Square Top Carburetor Questions

[Matt Wilson]

Hi All,

I'm rebuilding the carburetor in my '49 Power Wagon, which I believe to be one from the E7 series, based on the info at the T-137 website, though not sure which E7, since the tag is long gone.

Anyway, I searched and found several related threads here on Gordon's site. I read with interest the thread below which provides descriptions and pics of the various accel pump springs that can be put in the square top carbs.

http://www.powerwagonadvertiser.com/...uretor+gaskets

I don't know if my carb has its original/correct spring or not, so I measured the free height and the spring force at a 1/2" compression as described in the thread. The free height is 1-7/8" - all good there. The spring force appears to be about 22 - 23 oz, which is much lower than the 40 oz recommended in the thread, and even low compared to the 30 oz said to have been supplied for higher altitude operations. The color seems to be someting like you see when a steel part is cad plated (silver but with a light red-yellow tint). I also have two round top carbs, and I measured the spring height and force at 1/2" compression. Heights were both 1-7/8", but spring forces were about 32 - 33 oz in one, and 42 - 43 oz in the other. I believe the colors are siliver and bronze/copper, respectively.

As best I recall, the truck seemed to run ok with this carb setup the last time I used it, except that there was always a slight hesitation upon acceleration, which I had heard was pretty normal for the vacuum advance carbs. I've been using a later model round top carb for a few years, but thought I'd try out the square top unit again.

Since removing the spring is somewhat of a pain in the square top carb, I would like feedback from others on whether I should swap in the spring from one of the round top carbs, so I hopefully just put in one spring and be done with it. Also, if there is another way to replace the spring in the square top carb, I'd like to know it. I had to gently drive out the pivot pin that connects the accel pump to the brass vacuum piston. It's not hard, just takes more time and there's always potential for damaging the piston or the accel pump.

Couple other questions:

Should I use any kind of oil, grease, sealant on the carb gaskets? I never have in the past, but thought I would ask if I should be, or if it would keep them alive longer. I'm having to make my own gaskets, by the way.

Also, how much radial play is acceptable in the throttle shaft? When I grasp the throttle plate and shake it radially, it has what seems to be very little play, but I haven't measured it. Maybe it's supposed to have no perceptible play?

Thanks,

Matt

[Gordon Maney]

Hi All,

I'm rebuilding the carburetor in my '49 Power Wagon, which I believe to be one from the E7 series, based on the info at the T-137 website, though not sure which E7, since the tag is long gone.

Couple other questions:

Should I use any kind of oil, grease, sealant on the carb gaskets? I never have in the past, but thought I would ask if I should be, or if it would keep them alive longer. I'm having to make my own gaskets, by the way.

Also, how much radial play is acceptable in the throttle shaft? When I grasp the throttle plate and shake it radially, it has what seems to be very little play, but I haven't measured it. Maybe it's supposed to have no perceptible play?

Thanks,

Matt

No grease or sealant. Over the years I have made numerous carburetor gaskets. Use something like Victor gasket paper and you will be fine.

Regarding the clearance, you would like to have as little as possible. A test can be how it idles and what effect it has when you shoot something like WD40 on the end of the shaft while it idles. If the speed changes, there is too much clearance.

The vacuum accelerator pumps are more hesitation prone than the mechanical ones, simply by virtue of how they work. It is a reactive circuit/system, not a proactive one like the mechanical system.

Let's see if someone else weighs in on what the correct spring should look like. I am thinking Clint Dixon or Dave Langford may know.

[Doc Dave]

Matt,
Clint is more knowledgeable on this than I am, but what you are saying seems logical to me. Also I like Gordon's take that a square top is a reactive system by design with acceleration.
From what I have learned the vacuum accelerator pump system is inherently prone to a slight hesitation. I have become used to mine so it does not bother me.
Did you check out, in Joe's forum's "best of the forum", "square top carburator secrets". I added that over there after good input from Bob Jones and Vaughn Payton, along with my saga of trying to get mine to function.
When one gets the VPW rebuild kit, you use everything EXCEPT the old "weaker" spring and older accelerator pump shaft and leather.
THe spring in the kit is too stiff, and the provided acc pump shaft is wrong.
I would be tempted to leave yours alone.

[Matt Wilson]

Thanks to you both for the replies! Doc Dave, I took your suggestion and just now checked out the "Square Top Secrets" on Joe's forum. Lots of great tips! One good take-away from that is that I will check out whether I need to hone the bores where the piston and pump go.

