Fuel supply problem

5

'51 Special

Active Member
The backstory is that, after I bought my '51 special at auction in 1992, I soon discovered that it would regularly starve for fuel, acting like it was out of gas no matter how full the tank. I tried lots of things: rebuilt the carb and fuel pump, had the gas tank steamed out, then etched and sealed with Bill Hirsch's products. Nothing seemed to cure the problem. I ended up puting a 2.5 gal. tank in the engine compartment, gravity feed direct to the carb. Not a practical solution except for yard driving, so she mostly sat for almost 20 years. Fast forward to last fall. I was going to do a general teardown, and hooked up a marine tank to the flexible end of the gas line about 24 inches back of the fuel pump. The fuel pump and carb worked like a charm, at least for the ten minutes or so I ran it.
During teardown, I pulled the tank, found it still was holding a gallon or so of 20-year old gas. I blew out the main fuel line and pulled the gas tank sender unit to verify the float hadn't fallen off (it has a cork float held on with copper wire that is soldered to the original float arm, a fix necessary as the original float was holed), and discovered that the fuel line running through the sender unit was completely blocked. Thinking aha, I have cured the original problem, I cleaned the line out by chucking into a drill a couple of strands of wire from a small diameter steel cable. Installed everything, put five gallons of gas in the tank, and tried to get it to fuel the engine. No go. I disconnected the fuel line where it exits the frame to the flex line by the engine, and blew a little air into the tank. Well, it ran gas out of the line just fine. Matter of fact, it siphoned gas out of the tank, and ran about a gallon into the drain pan before I could get the gas line reconnected. While preparing to pour the gas from the drain pan back into the tank, I noticed a few crumbles of rust, so I used a funnel with a screen, thinking: "I hope that rust was in the pa before the gas was.
So, I start the car with primer, and soon it is running on its own. I run it about 10 minutes, shut it off, do other stuff for an hour, and it starts right up again. I drive it about 20 feet, and it starts starving for fuel... just like 1992.
What the hell?? I thought, I'll take off the fuel pump bowl and find it full of rust crumbles, just like I found in my drain pan. So I took off the fuel pump bowl and found not a speck of rust. And, it was full of gas.
I know I could by a new gas tank and sender. (Just $325 plus shipping and I'm made out of money.) But what good would that do? The tank doesn't leak, the sender and all other gas lines flow fuel. The fuel pump gushes gas (at least when I'm looking), the engine runs like a watch when it isn't starved for gas.
I'm about out of ideas, except for maybe again rebuilding the fuel pump.
Has anyone ever had this problem? Did I maybe mis-assemble something 20 years ago when I last rebuilt the fuel pump? But is it even possible to put it back togather wrong and have it still work part of the time? Or does anyone have any suggestions for what to try next?
'51 Special
 
You didn't mention any of these specifically, so if you already checked them, please ignore this.

1. If I am reading your post correctly, the engine will idle indefinitely, but starves when you open the throttle so it needs more fuel. How about a badly worn pump lobe on the cam?

2. A clogged tank vent, so a vacuum builds up in the tank. Running without the cap would be an easy test.

3. A hole in the fuel line that sucks air when the line is under vacuum. You could try a piece of hose all the way from the tank to the pump.


