Zenith Carb Question(s)

[Brian R Adams]

Thanks Brian - not sure where I"ll find the star washers but will certainly try.

The new accelerator pump is moving nicely in the now clean carb body - I thought I read the skirt should be soaked in gasoline before use? Any words of wisdom about that?

If Stoddard / NLA doesn't have the correct German style star washers, an Ace Hardware store will have a selection of generic ones in various sizes, you'll probably find some close enough to work. Ace sells them by the piece, not in sealed packages.

The reason to pre-soak the leather is to have a proper seal while adjusting the pump output volumes. Eventually the carbs in use will probably sit long enough for the fuel to evaporate out of the carbs, and the leather will shrink a bit. Then it takes a little while for the leather to swell again when putting the car back on the road. You want the pumps to have been adjusted for the operational state, not the dry startup state.

Most guys I've asked attach the pump actuator/adjustment rod in the hole nearest the end of the pump arm. To increase pump output, shorten the rod; to decrease output, lengthen it. A starting rod length to try is 3", but each carb will need its own particular length, it's purely trial and error to find out. One approach is to shorten the rod down as far as it can go, then start lengthening it, a full turn of the turnbuckle adjuster at a time, reducing the output until you are down to the 0.3cc for 2 strokes.

If you are not getting very close to the identical output volume from both nozzles inside a carb, it means one of the nozzles or its associated metering jet is somewhat blocked by crud. The tiny squirt hole on the underside of the nozzle is only about 0.011" in diameter.

Here's a simple tool I came up with for capturing the gas squirted out of the pump nozzles. It's a segment of plastic straw from 7-11 store, and a segment of a common pencil eraser for the bottom stopper, sealed into place with CyA (super) glue. The ID of the straw is 1/4", and the black mark is 1/2" above the stopper, marking the 0.3cc level. The notch in the straw (cut with a sharp Xacto blade) fits over the pump nozzle. You lower the tool down alongside the nozzle, then shift the notch sideways to enclose the nozzle. The gas will squirt down towards the stopper. Withdraw it after pumping two squirts into it for examination. Don't be in a hurry - when properly adjusted the gas from a full stroke of the throttle lever takes a second or two to stop flowing. Open the throttle fully, hold it open for say three seconds, let the throttle close, and repeat. Then see how much the tool captured.

When done using it, I slip a length of 1/4" wooden dowel into it to keep the straw cylindrical when not in use.

20190603_124008.jpg (2.16 MiB) Viewed 2288 times

[Ken Tuvman]

Great info Brian - like your creativity on the bench set up using the bulb from an outboard motor hose & the straw above - one of the carbs was particularly contaminated with old fuel and kept getting a bunch of white powdery stuff - have soaked bodies in carb cleaner and gently using a scotch pad to get the crud out after air blowing everything dry - all passages and jets are now open!

I noticed the mating surfaces from top of carb that goes to manifold have some light marks - what is the proper technique for block sanding the surfaces? I have glass on hand and also a quartz counter top - thinking if I can slip a piece of paper under the surfaces (top of carb to bottom of glass) than my surfaces are not flat. Plan to use 400 black sandpaper or also have emory paper.

[Brian R Adams]

I noticed the mating surfaces from top of carb that goes to manifold have some light marks - what is the proper technique for block sanding the surfaces? I have glass on hand and also a quartz counter top - thinking if I can slip a piece of paper under the surfaces (top of carb to bottom of glass) than my surfaces are not flat. Plan to use 400 black sandpaper or also have emory paper.

You'll need to rephrase the question. The "top of carb" is nowhere near the (inlet?) "manifold" (which mates to bottom of carb).

Brian

[Ken Tuvman]

bottom

[Ron LaDow]

Avoid spending time where it does no good:
1) The cast iron throttle body is "flat" on both top and bottom within any meaningful use of that word; don't waste any time on it other than cleaning the surfaces.
2) Ditto the bottom of the Zn float bowl casting.
3) Further, do not waste time making the top of that casting or the mating surface of the cover 'perfectly' flat; doesn't matter. The fuel which addresses that joint is splashed up from close to 3/4" below that surface and given the thickness of the current gaskets, tightening the cover screws simply warps the top cover surface again.
Spend time getting the float platten area square to the float valve pin at the proper fuel level, so your adjustments get close to the calc'd changes. If you go from too high to no fuel at all, it's a geometry issue; there is an article somewhere in the archives dealing with that.
And then, spend the time getting the jet cover female thread normal to the gasket surface to keep from leaking there.
I hope to have a 'solution' to the continuing accel pump piston problem sometime in the next month or so. Or so...

[Brian R Adams]

Ron, do you find the Walker kit's pistons are to be flawed? I did find I needed to trim about 1/16" off the end of the short 90-deg portion that goes through the pump lever arm inside the carb top cover. There's not much elbow room in that recessed area, and it wanted to bind.

The leather does seem archaic and suboptimal for consistent metering. It occurred to me some time ago it would be easy to adapt the SwissArmyVehicles "too short" piston w/ a polymer seal for our carbs. Just cut the rod in the middle and use brass tubing to fashion an extension. Either solder or epoxy the tube in place. Voila!

Brian

[Ken Tuvman]

Thank You Ron & Brian - now that carb bodies & jets are clean& clear my focus will be on correctly setting floats & accelerator pump.

About how long should I soak AP skirts & others have suggested
Gas or light oil.

