andy's88

I'm having a problem with the carb the engine hesitates when I try to accelerate I have to feather the pedal to make it work. I installed new kit in it, still does not work I think it's the accelerator pump. Any ideas?

oldcutlass

It could be the accelerator pump. It could also be a timing issue.

Tedd Thompson

Which carburetor is on your car ,there were two types I believe? If you can take the air cleaner off and see the accelerator nozzles check and see if you are getting a good squirt of fuel, if not that is probably it. I have had lots of problems with the new accelerator pump cups going bad in a very short time... Tedd

andy's88

I'll check the timing, the carb is a side draft used in 49 and 50 Thanks

redoldsman

Teddy:

If this is the original carb, he can't do that because the 49 and 50 carbs had the airhorn on the rear of the carb. I am guessing the pump which is probably a victim of ethanol.

Tedd Thompson

I couldn't remember when they switch to the 2gc. I have seen 50's Olds with the 2gc but who knows what is original after 60 some years..... Tedd

redoldsman

I imagine over the years a lot of those have been replaced. I actually have an air cleaner for one. It needs some work but I think it could be fixed. Those 49 - 50 carbs were pretty goofy.

Tedd Thompson

Ya, I had a aluminum two two setup for a 303 once upon a time with those carburetors. I think it went into the aluminum scrap pile about 25 years ago... Sad.... Tedd

D. Yaros

It also could be a distributor vacuum advance problem. At least such is not uncommon in mid-fifties GM cars.

Ozzie

It sounds like an accelerator pump problem, but check the timing just to be sure. If it's a Rochester, it should be an "AA" model. The number for 1949 was 7001570; 1950 was 7002570. Since you did a rebuild, I'm assuming that you made all the adjustments successfully. The carburetor book says that for 1949 use the outside hole in the pump lever; for 1950 use the center hole. I'm not as familiar with the AA as the 2GC/4GC, but if the pump works similarly in a well, and if it fills with a ball check at the bottom of the well, be sure that the ball check seals completely. This is crucial for good pumping action. If it leaks at all you'll have to carefully resurface it as you would an engine valve seat. Also, the "lip" of the piston should contact the wall of the well completely. Some pistons also have a "check" or "bleed" in the center of the piston. Do a close examination if it is so equipped. New doesn't always mean "good".

andy's88

Thanks for all help timing is good I'm going to pull it apart and check it out carefully I also think the Ethanol is the problem I've had the car for 20 years the problem started a couple years ago. Where good place to buy rebuild kit?

redoldsman

I bought a kit from Fusick for the 4GC on my 54 and it had an ethanol proof accelerator pump. It stated so on the packaging and I believe the plunger was blue. Most new kits probably do have the ethanol proof plunger. If it has been on the shelf for a number of years, probably not. By the way, if you ever need an original air cleaner for that car I have one. It needs a little work but it is not rusty.

Ozzie

Fusick does show the kit as being available.

https://www.fusickautomotiveproducts...ileCatalog.pdf

Their number is 1116. It's a bit pricey @ $83 + ship, but these kits are difficult to find.

There's also one on eBay, but not much price advantage.

https://www.ebay.com/itm/ROCHESTER-A...!US!-1&vxp=mtr

Daytona Parts Company shows the same.

https://daytonaparts.com/find-your-carburetor-kit.html

andy's88

Installed a rebuilt kit still hesitates I'm done need to change carb. I tried to it keep stock but no fun to drive like this. What would be good carb. to use and linkage? Thanks

Ozzie

I realize that you are discouraged, but let me assure you that it is performing that way because something is not correct. I have an old friend that once owned a 1949 88 with Hydramatic and the AA carburetor. While he had modified the valves and exhaust some, the intake remained stock. He's always told me stories about how he would race motorcycles of the day and win. Hence he didn't have the "bog". The AA carburetor was used in 1949 & 1950. In 1951 they changed to a model BB carburetor which was a two barrel downdraft. The intake manifold also changed in 1951, so I don't know if you could just change the carburetor. If you'd like to put a bit more life in the old girl, you might try to change the manifold and everything above it to one of the 4 bbl. jobs they came with in 1952 or 1953. These were also 303 engines. In those days they also used Carter as well as the Rochester carburetors, hence, you might find either. The 4GC in 1952 was 7004300 (auto.) or 7004800 (manual trans.). In 1953 it was 7005600 (auto.), 7005700 (manual), or 7006250 (Dynaflow). A complete donor vehicle would be great. Get everything from the manifold to the air cleaner & linkage. Then refurbish everything.