Ray
 
No mention of the fuel filter

'51 Special said:
The backstory is that, after I bought my '51 special at auction in 1992, I soon discovered that it would regularly starve for fuel, acting like it was out of gas no matter how full the tank. I tried lots of things: rebuilt the carb and fuel pump, had the gas tank steamed out, then etched and sealed with Bill Hirsch's products. Nothing seemed to cure the problem. I ended up puting a 2.5 gal. tank in the engine compartment, gravity feed direct to the carb. Not a practical solution except for yard driving, so she mostly sat for almost 20 years. Fast forward to last fall. I was going to do a general teardown, and hooked up a marine tank to the flexible end of the gas line about 24 inches back of the fuel pump. The fuel pump and carb worked like a charm, at least for the ten minutes or so I ran it.
During teardown, I pulled the tank, found it still was holding a gallon or so of 20-year old gas. I blew out the main fuel line and pulled the gas tank sender unit to verify the float hadn't fallen off (it has a cork float held on with copper wire that is soldered to the original float arm, a fix necessary as the original float was holed), and discovered that the fuel line running through the sender unit was completely blocked. Thinking aha, I have cured the original problem, I cleaned the line out by chucking into a drill a couple of strands of wire from a small diameter steel cable. Installed everything, put five gallons of gas in the tank, and tried to get it to fuel the engine. No go. I disconnected the fuel line where it exits the frame to the flex line by the engine, and blew a little air into the tank. Well, it ran gas out of the line just fine. Matter of fact, it siphoned gas out of the tank, and ran about a gallon into the drain pan before I could get the gas line reconnected. While preparing to pour the gas from the drain pan back into the tank, I noticed a few crumbles of rust, so I used a funnel with a screen, thinking: "I hope that rust was in the pa before the gas was.
So, I start the car with primer, and soon it is running on its own. I run it about 10 minutes, shut it off, do other stuff for an hour, and it starts right up again. I drive it about 20 feet, and it starts starving for fuel... just like 1992.
What the hell?? I thought, I'll take off the fuel pump bowl and find it full of rust crumbles, just like I found in my drain pan. So I took off the fuel pump bowl and found not a speck of rust. And, it was full of gas.
I know I could by a new gas tank and sender. (Just $325 plus shipping and I'm made out of money.) But what good would that do? The tank doesn't leak, the sender and all other gas lines flow fuel. The fuel pump gushes gas (at least when I'm looking), the engine runs like a watch when it isn't starved for gas.
I'm about out of ideas, except for maybe again rebuilding the fuel pump.
Has anyone ever had this problem? Did I maybe mis-assemble something 20 years ago when I last rebuilt the fuel pump? But is it even possible to put it back togather wrong and have it still work part of the time? Or does anyone have any suggestions for what to try next?
'51 Special
Click to expand...


In reading your post, I didn't see any mention of the fuel filter. Water that has condensed in the gas tank can get pumped to the carb where it will get trapped in the fuel filter. I had this happen to me once in a 1971 Ford Station Wagon. It ruined an entire weekend vacation trip. The water would get trapped in the fuel filter and block the gasoline. As long as the car was idling or being driven slowly - it would run. But, as soon as you hit the accelerator pedal to take off - it would DIE. When I got home - I siphoned all the gas out of the tank and I found about two gallons of water. I put in fresh gas and a couple of cans of Heet and never had anymore problems. Empty the fuel filter into a clear jar and see if the water and gasoline separate. They will separate noticeably after a little while - it will be quite evident. Hope that helps you out.
 
Ray and BluesBrothersBuicks-
Thanks for the suggestions. Looks like I could have been more clear.
1) I am satisfied that all of the gas lines (there are 4 pieces: 1. in-tank thru the sender unit; 2. from tank outlet along the frame to the flex-pipe/engine pipe; 3. flex-pipe/engine pipe to fuel pump; fuel pump to the stock fuel filter (which mounts on the carb) are all open and without leaks. I have verified "open" by first blowing air thu them, and then blowing a tough cotten cord thru them, which I pulled back and forth to dislodge any crud. As noted before, the in-tank thru the sender unit was nearly blocked, and I thuroughly cleaned it. I have verified the lack of leaks by physical examination after putting air pressure in the tank.
2) When I first read Ray's comment about a clogged vent on the tank, I went to check the cap (there is a "vented" cap and no other vent), and discovered that the cap vent was indeed blocked. I replaced the cap with a new one, but that did not correct the problem.
3) The car has never just run fine at idle, but starved with an open throttle. When it gets fuel, it runs at any speed, but it will, eventually, begin starving for fuel and continue to starve to the point that it stops running and will not re-start.

When I first bought the car, it ran, but barely. One problem was that the acceleration pump was non-functional. At this point, I rebuilt the carb and gave it a general tune-up, and it seem to run fine. I discovered the starvation problem when I took it for a drive shortly after that work was done (in 1991). The fuel filter is the original cleanable unit. I have cleaned it, removing a lot of crud in the process. It may have at some time have had water in it, but there is a small drain screw provided for the specific purpose of draining accumulated water, and I cannot recall ever finding any water, or any water found was negligable.

