss of fuel economy, but I never lost any, and drivability was enhanced) bu shortening the fuel pump rod so that the pump would be higher in the bore, but not high enough that it would cavitate and allow fuel to pass the seal. If you need more seal thickness, the 2GC accelerator pump seal can be used. I actually cut around 3/16" of an inch off of the pump to get it in the right place in the bore! Many aftermarket pumps are pretty sloppily made. Heavy cars need more pump shot. This can also be accomplished very well with a new accelerator pump arm linkage that is much longer and have a new bend in it to allow for adjustability. I saw this on a 68 Ram Air II Firebird that ran 12.2's in SS/F. I also recommend finding a early 80's E4MC/E4ME carb that has the accelerator pump arm with the linkage closer to the piviot point. If yours is out at the end, you can drill a new hole farther in and relocate the arm location. You will need to readjust TPS when you have the pump dialed in.

Next I tweaked the point when the secondary throttle plates start to open. This is an area to be VERY careful, going a little too far here can make the secondaries open too early causing drivability problems (you don't want to cuise on the secondaries do you?. You need to carfully time this opening point with the ECM going into WOT mode. And you must make sure the secondary throttle blades do not open too far or not far enough, as this can lead to lean cyls, not even fuel distribution in the intake. You must get the book for these mods.

Also, as many have posted here on this site, adj the secondary opening rate. This has a big effect on the car. With this and the other mods listed above, the Q-Jet will be a very smooth, very powerful carbonator that will rival EFI for response and power.
Float level. 307 "Y" engines have a low float position compard to the "9" engine. I like the "9" position, as it decreases the transition times, so there is less a delay for the fuel to start moving. Too high can cause fuel to move when it is not ready to. A little goes a long way here.

Nice! I'm impressed with your knowledge of the Q-Jet. Not many people would do what you have done. Tell me, did you ever try re-jetting the primaries? I've had so good success with it on several cars. The only drawback is occassionally, you can end up with an intermittent code 45 at cruising speeds. As soon as you vary the engine speed (throttle angle), the light goes out so it's not a big deal, and this only happens on SOME applications. This gives you a noticably stronger bottom and mid-range.

Ahhhhhhh, fond memories of the Q Jet..............................20 years ago! Thank goodness for fuel injection. What NODIH is describing is something that should be approached with caution to some extent. The swapping of carb parts for different linkage/actuation ratios, modifiing parts by removal/adding material, drilling or relocating emulsion tubes, etc., is a tricky thing. I couldn't help but notice that NODIH mentions what I think is a NHRA class SS/F, so he certainly has this knowledge. It is great fun to tweak the Q Jet, which when correctly modified will perform as well if not outperform any carb out there, yet it is a tedious effort to get the right combination as NODIH eludes to. Such as "hangers" and the like, add in that you may be under the control of an ECU and your path to success may be even more difficult. I'm not saying don't attempt this sort of thing, hell, it's fun. Just be prepared to learn alot of new things and never forget that with every action there is an equal and opposite reaction. Oh, and I'm sure NODIH will probably agree, never drill into a Zinc body carb that is not bolted down, it will grab and do all sorts of things you will not like!
lry99eldo

I never did rejet it, as the O2 sensor indicated that it was fine with the stock jetting. There is actually quite a bit of bandwidth there for the ECM to play with to keep fuel mix at 14.7. I had a 77 350 Olds, SSI 204/214 cam, 3A heads (8:1 compression, too low for that cam) with the 85 ECM, an 82 Q-Jet E4MC from a 307, with an 82-83 aluminum intake from a 307 Wagon (took me 15 min to yank it in a boneyard, I was on a trip coming from St. Louis to Wisconsin and stopped at a great boneyard next to the racetrack in Madison, Il "Speedway" is the name of the place. It used to be awesome, lots and lots of older cars, a friend of mine picked up a 370 Pontiac that I found in there, I have seen 371 Olds V8's too), running a 77 drivers side manifold, and a 80 260 passenger side (older style, O2 in different place than later revisions).

I just keet playing with info I learned from Dougs book, I came up with very little on my own, just applied what I learned and experimented with. Although he didn't talk too much on the E4M series, I did apply much of what he did have for it. It was my daily driver, so I did have to keep it running good. I was that nut case who didn't have a scan tool, so I had an old power supply wiring harness running from all the sensors I wanted to monitor under the hood to the passenger compartment with a slew of multimeters I borrowed from work. I had a lot of my notes on my work there on the http://www.oldsgmail.com/ site, but they appear to be gone. I'll ask around if they are still there. That is where I started to tune for wide open power. And watching things under the hood, like M/C solenoid, O2, CTS, TCC, etc It really got interesting to see some of the relationships fall into place.

