Tedd Thompson

After another failure of my 55's accelerator pump I think I have finally found why the cups are failing.It appears that for some reason the accelerator pumps that have been coming it the kits and the ones I've bought on line are about 1/8 inch to long and causing the cups to bottom out and roll up on the side of the barrel causing the piston to cut the cup.I found this out by accident when I ordered three accelerator pumps from three different places, all for 55 4GC carbs, all were different lengths, one wasn't even for a 4GC carb I don't think. So if you are having this problem check to see if your piston is bottoming out. If and when I figure out which pump is correct I'll post the number and place where I got it. At this point I'm pretty sure this is the problem and why some are having the same problem and others are not...... Tedd

47 Convertible

Sounds like good detective work on your part Tedd.

Seems like lots of parts on the Internet including Ebay are mislabeled as "fits (make/model/year of your car)". Of course the site then puts in the caveat "this isn't our data and seller is responsible for accuracy." I've lost track of the number of parts labeled "fits 47 Oldsmobile" that aren't even close to fitting 46-48 Oldsmobiles. Sounds like you're having the same experience with your 55.
Jerry

Quadrajet Power

Tedd, I am in the process of creating a 4 Jet parts and kits section to my store and ebay store. These parts are getting harder and harder to find, and more expensive. I will only stock best I can find items. There are 5 different lengths of pump assemblies ranging from 2.924" to 3.327" and two different diameters (3/4" and 21/32") that were used. I typically sell complete assemblies, and not just replacement cups. If you have tracked down a good working item, and would share the part number with me, I would add them to my store offering.

Tedd Thompson

Thanks for the interest and yes I will as soon as I find the correct pump length. Do you know from what points one would measure to get the lengths listed? The 3/4 inch cup/barrel diameter appears to be the correct size for my particular 4GC but all the pump shafts I have now appear to be to long.At a guess I would think the shortest assembly(2.924) would be the size I need but I don't have one of those to check.... Tedd

Charlie Jones

Tedd ,
The factory part number for a 55 Olds four barrel accelerator pump is 7000208 .
If this helps.

redoldsman

Tedd:

I used the kit from Fusick when I rebuilt my carb and have had no problem with it and it has been in the car for about 2 years. I have no idea of the length of the pump.

Quadrajet Power

Of course, my books don't show that number. I'm still researching.

Charlie Jones

That part number was from my 1963 book .
I looked the acc. pump up in a 1972 edition of the Olds parts book , and it listed the pump for 54 thru 56 4 bbl. as part 7026826.

Tedd Thompson

Thanks Charlie, those numbers may help. One of the issues I'm running into is some of the distributors have there own number system that don't match up to factory numbers. #07390 77776 This is a NAPA number for a accelerator pump that is too long and according to the young counter guy that is the only pump listed through Napa.Two others ordered on line are different lengths, one is still to long the other looks like it is a Edelbrock style and I have no idea what it fits.

The search goes on but I think I'm on the right track.Gotta get it figured out, show season is almost here and my car is apart on all ends. Back with more when I get it.... Tedd

Charlie Jones

Tedd,
Google is your friend :
http://www.ebay.com/itm/Dealership-N...-/222271055582

Tedd Thompson

But those are the black cups that aren't supposed to be alcohol resistant. I think they replaced the leather cups and were before the first light blue one that also weren't very resistant.I could be wrong on this though, to many changes and to many sizes. Thanks for the tip on Google though I sometimes forget the easy ways.... Tedd

Quadrajet Power

I did find a cross reference to the 7026826.
It is a 21/32" base, but I do not know the length. I will measure when they come in.

We have those assemblies ordered with blue alcohol resistant pump cups. We have been ordering in phases for all the 4 Jet and AFB parts to add to our Quadrajet parts. These have not come in yet, but expecting them next week.
If you can wait a week or so, we can supply it for you.

Charlie Jones

Tedd,
If memory serves me correctly , the pump plunger can be changed separately .
You might consider buying these anyway and putting a new "blue" plunger on at least one of them .
At least this way , you will be sure it is the right length . And has the right spring etc .

Tedd Thompson

Charlie good idea. I have a couple of pumps coming in next week. I need to check them out first.

Quadrajet that is interesting that it shows that the cup is 21/32 . The 3/4 cups seem to fit correctly in the barrel but what do I know I don't have a 21/32 to compare it to...... Tedd

Charlie Jones

Tedd ,
Another thought .
Are you absolutely sure that you have a 1955 Olds carb on your car ?
Do you have the three cornered tag on one of the airhorn screws ? If so , please post the number on it .
Does it show any sign of a "rebuider's" tag ? Some of these "rebuilders" were notorious for mixing parts and "making it work ".