The problem seems to be intermittant. Thus, when I first started the engine after its recent overhaul, I had not installed the gas tank, and so had it hooked up to a marine tank that was connected to the flex-pipe/engine pipe, and so to the fuel pump. When it initially would run on gas poured into the carb, but wouldn't keep running, I disconected the fuel line to the fuel filter on the carb, and tried again. Very shortly I had gas gushing from the line. I hooked the fuel line back to the carb and the engine ran until shut off with that arrangement. Just yesterday, after again verifying that gas was getting to the fuel pump (from the stock gas tank), and with the new vented gas cap in place, I started the engine using aerosol starting fluid, and with the fuel filter drain open. When running on the starter fluid, gas came from the fuel filter drain hole, in little spurts. But, when I closed the drain and kept running it on the starter fluid, but it never got enough gas to keep the engine running, even at idle. Last week, between these two events, I started the engine by pouring gas into the carb, finally was able to set the timing correctly, and shut it off. After about an hour of attending to other stuff, I started it up and was headed out of the driveway when it quit and would not restart. That is when I first posted this question.

As far as I can tell, the problem is not the fuel cap vent (anymore), the fuel tank (anymore), the fuel lines (anymore), the fuel filter (anymore), the carb (anymore), or water in the fuel (which is fresh with no ethanol). That leaves the fuel pump. I have not been able to do a pressure test as describe at sec. 3-15 of the manual as I have not been able to get the pump to fill the carb since the last time it quit, but the piddling production of fuel at this point suggests that the pump is not working right (though it may sometimes do so). I don't remember if I had my Buick Shop Manual when I rebuilt the fuel pump (in either '92 or '96), and so it is possible I mis-assembled it. I now have a second (never disassembled by me) fuel pump as well as the manual, and so I'm pretty sure I could do it right this time.

Ray-
I hope it is not (as you mentioned) a badly worn cam lobe. When I had the engine disassembled, I examined the cam generally, and found surprisingly (to me) little wear given the appearant 112,000 miles on the car. Of course, the cam may not be original, as I'm certain the head was at some time replaced with a salvage yard unit (tell-tale old yellow chalk mark on the rear of the head). I never "miced" any part of the cam as the engine had no valve train problems. It was in fact in operating condition, with no valve noise, though giving up some blue smoke through the exhaust. But, if the real problem is a worn cam lobe, how do I make that determination without pulling the cam? Or pulling the engine? The manual makes no mention of any test. Even if I set up a dial indicator, I cannot find any specs on the correct (or minimum) eccentric variation on the lobe to rum the pump. And, without specs, how could I determine if a pulled cam is in acceptable condition?

I cam buy a fuel pump kit for about $80, and a 6 volt electric pump for about the same. Certainly, if I have a bad cam lobe, I would buy the electric pump. Should I just buy the electric pump? This is not a show car.

'51 Special
 
If the cam lobe is worn enough to significantly reduce pump output, the wear will be quite visible. It usually appears as a groove worn in the high part of the lobe. You can see it easily if you shine a light in through the pump mounting hole. If necessary, turn the crank by hand to bring the high part of the lobe around to where you can see it. Please note that this is not a terribly common problem. I have seen fewer than a half dozen like this in 50 years of working on cars.

Intermittent problems are the hardest kind to fix. Again, just to make sure I am understanding your post correctly, are you saying that the engine will or will not run for an indefinitely long time on the marine tank?

Ray
 
Ray-

You know, I've probably never run it on the marine tank longer than 15 or 20 minutes at a time, and did so only for three reasons: 1) I started and ran it until it was warm last fall, because it had not run in nearly 10 years, and I wanted to know if it would run before I tore it down for a rebuild; 2) I started it after the rebuilt engine was in place and everthing was hooked up, but didn't time it then because I was running out of daylight, and I (correctly) suspected that I had the distributor installed a cog off; and 3) I also ran it a couple of times when I was trying to figure out why my generator seemingly was not charging.
.
Last week, when I first ran it on the installed tank, I did so to set the timing, and I allowed it to run about a half hour. During that time I also fiddled with the idle speed. I reved it a few times while doing these things, but it was idleing most of the time it was running. Then, later that afternoon, I started it to drive it, and and pulled away from the (tight) parking place, which required that I run it forward and reverse several times to inch it into position to get onto my driveway. Each time I changed gears, I reved it sufficiently to move it in gear. Only when I was slowly pulling onto the driveway did it begine to starve, and it quickly lost power and died.
The thing is, I had the day before dropped the tank, pulled the sending unit, and discovered it was completely or nearly blocked. (I may have blocked it completly where it has about a 60 degree bend by trying to push crud out with a soft copper wire, but before I started I couldn't blow thru it with lung pressure.) Once I got that mess cleaned out, I was pretty pleased with myself, thinking I had fixed a problen that had bedeviled me for 20 years. I thought I was going to go for a drive.

