cmpcpro

Hey guys can anyone offer any advice on tuning my new carb? I've spent the last week or so freshening up on tuning a carb as it's been years since I've touched one.. I have the 4gc. I know a lot of people say to start the idle mixture at 2.5 turns and go in from there but when I fire the motor I have 19 on the vac gauge and turning out the pass side needle to about 3.75 turns makes it run the fastest and bring the needle closer to 20 or so but then the drivers side needle doesn't seem to do much. On top of that I've got a bog or stutter from idle to giving it just a bit of gas and then it instantly clears until you do it again.. also noticed when idling I can close the choke valve with my finger to more than 3/4 and it doesn't do a thing.. I would think that would change the idle but maybe not.. any ideas would b greatly appreciated! I really want to drive my car again lol!!

cmpcpro

I think I found the issue, the accelerator pump looks like it's barely squirting anything out on pass side and even less on drivers side! What a great restored carburetor!!

Quadrajet Power

Sounded like accelerator pump on the hesitation issue. Your idle is a different thing though.
Adjust the idle screws one at a time until you get highest idle or vacuum and you should be good.

cmpcpro

Thanks I got the idle screws right but now I don't know what to do about the accel pump.. I get fuel just dribbling out of it, nowhere near a strong stream like my old one. Could there be an easy fix for that? Thanks!

Tedd Thompson

It may not be your re builders fault For some reason the accelerator pump cups on 4gc carburetor kits are failing in a alarming short time. I'm on my third set and a'm getting ready for my forth now. On my car the accelerator barrel is as smooth as a baby's bottom yet I have had two that were rolled up and were laying at the bottom of the bowl.They just came apart, one in less than a week like the gas just ate them up.I know that the last two were labeled as alcohol fuel resistant and were dark blue in color but didn't act as though they were (Ebay kit) . The first one lasted almost 12 years and I have no complaints on that one , wish I knew what kit that one was. I'm now going to try a Napa accelerator cup #2-407 and see what that does, it's getting frustrating to say the least.... Tedd

cmpcpro

Thanks for the info but mine is new with two miles on it so it seems to be a failure off the bat. There is a guy who rebuilds these carbs with NOS kits but I stayed away because of the ethanol deal.. I don't know anything about these carbs really, does this carb have to come off and apart to take care of this accel pump now? Thanks for the help!

Quadrajet Power

I would recommend a good complete pump assembly with ethanol compatible cup with garter spring. The leather type require soaking before assembly and just don't work as well these days.
I do still build the 4GC's, but don't keep parts in stock for them.

You would have to pull the top off of the carb to change the pump, and I would prefer to do it from the bench myself, but not required.

cmpcpro

Thank you! Do you know where I can get one of these? I can just unscrew the top and drop it in? Could anything else in this carb be causing the acc pump to do this? It's a 7007221

Tedd Thompson

You could just pull the top off the carb and address the accelerator pump if you can hang over the car without problems. It's a lot easier if it's on the bench though. If you could ask your guy with the NOS if the cups are leather or synthetic. Leather works best if it isn't dried out and deteriorated with age. Let us know what you find out.... Tedd

cmpcpro

Thanks Ted, will a whole new accelerator pump assembly surely solve this? I'm wondering how they managed to botch this one.. I noticed it looked a little damp around the boot like maybe fuel was going over it

cmpcpro

Also, I'm wondering if something else is happening in this carb other than the acceleration pump because when you give it gas to say about 2500 or so it still runs rough a bit now.. keep in mind when I first installed the carb the dist had a brand new mos vac advance and was a little loose so I believe the new hard line I installed advanced it as driving with the new carb it drove fine but was pinging. However after the first Drive of running Good it was untouched and parked for thirty min and then started running rough ever sense. I've since retarded the dist but it still runs rough.

m371961

I would also check that pump nozzles are clear. I had a problem with this a few weeks after rebuild. Don't know how it got dirt in nozzle, but it did.
Google Rochester 4G, there are drawings and looking at them you can see how the ball check, acc. pump and nozzles all work together. IIRC, the is also adjustment to check if you are getting correct stroke of pump.

Tedd Thompson

You might give this you tube series a quick look also. If you choose to rebuild your carb, take some pictures of how the linkage goes together. This can be a problem remembering after a few days....

cmpcpro

Thanks guys, I'll check for the pictures. Thanks Ted I actually have already seen those the other day lol but thanks again

cmpcpro

Well guys I went out today and took the lever off the accel pump and really cranked on it a bit and right off the bat if I run it through its range I can feel it like bind or stick for a second pushing it down, when pushing it all the way I do get a stronger stream but not strong enough and weaker on the drivers side and I noticed when pushing down on the pump and the boot flexed that the boot is all cracked and eaten up! I'm wondering if the rest of this carbs rubber parts are being eaten away this quickly! I'm thinking I need to find a good rebuild kit and maybe have this redone..? Thanks again for the help guys!