Tedd Thompson

I have known the car from 1978 and It was stored for about 10 years before that so what happened before that I don't know. I know I haven't changed the carb and the carb tag is still on the carburetor. I believe it has been totally rebuilt twice and at least three accelerator pumps installed. My car is at my buddy's shop so I can't run out and get the number but maybe tomorrow if I go to town (50 mile round trip)... Thanks ...Tedd

Tedd Thompson

Well my car is running as good as it has in a long time but the fix isn't a Eureka a moment. Actually my friend (Steve Larson) and I decided to combine two pumps to get the length diamiter and thickness of the cup plus the length we were looking for.

We used a cup out of a Walker 64318 pump and the original pump shaft that was in the car. The Walker cup was thicker in the area that comes apart and was 21/64 in diamiter. I'll know more after a few hundred miles. This problem could all be because of using a 3/4 cup in a 21/64 barrel all a long.

If this fix pukes and fails I'll let you know. I wish it was as simple as putting a certain part in and forgetting it and for all reasons it should..... Tedd

Ozzie

If the carburetor is number 7000700, my books are also showing 7000208 as the part number for the pump plunger assembly (plunger, rod, & spring). Supposedly it was used in the 1954-56 Olds 4 barrel Rochester carburetor. It was also used in the 4 barrel Rochester on the 1959-61 Chevrolet 283 with carburetor numbers 7019004, 7013010, 7015010, & 7019004. The 7000700 has a tapered pump well. The cup will fit tighter at the bottom. You should be able to determine the needed cup diameter by measuring the diameter of the lower 2/3 portion of the well. There are two ball checks involved. One is at the bottom of the well. The other is in the pump assembly. Leaks at either will diminish pump effectiveness, as will a damaged or ill fitting cup. The ball check in the pump assembly was included to vent percolation in the well. In the "old days" some "hot rodders" would solder closed the ball check in the pump and force it to fill exclusively through the bottom of the well, supposedly making it pump better, as they felt that they didn't have the percolation problem and preferred the better pumping. There is no good substitute for having the correct pump plunger assembly. There is a dimension that should be checked that affects pump plunger travel. With the throttle valves FULLY closed (idle-speed and fast idle screws backed out completely) the dimension from the top of the air horn to the bottom edge of the pump plunger shaft should be 1-1/16". You can bend the pump rod (link) to correct. Be sure that the bottom pump spring is correct as it limits the downward motion of the pump assembly. Over travel "might" damage the cup. If you've already covered all of this, please forgive. I'm just a old guy trying to cover all the bases.

Quadrajet Power

Good to know. So it was the smaller pump cup. They will expand a bit when in fuel.

Tedd Thompson

Thanks Ozzie, some of this I have covered in my oddessy with this problem. I did not have the dimension from the top of the air horn to the bottom edge of the plunger and that would have been a help and maybe solved the problem a lot sooner, perhaps I could have done away with mismatch parts also.That usually means you have messed up some where along the way. I''m working with a friend mechanic who works of older cars a lot and rebuilds about 12 carbs a month (he rebuilt my original carb 12 years ago) he has been stymied right along with me. We don't feel comfortable that we started out with the correct pump and cup from the start and the three accelerator pumps we bought are all different to compound the issue.I was hoping this would help others because this problem has been getting worse as time goes on but I feel though my car might be fixed I don't feel comfortable this is a good fix for everyone.... Tedd

Tedd Thompson

Thought I would update this So far so good with the mismatched parts. Probably only 300 or 400 miles on the clock sense the rebuild and it's a pleasure to drive. I'm thinking about a going somewhere distant probably car show related but haven't figured where as yet..... Tedd

47 Convertible

__________________________________________________ __________

Tedd, if you are still planning on moving to the Boise area drive on up to Emmett for the July 15th car show in their Park. That would make a good long road trip to a great car show (my favorite). It would be an opportunity to meet lots of car guys from the region. Emmett is about 30 miles NW of Boise. No charge to show the car but get an entry form off the Internet from the Emmett Lions Car Show site.

I'm planning on driving my 47 convertible there from SW Washington State. I drove my 36 Chevy two years in a row. Your 55 Convertible would be a real standout. Best to be there at or before 7 a.m. on show day to get a decent spot to park.
Jerry

Tedd Thompson

I know Emmett well. I have been looking for property in the Garden Valley area not to far away. The only bad thing about going to Boise this time of the year is that stretch between Reno and the Idaho border It is HOT with out AC. I was thinking more about hitting the Oregon coast, somewhat cooler...... Tedd

54oldsmobile88RW

Are you saying I'm going to have fun with my 54 Rochester? Oh boy! 🤔

Tedd Thompson

Does it stutter/bog on acceleration from low RPM? If not you are good to go. If it ain't broke don't mess with it... Just messing with you.It's not that difficult of a carburetor to rebuild if you can get the correct parts to begin with.