I had a similer feeling when I saw your suggestion about the tank vent, and found that the gas cap that had been on there the entire time was effectively not venting the tank. But by then I almost expected the disappointment when it came.

As for looking at the cam lobe when the engine is installed in the car, I kind of doubt that I will be able to get my head in the proper position. A mirror may help. Do you think I would be able to feel a groove worn on the high part of the lobe if the wear was sufficiently severe to keep the pump from performing correctly?

'51 Special
 
'51 Special said:
Do you think I would be able to feel a groove worn on the high part of the lobe if the wear was sufficiently severe to keep the pump from performing correctly?
Click to expand...

Oh yes, if the lobe was worn badly enough to cause a problem, you would definitely be able to feel the groove with your finger.

From your description of the engine's behavior, I am beginning to think the pump is to blame in some way. However, it's the intermittent nature of the problem that has me scratching my head. Normally, if a pump is bad, it's bad all the time, and that's all there is to it.

Since you already have a second complete pump, would you be willing to try it on the engine without rebuilding it? Check the lobe first of course. Before you connect the lines, hold your finger over the inlet port while you crank the engine. If you can feel suction, the pump is probably good enough to run a test with, assuming it doesn't have any external leaks. Just so you know, the majority of pumps get replaced because they leak either fuel or oil, not because they don't pump.

Ray
 
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Ray-
Thanks for the response.
I've been concerned because I long ago disassembled and rebuilt the fuel pump (in response to the problem I seem to still have) that I may have somehow misassembled it. Thinking about the (un)vented gas cap I replaced at your suggestion, and the crud I removed from the in-tank thru the sender unit part of the gas line, there is good reason to believe that the engine starvation I experienced when I first got the car, and what I'm experiencing now, might have different causes.
I just pulled the gas bowl and vacuum plate from my "spare" pump. In addition to replacing the cork gaskets for both, and cleaning its greasy and dirty exterior, I will have to clean lots of crud out of the gas bowl and the screen. All of that should be easily accomplished. The pump is off of a 1950 super that I bought to salvage parts for converting my '51 Special from Dynaflow to 3-speed stick. (As an aside, I thought this would be as simple as a similer job I did in 1964 on a '52 Belair. Boy was I wrong!)
The Super had sat outside with the hood off for maybe 30 years, but the only obvious reason for it being parked was a bent pushrod. And the water that got into the crankcase after someone pulled the manifolds was just enough to float the oil up to where it covered the crankshaft (and the rocker arm side of the pump) for the entire time. Every journal was shiney and nice when I pulled the crank after discovering they are different between the Dynaflow cars and the stick-shifts. I can't think of any basis in this history to condemn the fuel pump.
I will clean up and re-gasket the spare, pull the existing pump, check the pump lobe on the cam, and, if the lobe is OK, install the spare pump. I'll report back when done, whether or not it cures the problem. It might not happen immediatly. This is North Dakota, and I have to work outside. Forecast is good for Saturday, but ...
'51 Special
 
Ouch! I wouldn't wish winter in North Dakota on anyone I liked, especially for working on cars outside. Do you use an engine heater if you have to drive the car in winter?

If you've worked on old Chevys, you know by now that not all torque tubes are created equal. Chevy engineers got it right. Buick's must have had their heads up their collective asses. The Chevy clutch linkage is a lot friendlier too.

I'll be hoping to hear good news about the other fuel pump.