Also - any point in using a product like permatek between
Paper gaskets & mating surfaces? ( just a light coat?)

[Don Gale]

About how long should I soak AP skirts & others have suggested
Gas or light oil.

Also - any point in using a product like permatek between
Paper gaskets & mating surfaces? ( just a light coat?)

If using gas, it will soak in quickly, maybe only a few minutes. You will see it change color and darken. The heavier the oil, the longer it will take. You could make a small batch of 2-cycle gas/oil blend, say 30:1 and it would be more than sufficient, or even gas & ATF.

NO on using gasket cement of any kind, don't risk excess cement finding its way into the jets or cause the float valve to stick. Installing the gaskets dry will let a little gas soak into the paper and allow them to swell slightly, making a better seal. I like to smear a very very thin coat of vaseline on the aluminum faces and use the paper gasket dry. This allows for a slight amount of squirm and lets the mating parts find their "home". Lightly tighten the screws in a criss-cross pattern and don't snug them until they are all nearly tight, tightening in numerous iterations.

If you do feel the urge to use Permatex or such, only use it on the aluminum washer on the center bolt on jets side cover.

[Ken Tuvman]

Thank You Don!

[Alexis Collaud]

Hello,
In the same Zenith ndix carb rebuilding process, I have a dummy question : how do you dismantle the accelerator pump to change the red seal ?
here is what I have :

repair-kit-accelerator-pump-zenith-32-ndix-356a-356b-356c.jpg (8.53 KiB) Viewed 2144 times

the pump :

s-l1600 (2).jpg (31.52 KiB) Viewed 2144 times

[Ron LaDow]

Ron, do you find the Walker kit's pistons are to be flawed? I did find I needed to trim about 1/16" off the end of the short 90-deg portion that goes through the pump lever arm inside the carb top cover. There's not much elbow room in that recessed area, and it wanted to bind.

Haven't 'done' carbs in while, so I'm not familiar with the current kit suppliers. Going out on a short limb here and guessing that all the pistons come from the same supplier and if they exhibit any constant characteristic, it is inconsistency. Speaking with a pro late last week, he mentioned the frustration of getting one that 'came in' after minimum fiddling and the other which only took him a week one day... And then didn't deliver the same the next day.

It occurred to me some time ago it would be easy to adapt the SwissArmyVehicles "too short" piston w/ a polymer seal for our carbs. Just cut the rod in the middle and use brass tubing to fashion an extension. Either solder or epoxy the tube in place. Voila!
Brian

I've looked at that, and it might work, but the labor costs are such that it's not a realistic "product" which Pre Mat could expect to sell.

[Ron LaDow]

Hello,
In the same Zenith ndix carb rebuilding process, I have a dummy question : how do you dismantle the accelerator pump to change the red seal ?
here is what I have :
repair-kit-accelerator-pump-zenith-32-ndix-356a-356b-356c.jpg
the pump :
s-l1600 (2).jpg

AFAIK, those parts are factory-assembled by crimping; I know of no way to replace one 'skirt' with another. Nor is there any reason to believe it would be an improvement if you could: A good used one is certainly preferable to a bad new one.

[Brian R Adams]

Haven't 'done' carbs in while, so I'm not familiar with the current kit suppliers. Going out on a short limb here and guessing that all the pistons come from the same supplier and if they exhibit any constant characteristic, it is inconsistency. Speaking with a pro late last week, he mentioned the frustration of getting one that 'came in' after minimum fiddling and the other which only took him a week one day... And then didn't deliver the same the next day.

Having just gone through my own plus a friend's Zeniths, I agree wholeheartedly that nailing down the pump outputs is an exercise in herding cats, and that's with brand new Walker pistons w/ nice leather skirts. I'm now dead set on adapting my S.A.V. polymer-cupped pistons for use, as I described. I figure that JB Weld will hold it together in a gasoline environment.

But another source of inconsistency could be the pump pressure valve. As designed, the OEM valve relies on a brass-on-brass shut-off and a cute but delicate little spring. I wonder if the spring after 60 years is adequate for the task?

Brian

[Bruce Smith]

The solution is pretty simple, and I've done a lot of them (hundreds). I usually use Walker kit pumps and have only had a couple that were difficult to seal. First make sure the pump cylinder in the carb housing is clean and smooth. If it's pitted, which is rare, you're going to have problems and probably will need a new body. If needed, run a brass small brush or a some Scotch-brite inside the cylinder but don't overdo it. Clean it and dry it good (no oil, WD-40, etc.) Then expand the skirt of the dry leather sheath of the new pump just a little bit, again don't overdo it. When you insert the pump, guide it squarely into the cylinder to ensure that it goes in evenly all around since you've expanded it's skirt. Insert it dry, i.e. no oil, gas, or solvent. Then do the set-up up on a bench with mineral spirits to adjust float level and pump volume. Wait a few minutes after you've filled the bowl so that the pump sheath is sufficiently wetted. Then manually work the pump through its full stroke with the pump rod disconnected until it begins to squirt from both injectors. Problems can arise if you haven't cleared and gauged the pump jets and injectors, ensured their seats are clean and smooth, and installed new pump jet o-ring seals. Once they're squirting, connect the pump rod to measure volume. A good starting length is 70mm. Longer is less volume shorter is more. I use a syringe to fill the bowls - I wrote a Registry article a while back on the set-up.

[Ken Tuvman]

Thank You Bruce - would love to see a link to your story and read it.