KQQLCAT

I have a 1962 Olds Rochestor 4GC that is giving me problems. A little history. I am converting my 61 Olds 88 394 from a two barrel to 4 barrel. It ran fine with the 2 barrel but I had to do a valve job and since I had all the parts to convert it and had it all apart I figured I would change it out. I had a local carb rebuilder (The Carburetor Shop) restore/rebuild this carb. It looks great but It has 2 problems. It has a major bog when I touch the accelerator and if I get into the secondaries and go to idle it has a real rough idle untill I pump the accelerator a couple times then it idles smooth again. I plan on taking this back to the rebuilder but I want some ideas to tell him to look at.

Thanks for any advice you can give,
Pat

jrzybob442

Believe it or not the 4GC has an air valve wrap just like the Quadrajet. My guess is that it is not set.

The following should help this is contributing to both problems.

This is how to set the wrap from my Olds Performance Manual:

Step Four – Set the Auxiliary Throttle Valve. No matter what you did in the way of rebuilding or modifying – if the Auxiliary Throttle Valve spring wrap is not set correctly, the carburetor will either sag or bog or – most likely -accelerate like a lazy 2 barrel car. The instructions regarding "clock-wise" or "counter-clockwise" assumes that the Auxiliary Throttle Valve is out of the carb and is sitting on the workbench as shown in the picture.
ü First, insert a small screwdriver into the screw slot on the side of the valve as shown. (See arrow on the bottom left in the picture opposite).
ü Note the location of the screw head in relation to the Throttle.
ü Then insert an Allen wrench in the hole on the valve throttle body and loosen the Allen lock screw, while keeping the screwdriver steady. (See arrow on the top right in the picture attached).








ü Turn the screwdriver clockwise to free the Auxiliary Throttle Valve (the butterflies should flop back and forth freely). Tighten the Allen screw momentarily set the tension and wiggle the butterflies to ensure that the Auxiliary Throttle Valve is loose.
Now return the screw driver to the slot, then loosen the Allen Screw and turn the screwdriver counter clockwise until the Air Valve just barely closes. (Zero tension). Note the position of the screwdriver. This is your starting


Bob G

jrzybob442

The system cut off the message - here is the rest of the procedure

ü Tighten the Allen screw and make a note of the position for future reference.
ü The proper Auxiliary Throttle Setting is the additional tension BEYOND the position you just marked (usually ¼ and less than ½ turn counter-clockwise). Remember to tighten the Allen Screw after each adjustment.
ü NEVER TIGHTEN the spring screw more than 1 turn. This will stretch the spring and make future adjustment impossible.
Step Five – Test Effect of Adjustments to the Auxiliary Throttle Valve. Accelerate the car @ WOT from a start with the wrap at ½ turn, which we will call the "stock" position. This is your baseline. Now:
ü Decrease the tension in 1/8 turn steps until bog is detected. This usually occurs by only a ¼ turn. If bog is felt immediately, (first run; tighten 1/8 turn). Automatic transmission cars may need more tension than manual transmission cars.
ü After you have reached your maximum tension, change your Secondary Jets. Try going richer first, but don't be afraid to go one step leaner too.
ü When you have base-lined to the best set of Secondary Jets, try readjusting the wrap in 1/8 turns. Throttle valve wrap changes the point at which the secondary mixture is fed to the carb - in the low and mid range of engine speed, so this is why you need to reset the wrap after you've changed the Jets.
If you are unsure as to the result, go back to the original ½ wrap and try one step in richer Jets and work from there.

KQQLCAT

It looks like from a parts break down that the carb has to be disassembled to get at the part to adjust right? If so I will give this info to the rebuilder.
Thanks
Pat

jrzybob442

Yes. You have to take the throttle body away from the float bowl, though if you have the carb off the car it is not that hard.

The problem will be the setting and without testing - it may still be too loose or too tight. Whoever sets it, opt for a bit tight over loose, so I would suggest at least 7/16s turn tight.

The problem is that even the slightest bit too tight or loose will result in crappy performance, but loose is worse than tight.

jrzybob442

We don't have the 1962 service Manual on Wild About Cars yest, but we do have the 1964 manual - which is the same for the 4GC. You can look thru it (and download it)and decide if this is over your head.

http://wildaboutcarsonline.com/membe...Sections_4.pdf


www.wildaboutcars.com It's free.

rocketraider

Pat, didn't you swap out the SlimJim for a THM in this car? If so, you could put on about any Edelbrock or small pattern Holley and get rid of the 4GC since you no longer have to fool with TV rod adjustments.

In spite of its small airflow rating, the 4GC is a good carb when it's right. It is a true POS when it's not. Bob G's air valve setting procedure should help, but these things are finicky about float bowl-to-throttle plate gaskets too. Wrong one for application will make them do strange things- different carbs use different air or vacuum bleed passages on this gasket.

Check the vacuum advance canister too. One of my Starfires had a bad one that made its 4GC bog badly.

jrzybob442

Along those lines:

1407 Edelbrock 750 CFM Carb, manual choke, dyno time only, light oxidation
Cost $289.00 new, want $150.00 OBO
For Pictures go to: http://wildaboutcarsonline.com/cgi-bin/clubforums.cgi?forumid=9990286665833&postid=997036 6133430&action=messages&threadid=9970366133430&
Steve Minore
casamperformance@sbcglobal.net
203-623-3135

KQQLCAT

Yes I did switch out the tranny. I don't think that I have seen a small pattern Holley. I might have to go that way if this does not work. 750 CFM a little big for this engine?
Thanks
Pat

KQQLCAT

I finally fixed my bogging Rochestor 4GC. All it took was taking off and replacing it with an Carter AFB off from 1963 Vette. I can't believe how much better it runs and I can still use the stock air cleaner. Thought I would post this just in case anyone else has the problem I had.

Pat

jrzybob442

You may not know this but a 4GC has an air valve just like a Quadrajet. What usually happens is that the spring loosens over time and need to be reset. It's funny, because I was just posting this to the Tech Pages at WAC today.

It will show up here later today: http://wildaboutcarsonline.com/cgi-b...=9990357147919

It is up

Nimrodinder

Thats the kind of solution I like ... I've been looking into Holleys and Edelbrocks but wanted to keep my stock aircleaner so hadn't got far with it. I wondered if the Carter AFB would work. Will only the 63 Corvette one work or was this common on many engines then? I've still got the crappy slim jim trans, so would it work with the TV linkages? I am looking to swap to 700r4 using the adapter you've used but Tony says they wont sell the adapter kit only anymore. Only complete transmissions all done.