Vintage Oldsmobiles Curved Dash, Limited Touring, Models 40, 53, 66; Series 60, 70, 90

New findings on the 4CG accelerator pump problem

Old March 24th, 2017, 09:56 AM
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New findings on the 4CG accelerator pump problem

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
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Old March 24th, 2017, 10:33 AM
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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.
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Old March 24th, 2017, 01:25 PM
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Originally Posted by Tedd Thompson View Post
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

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.
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Old March 24th, 2017, 04:06 PM
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Originally Posted by Quadrajet Power View Post
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.
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
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Old March 24th, 2017, 10:09 PM
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Tedd ,
The factory part number for a 55 Olds four barrel accelerator pump is 7000208 .
If this helps.
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Old March 25th, 2017, 08:45 AM
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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.
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Old March 25th, 2017, 03:19 PM
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Originally Posted by Charlie Jones View Post
Tedd ,
The factory part number for a 55 Olds four barrel accelerator pump is 7000208 .
If this helps.
Of course, my books don't show that number. I'm still researching.
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Old March 25th, 2017, 06:19 PM
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Originally Posted by Quadrajet Power View Post
Of course, my books don't show that number. I'm still researching.
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.
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Old March 26th, 2017, 07:37 AM
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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
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Old March 26th, 2017, 08:09 AM
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Old March 26th, 2017, 09:05 AM
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Originally Posted by Charlie Jones View Post
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
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Old March 26th, 2017, 01:18 PM
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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.
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Old March 26th, 2017, 01:19 PM
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Originally Posted by Tedd Thompson View Post
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
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 .
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Old March 26th, 2017, 01:58 PM
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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
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Old March 26th, 2017, 04:51 PM
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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 ".
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Old March 26th, 2017, 08:15 PM
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Originally Posted by Charlie Jones View Post
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 ".
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
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Old March 28th, 2017, 11:51 AM
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A little more info don't know if this will help

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
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Old March 29th, 2017, 12:45 AM
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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.
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Old March 29th, 2017, 06:25 AM
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Originally Posted by Tedd Thompson View Post
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
Good to know. So it was the smaller pump cup. They will expand a bit when in fuel.
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Old March 29th, 2017, 06:48 AM
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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
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Old June 19th, 2017, 08:42 AM
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Up date

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
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Old June 19th, 2017, 11:55 AM
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Emmett ID. Car show

Originally Posted by Tedd Thompson View Post
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
__________________________________________________ __________

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.
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Old June 19th, 2017, 01:08 PM
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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
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Old August 6th, 2017, 05:08 PM
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Are you saying I'm going to have fun with my 54 Rochester? Oh boy! 🤔
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Old August 7th, 2017, 07:07 AM
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Originally Posted by 54oldsmobile88RW View Post
Are you saying I'm going to have fun with my 54 Rochester? Oh boy! 🤔
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
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Old August 7th, 2017, 03:08 PM
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Originally Posted by Tedd Thompson View Post
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
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
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Old August 7th, 2017, 08:18 PM
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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
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