I'd still like to get someone's input on which spring I should use, of the three that I have available. It's probably been around 15 years since I've had this carb apart, or driven the truck with this carb, and I can't recall if I put the old spring back in it at that time or not. Since my foggy memory says the truck drove ok with the current spring, I may just put it back in the carb and go with it, but since the other thread I linked in my first post says 40 oz is the correct one (and mine is only about 22 oz), it makes me wonder if better performance could be had.

Another question while we're at it: Is there supposed to be anything like a gasket or an o-ring between the "tube" on top of the carb and the air cleaner housing that it fits into? Seems like that's a potential pathway for dirt to enter the engine.

Thanks again!

[Clint Dixon]

Thanks to you both for the replies! Doc Dave, I took your suggestion and just now checked out the "Square Top Secrets" on Joe's forum. Lots of great tips! One good take-away from that is that I will check out whether I need to hone the bores where the piston and pump go.

I'd still like to get someone's input on which spring I should use, of the three that I have available. It's probably been around 15 years since I've had this carb apart, or driven the truck with this carb, and I can't recall if I put the old spring back in it at that time or not. Since my foggy memory says the truck drove ok with the current spring, I may just put it back in the carb and go with it, but since the other thread I linked in my first post says 40 oz is the correct one (and mine is only about 22 oz), it makes me wonder if better performance could be had.

Another question while we're at it: Is there supposed to be anything like a gasket or an o-ring between the "tube" on top of the carb and the air cleaner housing that it fits into? Seems like that's a potential pathway for dirt to enter the engine.

Thanks again!

Matt, I have always used Permatex High Temp copper colored spay gasket adhesive on all my carbureter gaskets. I don't know if it makes them seal better or not, but the next time you take it apart, the copper coat will keep the gasket from sticking to both surfaces and tearing into pieces.

I have rebuilt a lot of square top carbs, but have never replaced a spring. Having never had a kit with the spring included, I just use the old one over again. I have never experienced one that seemed to be weak with age. Maybe I have just been lucky?

Yes, there is a gasket between the carb "tube" and the air cleaner. They are usually rock hard and stuck in place.

[Matt Wilson]

Thanks, Clint. That is an interesting idea, using copper spray sealant. I will try it out.

I can't recall if the last kit I purchased (some 15 or more years ago) came with a spring or not. The one in the carb now might be from a kit or might be original. I can't recall. If I don't hear back from anyone else with a definitive answer on which spring to use within the next few days, then I'll just put it back together with the spring that's in there now. If I find acceleration is a problem, then I may try swapping springs and see what happens, and I'll post here to let you all know.

As for the gasket between the "tube" and filter, can you describe what it looks like? My manual doesn't seem to have any kind of image of it, and my setup has never had it in the 21 years that I've owned the truck. Is it a gasket at the top of the tube, like an o-ring where the tube fits into the lip of the filter inner diameter? Or is it more like a gasket that wraps around the outside of the tube to take up the space between the tube and filter?

Thanks.

[Clint Dixon]

Thanks, Clint. That is an interesting idea, using copper spray sealant. I will try it out.

I can't recall if the last kit I purchased (some 15 or more years ago) came with a spring or not. The one in the carb now might be from a kit or might be original. I can't recall. If I don't hear back from anyone else with a definitive answer on which spring to use within the next few days, then I'll just put it back together with the spring that's in there now. If I find acceleration is a problem, then I may try swapping springs and see what happens, and I'll post here to let you all know.

As for the gasket between the "tube" and filter, can you describe what it looks like? My manual doesn't seem to have any kind of image of it, and my setup has never had it in the 21 years that I've owned the truck. Is it a gasket at the top of the tube, like an o-ring where the tube fits into the lip of the filter inner diameter? Or is it more like a gasket that wraps around the outside of the tube to take up the space between the tube and filter?

Thanks.

It is a gasket that is up inside the filter. It does not appear to be an O-ring, or even to have a round cross-section. It appears to have a rectangular cross-section and may be leather rather than paper. I am afraid to pick at one to get it out as it may fall apart and I know I have nothing to replace it.

[Matt Wilson]

Thanks again, Clint. I looked up into the air cleaner tonight and could see a lip where a gasket once could have been, but I don't think there is much or any of it left on mine. I think one could find an o-ring to fit in there, though, so that is what I will try to do.