kirkwoodken

If you have any Rochester GC series carb, be aware that the enrichment jets are hidden behind two lead plugs. On almost every one I've worked on, the enrichment jets are plugged and CANNOT be blown open with 150# air pressure. You must carefully remove the lead plugs to clean the jets. A piece of "tag" wire usually works. Small lead fishing weights can be used to re-plug the access holes. After a thorough cleaning of the outside, I usually put a little dab of epoxy over the lead ***** after making sure they don't leak.

The enrichment jets are located at the lowest part of the carb, so dirt tends to collect there. Also, NOT ALL ENRICHMENT VALVES ARE THE SAME. If everything looks alright, accelerator pump working, timing right, floats set correctly, etc., and you are still getting a bog, the enrichment valve is probably not passing enough gas for power/acceleration. With the valve stem flush with the cross slots in the valve, you should be able to blow a good amount of air through the valve. Sometimes the stems are not long enough and sometimes the gas holes on the sides of the valve are too small. The valves can be taken apart and larger holes can be drilled. A few thousandths is usually enough.

If you make sure the enrichment circuit is functioning properly, you will be surprised how well the Rochester GC's work. But, don't take it for granted that YOURS will work correctly. Check that all the holes are open and valves are working as designed.

andy's88

Not sure what a GC series is, mine is a type AA
Thanks.

Ozzie

The GC series is a long running series of Rochester carburetors (2GC & 4GC) which followed the AA models (1949 & 1950) & BB models (1951). They were downdraft carburetors which were used on the Oldsmobile stage 1 V-8 engines through 1964 and stage 2 also beyond 1964.

Oldslincs

I have a 1950 Olds and it was hesitating badly just as yours is, even after installing a rebuild kit. The kit didn't come with a replacement Power Valve actuator (aka the Power Valve Diaphragm unit), so I'm assuming yours didn't either. Mine had a note stating that old actuators could be sent to Daytona Parts Co. for reconditioning (btw, the kit didn't come from there originally; the note just referred to the latter company as a source of reconditioned actuator units).

I eventually found that the old Power Actuator was the cause of the hesitation problem, so replacing everything else present in the rebuild kit didn't fix the problem. I'm sure you know what I'm referring to, but just to be sure we're talking about the same thing - the Power valve actuator is the spring-loaded spindle device with a flat button or hexagon nut at one end and a rubber diaphragm and triangular aluminium housing at the other. It's held in place with three countersunk machine screws through the housing.

If its never been replaced, it will likely have a flat button at the end and the spindle will be a snug fit inside the bore of the housing. If yours is like this and the accelerator hesitates, as you describe, the problem will likely either be a hardened rubber diaphragm not allowing smooth actuation and/or the spindle is not moving smoothly and freely inside the bore of the housing. If the rubber diaphragm looks OK, check the spindle and clean it (not easy with spring and housing in the way) to get it to slide smoothly.

If it's been replaced with a repair-kit unit, at some point, the spindle will probably be a fairly loose fit inside the bore of the housing and instead of a flat button, it will have a hexagon nut that tightens flush to the end of the spindle. Because of the loose fit of the spindle, over time it 'chatters' inside the bore of the housing creating circular grooves on the shaft which prevents smooth sliding movement to actuate the power valve when you 'put your foot down'.

This was the case with my AA Carburetor. I've attached the instructions that came with the replacement spindle and attached diaphragm that I was very lucky to find in the trunk, given to me by the previous owner. After fitting the replacement unit - no more hesitation and the acceleration is nice and smooth. I was searching for info about where to buy another replacement because over time, the one I've fitted will no doubt groove up and start sticking again, which is why I stumbled across your post, so I felt I had to share how I fixed the same problem. Hope this helps.

D. Yaros

Quite often hesitation problems in these 50's era rides is caused by a vacuum problem, such as the distributor vacuum advance.