Ray
 
Ray-
Years ago I used engine heaters, especially for cars that had proved to be hard to start during warmer weather. I once had a '57 Chev with a power-pac 283 that had two 1200 watt "tank" heaters, one on each side, with outlets that plugged into the block through holes that had been filled with soft plugs. A half-hour of heat from that set-up, and it would not only start in -30 degrees, but the defroster immediatly put warm air on the windshield. But, I also once had a '56 Plymouth into which I had installed a six cylinder engine out of a '53. I left the six-volt starter on the engine, as well as the heavy battery cables from the older car. Twelve volts to the starter would spin the engine so fast it slowed to an idle when it lit off at -30 degrees. Eventually I learned that a tuned up engine and a good battery is just as effective, and a lot less trouble, than running an extension cord to the curb every night. And, with electronic fuel injection, if the engine will crank, it will start in any winter weather I have encountered in the last 25 years.
As to the Buick, I first verified that there was fuel in the line running to the side of the engine, and:
(1) Disconnected the fuel lines and cranked the starter to check for suction from the fuel pump it has had installed since I owned it. NO suction. I pulled the pump, and noticed that the fuel bowl was sitting cockeyed, no doubt from when I checked it for sediment a few days ago. I corrected that problem, cranked the starter with my finger on the cam eccentric lobe to verify it was not grooved, reinstalled the "original" pump, and again cranked the starter to check for suction from the fuel pump. NO suction. I reconnected the fuel line to the inlet side of the pump and cranked the starter. No fuel appeared at the outlet side.
(2) Cleaned and regasketed my "spare" pump. Cleaning the fuel bowl and screen produced over a teaspoon of very fine grit, but the vacuum end of the pump was quite clean and I did not further disassemble the pump. I bolted the spare pump to the engine and cranked the starter. NO suction. I connected the fuel line to the inlet side of the spare pump and cranked the starter. No fuel appeared at the outlet side.
For whatever reason, I have two fuel pumps and neither will pump fuel. The pumps are not identical. The spare pump is exactly as described in the Buick Shop Manual, and is also appears to be exactly as described in my 1956 Motor's Auto Repair Manual as an AJ Series AC combination pump. However, the pump that came with the car, also an AC combination unit, has a fuel section that looks the same, but the vacuum cover is very different. Because I have not been able to identify the model of the pump that came with the car, my current my plan is to have the spare pump rebuilt. It is, at least, a known AJ Series AC pump, and I don't need to risk the possibility that parts cannot be found for the unknown model. Your thoughts?
'51 Special
 
Your fuel starvation problem just keeps getting more and more mysterious. Now you've got me wondering if the pump is stroking at all, so I hope you don't mind running another test.

Remove the fuel cover and any loose parts that could get lost. Now crank the engine and watch what happens. If it looks like you are getting a normal stroke, then the problem has to be somewhere on the wet side of the fuel diaphram. If no or very little stroke, I would suspect
either the arm/cam interface or the linkage that connects the fuel diaphram to the actuating arm inside the pump.

Since you mentioned two different-appearing pumps, one of your pumps might be the 52-53 style. The two designs will interchange as long as you make the necessary adaptations on the vacuum side. This thread has pictures of both types:
http://www.teambuick.com/forums/showthread.php?21623-1952-263-Fuel-Pump

For identification purposes, all AC original equipment pumps were stamped on the edge of the mounting flange. Possible numbers are 529 and 7337 for the 51-earlier pump and 9761 for the 52-53 pump. There may also be other numbers for the early style, since the basic engine design dates from 1934.

Identification difficulties can occur with rebuilt pumps though, because rebuilders can and did use bodies from different applications. Many of these bodies are the same, with only the arms and covers being specialized for different engines. Responsible rebuilders would obliterate the stamped number if it was wrong and then ink stamp the correct number on the body or apply a paper label or attach a metal tag under one of the cover screws. Unfortunately, I have found several rebuilts where the stamped (now wrong) body number was still legible and the correct inked number had disappeared. Pumps like that can cause identification nightmares.

In case you are unable to identify the pump you have the kit for, or you find that it really is wrong, here is a correctly identified 52-53 pump.
http://www.ebay.com/itm/REMANUFACTU...Parts_Accessories&vxp=mtr&hash=item2a24b47e4f

Another vendor offers a rebuild kit for that pump and claims it is suitable for alcohol, so it might be worth the price he is asking if you find that the fuel in your neighborhood is attacking the rubber parts.
http://www.ebay.com/itm/1952-1953-B...Parts_Accessories&vxp=mtr&hash=item4abc9b0ac3

It sounds like you are more than experienced enough with cold weather starting to get through the winter without needing any help in that area.

As always, please keep us posted on whatever news (good or bad) you come up with.

Ray
 
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fuel issue

maybe you already did this but I did not read the whole novel. run clear line from the suction side to the pump and to the carb. if you see bubbles it is sucking air. is the fuel bowl staying full? also my car had a similar issue and I found a vacuum leak. spray that intake with some ether or carb cleaner. if it raises rpm pull the intake and reseal or use loctite 5920 and reinstall.
if all checks out get a FP from Bob.
is your timing 180* off?

stick with it. you will find the fix.
 