Ps - I am taking apart my old working carb now, just the top. I'm wondering if I should use that accel pump. It seems to work good and the rubber boot looks new. For all I know this could only be a couple years old.

cmpcpro

Here is a pic of the old carb's accel pump. The spring in the housing doesn't seem to want to come out but I'm thinking about swapping the pump spring (should I just try to pull harder?) and boot to the new one if you guys think it's worth a try.

cmpcpro

Took apart the new one too and the accel pump was junk and the plastic part was so loose on the shaft that with the spring on it it was bending it and making it bind. The cup was a blue rubber with a spring in it.. almost identical in size as mine in the old one but mine just had a black rubber cup. I put my old one in the new carb and now have a great strong stream like the old one. For the hell of it I fit the new one in the old carb and it wouldn't even go down all the way.. maybe that spring is making the cup too big.. putting it back on the car now but I did notice a diffeeence in the gaskets.. I will show pics of the old and new but the new has more gasket material over the rear bowls..

cmpcpro

Here is the now old accel pump that was in the new carb. Glad to have it out of there!

Tedd Thompson

And to make things more difficult there are three different cup sizes 21/32 #ap1737 43/64 #ap172 and 3/4# ap486. I think the 3/4 size is correct for our carburetors but who knows what has been changed after 60 years. Let us know what works when you are all finished.

That black accelerator cup looks suspect to me. That is the color before they went to the suppose to be alcohol friendly light blue then dark blue more better one (sorry for the double negitive). But if it works go for it. I'm getting more and more ignorant as I learn more more things..... Tedd

cmpcpro

Hey Ted,

I checked mine with the caliper and both were the same, just the cup on the new one had a spring in it and I think maybe that was making it not seat correctly. I'm not sure if the black one is ethanol efficient but I can say the rubber boot on the new one just about deteriorated on contact with fuel, while the boot and accel pump on the old one has been in for at least three or more years and still looks and works great. I'm not sure if the rest of this rebuild is any good but the accelerator pump works so amazingly better I would almost go out on a limb and say I'd much rather have whatever kit the old one came in and replace it every five years than the supposed ethanol resistant crap that was in there and lasted 5 miles. One of the best builders on the Olds club site who everyone loves uses NOS kits and claims he has no problems with ethanol, and I'm beginning to think the reason everyone loves his rebuilds is because those kits were probably much nicer than this new junk! Have you seen anything like that top base gasket and how there is more material on the new one? I wonder if that is even correct.

Tedd Thompson

If you look on a 4GC site that lists and shows all of the Rochester kits for all the different 4GC's that were made ,probably 20 different kits it's a wonder we get any of the correct parts.... Tedd

cmpcpro

Tell me about it! I'm about to go nuts with this thing. Choke is good now, idle mixture seems good but still have a misfire or stutter when giving it gas and when holding throttle open... new plugs and wires I'm starting to wondering if one of them is bad.. also the new or old accel pump doesn't bind like the old one and gives a good stream when you really open it but just giving it very little throttle it barley dribbles a bit.. am I wrong in thinking that even slightly cracking the throttle I should get a good couple streams? Thanks again for the help!

cmpcpro

Oh by the way my vacuum advance wasn't working. I tested the old one tonight with my vacuum gauge and it wouldn't hold vacuum.. so to me it looks like the previous owner advanced the engine to make up for it.. I'm wondering if now that I have a NOS unit on there (I did retard it) that I should be checking on the mechanical advance.. does it have any springs or anything they could have taken off? thanks!

cmpcpro

Hey guys, I really need some help here! I'm lost! I can't get this thing to run right for the life of me! So originally my 56 Olds 98 had a bad vacuum advance. Someone jammed a 10mm vacuum nipple in the threads and when I went to install my new hard line I realized the threads were stripped. Once removed I found it wouldn't hold vacuum at all. I bought a NOS on eBay. Anyway while doing this I replaced the carburetor as the one on there seemed to be acting up a bit, it was set so rich at idle the choke wasn't even working, and the car would overall run pretty nicely but it would have a slight stutter off idle (giving it a little gas from a dig). So I replaced the carb with another 7007221 Rochester 4GC that was rebuilt by a carburetor builder. Once replaced and set up I still noticed a slight bit of a stutter off idle but it now ran rough at idle and pinged with moderate throttle, clearly because of the new advance. To my surprise when checking the timing the mark was about at the top/middle of the motor when at idle, so now it's back to about 5-7btdc. That solved the rough idle and pinging and seemed to take most of the stutter off of idle away. The issue is, it seems once I get it running decent it will change on the next drive. It seems sometimes it will run great on a quick trip with no stuttering off idle, and then the next trip I'll get the stutter/bog at a green light and then once I get over it the car runs fine.