If you need more adjustability in the carb, you do need to step to the older version, that has an adjsutable upper stop, the later ones have only a lower stop adj to keep people from messing with it. Most 84 and older were adjustable

Nice! I'm impressed with your knowledge of the Q-Jet. Not many people would do what you have done. Tell me, did you ever try re-jetting the primaries? I've had so good success with it on several cars. The only drawback is occassionally, you can end up with an intermittent code 45 at cruising speeds. As soon as you vary the engine speed (throttle angle), the light goes out so it's not a big deal, and this only happens on SOME applications. This gives you a noticably stronger bottom and mid-range.

By all means lry99eldo, I should have listed a disclaimer on this first, I will go back and edit that. Use caution! These are not "make your 307 a 12 second car" mods. They were done in the interest of drivability (what I have studied personally) for your car. If it is running as it should, and no "issues" leave it alone, they aren't trivial mods to do, they can wreck a good carb if you are not careful. I had 2 Q-Jets to use, so I had spare parts, and yes, I did damage the pickup tubes, they are tough to drill into.

The details on the car for SS/F was a 68 Bird w/Ram Air II 400, and he ran low 12's with a Q-Jet. Instead of modifying the accelerator pump circuit as Doug Roe did, he took a different approach, he created a new linkage, that was 1-2 inches longer, and built in a couple good bends to take up the slack, then you just adjusted the linkage to position the pump exactly where you need it for the pump shot/duration that you desire by positioning the pump up or down in the bore. Slick idea. I didn't have a linkage to do it with, so I redrilled mine. I love to see what the SS guys do to make the car run and run fast within the rules of "stock". There is a guy with an 80 Turbo T/A running low 12's to high 11's. "stock"! Mine ran 14.21@97 mph. Fast for a pathetic 301. I didn't do much at all to that carb. I still have a few stacks of Q-Jets in the basement. A parts E4MC, a 76 500 carb with 60K miles on it, 301 Turbo, a couple GM school carbs (an interesting one there, one had remote vacuum to the power piston like the 301 Turbo carb, only with a chevy style float bowl, not sure of application), my original 69 428 HO carb from my 70 455 from a Hearse (commerical chassis may have got an early 455 with a late 428 carb??)

My goal was to make the mods happy with the ECM. And that it was. It took time and patience. I love to tweak! Unfortunately I sold the car, and it got sold again, and that owner screwed up the engine, then he sold it, and that kid didn't know much and his mother in law wanted that old car gone, so it got junked. I never got a chance to get it. I will see if the carb got saved, but I doubt it. I think at least he saved the dual snorkel air cleaner. It didn't fit on my T/A, else I would have kept it.

Take an engineering approach to it, log all changes and mods. Theorize what you are going to do and why. Then mod. I was trying to get secondaries to work better and smoother. Primaries were ECM controlled and within GM specs, so I left them alone. Just did super accurate adjustments on rich and lean stops, float, etc. It takes time, do it right and it will be very rewarding.

Heck, maybe I will have to run the Fleetwood in SS! That would be a blast!


Ahhhhhhh, fond memories of the Q Jet..............................20 years ago! Thank goodness for fuel injection. What NODIH is describing is something that should be approached with caution to some extent. The swapping of carb parts for different linkage/actuation ratios, modifiing parts by removal/adding material, drilling or relocating emulsion tubes, etc., is a tricky thing. I couldn't help but notice that NODIH mentions what I think is a NHRA class SS/F, so he certainly has this knowledge. It is great fun to tweak the Q Jet, which when correctly modified will perform as well if not outperform any carb out there, yet it is a tedious effort to get the right combination as NODIH eludes to. Such as "hangers" and the like, add in that you may be under the control of an ECU and your path to success may be even more difficult. I'm not saying don't attempt this sort of thing, hell, it's fun. Just be prepared to learn alot of new things and never forget that with every action there is an equal and opposite reaction. Oh, and I'm sure NODIH will probably agree, never drill into a Zinc body carb that is not bolted down, it will grab and do all sorts of things you will not like!
lry99eldo

I never did drill into the carb body, I got nervous there. I can see it catching and spinning for sure. The big D Bodies probably would respond to some of the mods, as they are heavy and the accelerator circuit is often set weak on the 307. Probably for emissions to reduce the shot of fuel that the ECM might not be able to respond fast enough to.

NODIH, that "caution" edit hits it perfectly, thanks.
lry99eldo