Ray-
You suggested running another test.

"Remove the fuel cover and any loose parts that could get lost. Now crank the engine and watch what happens. If it looks like you are getting a normal stroke, then the problem has to be somewhere on the wet side of the fuel diaphram. If no or very little stroke, I would suspect either the arm/cam interface or the linkage that connects the fuel diaphram to the actuating arm inside the pump."

Recall that i have two pumps, the one that came on the car (the "as-bought" pump), and one that came with a '50 Super I bought for parts (the "spare" pump). I ran that test with the spare pump installed. While I could only see the edge of the diaphram, it appeared to rise and fall about 1/4 inch. You didn't suggest what the normal stroke is, but I measured the full extent of the stroke that each pump is capable of. The spare pump can only travel about 3/8 th inch, and the as-installed pump has nearly 1/2 inch of travel. Assuming that the cam is not intended to move the pump through its fullest possible stroke, I assumed that the 1/4 inch movement is within the "normal" range. So, unless you advise that this is an insufficient stroke, thinking moves to the "wet side of the fuel diaphram.

I removed the fuel covers on both pumps.

The spare pump had a great deal of rust-colored powdery residue throughout the wet side of the fuel cover. I scraped most of it loose, and tapped the loose crud onto my bench, and actually measured to volumn to be slightly over two teaspoons, about half from the fuel bowl area, and about half within the fuel cover. The diaphram and valves were heavily coated with this crud. The wet side of the fuel pump was completely dry, and had sat without fuel for many years. The diaphram was stiff, partly because the metal part of the diaphram is quite large (at 2 3/8 ths inches, at least a half inch greater diameter than the as-bought pump) and the diaphram material is thicker and made up of 5 layers.

The as-bought pump was clean, with a residue of fuel. The valves were correctly assembled, and appeared intact and well-seated. The diaphram was intact and flexible, made of a single ply of fabric material with rubber-like covering on either side. The metal center of the diaphram was about 1 7/8 ths inch in diameter. The only odd aspect of the as-bought fuel diaphram was that the ten screw holes were elongated, with the elongation extending towards the center of the diaphram. On the dry side of the diaphram, some of these elongations extended virtually to the index mark made by the pump body flange, and to within 1/16th of an inch of the index mark made on the wet side of the diaphram by the fuel cover flange. The distance from the centers of the ten screw holes through the fuel cover flange to the inside edge of that flange is about 1/4 inch, meaning the typical elongation of the screw holes in the diaphram was well more than double the original diameter of each hole.

The crud in the spare pump could easily account for its failure to produce any noticable suction when the pump was onstalled on the engine and turned by the starter. But (unless the elongated screw hoes in the diaphram are significant), I cannot see any reason the as-bought pump failed to develop suction. Is it possible that the turning the pump with the starter moves in through a pumping cycle so slowly that any suction becomes un-noticable? I'd guess that the cam is rotating at less than 50 r.p.m. when the engine is being turned by the starter.

As to the type of ech pump:
(1) The spare pump is identical in every way to the exploded view of the fuel pump on page 89 of the 1951 Buick Shop Manual. That manual uses the same illustration as do the "fuel pumps" sections of my 1953 and 1956 Motor's Auto Repair Manuals, both of which refer to this as an AC AJ series combination pump. My 1956 Motor's Flat Rate and Parts Manual says the correct pump for 1949 through 1951 Series 40 and 50 Buicks is AC part no. 529. (This Manual covers only 49-56, so 1949 is not necessarily the first year for the 529 pump.) The spare pump appears to be identical to the one nali pictured with his 04-15-2012 post. However, the number stamped on its attachment flange is 9108. There is also a metal tag attached under one of the fuel cover screws and stamped with the number 2529. (2) The as-bought pump has a fuel cover identical to that of the spare pump, but a vacumn cover that looks much like the pictures of the 9761/9762, but clocked 90 degrees and fitted for steel vacuum lines rather than rubber. The number stamped on its attachment flange is R-7337. Just guessing here, but is the "R" in R-7337 an indication of a later replacement part that includes a later design for its vacumn cover?

All this said, I still have no confidence that I know what the fuel delivery problem is.