I've checked the timing again tonight and it's still set, as I give it gas it will go back up to the middle/top of the balancer so I think that is fine, but this bog off idle is making it hard to drive. Now one thing I've noticed is the new accel pump in the rebuild was junk and felt notchy. I also noticed that if you just give it just a very slight bit of gas it doesn't do anything until you give it a little more, then you will get a bit of fuel, but the pass side seems to get more, now if you open the throttle a little more you will get two shots from each side, but both carbs seem to have this characteristic. Should I be getting two strong shots or anything when you just barely hit the throttle? I would assume so and that seems to be the spot I'm having my issue at. It just seems weird that both are doing it, yet then again I had the problem with both.
Is there anything else that can cause an intermittent stutter/bog off the line like that? I don't think it's going away completely, I think it's just teetering on the line of being barely noticeable and noticeable/an issue. I have a Pertronix Ignitor 3 in the dist. The issue was there before it. I have new cap, rotor and wires and plugs too. Fuel pump was rebuilt not long ago, it looks new. Fuel tank and sender are new too. New fuel filter also.

Any help would be greatly appreciated! I have had my car up for months now and I just want to enjoy the darn thing!

cmpcpro

Well I think I'm learning this carb here. So here's the deal.. shortening the pump made it worse.. so I started thinking maybe it's normal for that brief second of throttle to not have the spray because its jumping from the idle circuit and I had an issue with puddling before so I know the idle circuit can run rich and affect the off idle performance.. so everyone always says to tune to highest vacuum or RPM but my friend who worked on these new at a Olds dealer said that's wrong on these. He said turn the screw in until the idle dips and back it out a half to 3/4 of a turn.. well that's what I've been doing but tonight on this new information I decided to set the pump back to spec and set the screws to half a turn out from idle drop.. seems to get better, went in another 1/8 of a turn and now it seems to be almost gone.. however that's happened before and it's come back so we shall see but I think I'm on the right track.. also reading all through the Internet I found another guy on a forum who said his old timer friend said the same thing and it fixed his issue too, so I'm staying positive! If I clear it out and then let it idle a second and then back on it right after it's smooth, only after sitting a few seconds does it get the stumble so I really think puddling is the issue here. Fingers crossed!

66-3X2 442

The accelerator pumps seem to be a problem on the 4gc carbs. I am having the same problem with a couple of 64 330 carbs. I found a place that has great pumps and kits for these. I just got a kit and extra pump for my carbs and they look great. They have the spring under the cup for proper sealing. I also bought 9 pumps for 66 3x2 carbs and they also look great. They came highly recommended and I will know later this week if they help. Here's the link.

https://daytonaparts.com

Another thing that might be happening is,some of the kits come with 2 different length springs that hold the check ball in place under the booster. If the spring is too long,it could keep the ball from opening off the seat. Also check to see if the 'T' retaining pin isn't too long holding the check ball from opening. You can also bench test the pump by filling the bowl/pump well with gas or alcohol with the check ball and spring in place to see if it's pulling from the bowl after the pump shot.

cmpcpro

Thanks for the info!

Bseward78

Hey guys
I had ordered a HYGRADE kit on Rock auto for my 4GC Rochester carb which did not last longer then a week.... Had same issue with the accelerator pump in that kit that everyone else ran into. I just ordered a kit from Daytona parts which I must say they were great to talk to and they told me they make all there own parts for there kits. I will let you know how I make out. I must also say that this thread was a huge help in getting on the right track with my carburetor rebuild.

cmpcpro

I'm glad my thread was a help! I ended up using the accelerator pump out of my old carburetor and that solved the problem for me as you can tell the new ones are junk. I also bought a new kit from Walker Products which I haven't used yet as I'm having Ross build me a new motor which includes a new 4GC carburetor. Let us know how the new Daytona kit works though because if it holds up I'll stock up on a couple!

Bseward78

Got the Daytona carb kit today and installed. The parts in the kit are ALOT better quality and the car is running great! I highly recommend them.....