So far I have had no problem with what I have done but Redoldsman used a kit from Fusick and had no problems and by now hopefully Quadrajet Power should have the correct pump parts if that's all you need..... Tedd

54oldsmobile88RW

secondary is rusted solid. No visible damage that can't be cleaned hopefully. Taking it to the same guy that did my 79 quadrajet and my autolite 4100. Haven't had any issues with his work. Although, i will probably get the fusik kit in addition to the eBay one i have now just to be safe. Thanks.

btw.... right now my engine only oozes weird colors and is scattered across the garage... lol

Tedd Thompson

I thought they all did that! You will see a dry bottom baby before you will spot a dry bottom first generation Oldsmobile.... Hang tough and keep wrenching after all you might have fell in love with a ugly car instead of that cool 54.... Tedd

Super88chris

No wonder I’ve been having this same issue, I ordered my rebuild kit on rock auto and it came with a blue plunger base. I used it a few months til I decided to open up my carb and what do you know, the rubber base was already cracked! And that’s just from starting my car in the yard with no actual driving! Anyways I put the old one back in that I got the car with which has a black base and was not cracked and it seems to be better. But I agree and I’d like to get the correct one as well. Did someone specify which of those part numbers was correct for the 55 olds 4 bbl?

Tedd Thompson

What I've been told, the black cups were made before the addition of alcohol added to gas and don't last very long with today's gas. I even went to an old time leather cup once, and it worked for a while till I let the Old girl sat through a winter and that cup dried out. I have no idea how old that kit was though when I bought it, most likely somewhere in the twenty, thirty-year-old range. Buy the way just to confuse things, there are two blue colored cups, one lighter than the other. Supposedly, the dark blue is the better of the better of the two, but I have nothing but hear say to back that up. My car has been good for about 7 years now with the set-up I have now, many marathon trips under her belt, ready for another, your luck may vary though....Tedd

Super88chris

right on thanks tedd. Not sure if I will be able to piece them together so I guess I’ll just buy the dark blue or even the leather one most likely. I know with my kit from rock auto the check ball that sits down in the well makes it so the bottom spring doesn’t sit flat down there, is that ok? I decided last week to put in the ball and see what it does and it actually seems better! Before that I had to push on the gas about a quarter of the way down before it would start squirting any fuel

Supernice88

Make sure you have the height adjustment made correctly shown in the manual. When you look down into the carb you should see the gas squirt immediately as soon as the throttle moves.

66-3X2 442

I use pumps provided by Daytona Parts. The cup is red and the pump comes already assembled and the cup has the garter spring also. I use them in all of my tri carb builds and have had great results.
https://daytonaparts.com/

Super88chris

I don’t know the exact height because I don’t have the manual. If you have a picture from the manual that shows the height that would be great. Mines pretty close to squirting right away but not exactly yet I don’t think

Charlie Jones

You can get them here:
Pre-owned copies are best.

1955 oldsmobile shop manual in Parts & Accessories for sale | eBay

Super88chris

ok thanks I’ll check there

Supernice88

Here is a thread discussing this issue. https://classicoldsmobile.com/forums...stment-165631/

Super88chris

I’m not sure if I was on this thread, but I think I was telling how ever since I set my timing, my car will run normal at idle the sometimes just drop like it’s barely staying alive. I thought it was the points were slipping or opening too much but I don’t think so. As I was tuning my carb I’d get the idle at 800 rev a few times then it would drop a great deal or sometimes it would just do this on its own. It’s on my 55 olds super 88. Is there a way to make sure the base in the distributor is tighten down? Also on the lobes in the center, if some are worn more than others, should I set my points gap to a worn lobe or a higher one?

Super88chris

also I’m hearing like a zap sound while I’m turning the engine over like something arcing

Vintage Chief

If you can visualize some lobes are much higher (not worn) than other lobes (much lower), you need a new distributor most likely. Arcing can be caused by several issues. The purpose of the distributor condenser is to absorb spikes of unwarranted/wandering energy and prevent arcing between the points each time they open; therefore, you may need a new distributor condenser. I think you need to read up on what causes the magnetic field to collapse inside the ignition coil and the difference between the primary windings & the secondary windings of the ignition coil as they relate to the collapse of the magnetic field. Google should work well for this. In the following demonstration, the narrator refers to a "knife switch". Think of the knife switch as your points (opening & closing). Note what happens as the points open - the field collapses. Also note when she describes the role of the capacitor. The capacitor is your distributor condenser.

Arcing can also be caused by a bad metal button on the top of the distributor from which voltage is supplied from the ignition coil to the distributor cap. Bad distributor cap, cracked? It could be arcing of the rotor as it rotates, examine if for carbon build up, wearing, abrasion &/or cracks.

Super88chris

Yes the video explains a lot but I’m not sure if that’s my issue on this. The drop in RPMs is my bigger concern