LONG

So far as I know, I have not have a vacuum problem or a timing issue. I did set the timing to factory specs a couple of weeks ago when I was actually getting fuel to the carb, and I know the timing is not 180 degrees off. (When I first installed the distributor after rebuilding the engine, I did get the distributor in a cog off. It ran, but barely. That has been fixed.) Right now, the engine runs only with primer or starter fluid, so I cannot check for vacuum leaks. If I did get it running, I'd proably wait to check vacuum, as it is only about 33 degrees in my open-air "garage."

'51 Special
 
Well, you really have me at a loss now. I can offer a few comments, but no real answers.

1/4" should be enough stroke to develop suction you can feel at the inlet port. The 50 rpm camshaft cranking speed should also be enough to develop suction.

The elongated screw holes in the diaphram are not normal, but I don't think they would cause a problem unless they extend beyond the inside edge of the flange on the cover or body. Btw, I think those may have resulted from failure to compress the spring before tightening the screws. You need at least three hands to do this, although I believe GM used to sell a tool to hold the rocker arm in the compressed position.

As for the actual problem, I think you may be onto something with the valves. Two teaspoons worth of crud in the spare pump would certainly do it. On the clean pump you can test the valves by blowing or sucking through the ports backwards. That is, blow through the outlet and suck on the inlet. Both of them should seal tightly. If you feel any leakage, there's your problem.

It looks like you caught the typo I had in my previous post. 9761 is the correct pump for a 52-53 263. 9762 belongs on a 320. I have already fixed the error.

Your spare pump is a good example of what I was talking about earlier regarding parts substitution on rebuilts. I would feel better if I could find a second confirmation on the 9108 stamping, but there is a good chance that body may have started out in life on a Hudson. The rebuilder tag will always overrule the stamping in a case like this. I have no idea why it says 2529 instead of 529, though.

As you correctly figured, 7337 is a replacement pump manufactured after AC discontinued production of the original type vacuum cover. However. I think the "R" on your example could also indicate that the pump was commercially rebuilt at some point.

I sure hope you find a bad valve in the clean pump, because I am running out of ideas here.

Ray
 
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Ray-

You observed: "On the clean pump you can test the valves by blowing or sucking through the ports backwards. That is, blow through the outlet and suck on the inlet. Both of them should seal tightly. If you feel any leakage, there's your problem."

I tried this test. Here are the results:
Blow on the inlet: easily done, can hear the valve warble;
Suck on the inlet: harder to judge, but I can move some air, and the air tastes of gasoline;
Blow on the outlet: cannot move any air;
Suck on the outlet: easily done, can hear the valve warble.

This seems to be the "aha" moment.

Last question. With two pumps, each apparently needing to be rebuilt, do you think the wiser course is to rebuild the clean pump (even though it is not original equipment), or the severely grungy pump (plainly original equipment)? This is a driver, not a show car, but I have tried with all of the many repairs to use parts that were correct for a 1951 Special. I expect to have the chosen pump rebuilt by a pro.

'51 Special
 
'51 Special said:
This seems to be the "aha" moment.
Click to expand...

Finally! After all this time, maybe, just maybe, a little bit of progress. Of course we still don't know why the engine will sometimes run with the as-bought pump. Nonetheless, a bad valve is a bad valve, so I think you are on the right track with the rebuild.

As to which one gets rebuilt, neither of the pumps is technically original equipment. 9108 is clearly a rebuild (on a Hudson body, yet!), and I kind of suspect that 7337 may also be rebuilt. However, I feel the same as you about using parts that look like they could have been installed at the factory, so 9108 is the big winner.

How do you plan to select a rebuilder? I can't offer any suggestions, as the last one I had any personal contact with closed its doors some years ago.

Ray
 
Ray-
Thanks for all of your help and patience. Did you ever teach?
I have posted an inquiry asking about rebuilders on the BCA site. No rebuilders locally, so I may do some on-line research. And, as I'll be in southern California this January, I may be able to find a shop that I can visit.
'51 Special
 
No, I have never taught any classes. Most people who know me well would probably say I don't have the patience for it, and I would tend to agree with them. Thank you for the compliment, though.

Cars have been my hobby since I was about 14, but I have never worked on them professionally. I was a mechanical engineer until I retired a few years ago, and I worked in the parts business when I was younger.

Escape from ND to southern CA in January? Good choice!

Ray
 
Ray, I was in the parts buisness, too, and travelled in ND in the Winters. Stranded in Bismarck many times. Escaping in January, "Smart" choice.
Doug
 
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