Zenith Accel. Pump Plunger Assy. Sold In Classifieds: Feedback?

[Brian R Adams]

Guys,

Thanks to all!

WRT the pump nozzle, I decided not to remove the clogged one, but rather first attack it in situ. The inlet hole (towards the jet) will not accept a 0.060" pin gage, but did take a 0.059" gage, which I used to chase the channel right through the nozzle, passing by the outlet orifice along the way, and this dislodged whatever was clogging it, and immediately equalized the issue from the two nozzles. (I seem to keep finding uses for my vast collection of pin gages.) Both now stream fuel down at the same angle, and without any spray dispersion (as the clogged one had been.)

I will summarize my work on the pump wells, and the linkage settings I settled on, a little later.

Brian

[Ron LaDow]

[...]
Thanks, Ron and Gary, and all the others for your discussion; it helped tremendously.

Vic,
Pretty rare when any of us *CAN* help you, but you're more than welcome.
Vic (and others): Just did a finger count.
In early 1968 I swapped a 122S (warm, dry, quiet) Volvo sedan for a late '55 Speedster which had a top frame, but no top. Turned out to be one of the wettest recorded winters in Bay Area history.
Didn't learn much about 356s that year, but I learned if you didn't go on dates for a while, you could afford a top (and no one wanted to go on dates with a guy who had no top on his car). I got the top about when the rain stopped...

[Brian R Adams]

Fellas,

I devised the perfect collection device for measuring pump output! I tried Ron's folded soda straw, but the straw when folded is too fat to fit easily down into the venturi and position under the nozzle without distorting the straw. There had to be a better variation. Here's what I came up with:

It so happens a straw from 7-Eleven has a 1/4" ID. And a typical wooden pencil's eraser is 1/4" in diameter - perfect stopper for one end of the straw.

Now, 0.3 ml is 0.0244 in³. It turns out the height of a cylinder of diameter 1/4" (0.125 radius) and volume 0.0244 is exactly 1/2". So after positioning my rubber stopper, I marked 1/2" on the straw using an extra fine point Sharpie.

Finally, I cut a notch in the straw about 1/2" above the 0.3 ml mark to slip easily over the pump nozzle, using a 1/4" wooden dowel to support the straw while slicing with an Xacto blade. (The dowel also helps square up the stopper inside the straw.)

Works like a charm! The stopper fits tight enough not to leak gasoline, and the rig is slender enough to position and withdraw without fuss.

Brian

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[Brian R Adams]

WRT pump nozzle:

I did remove it, as it was lagging somewhat behind the output from the other side. I ran pin gages through the inlet and discharge orifices, but it still lagged. Then I swapped the metering jets (both marked "40") and, lo and behold, the problem followed the jet! Those are easy enough the remove, gage, and unplug, but nothing I do gets the lean jet to come up to scratch. However, using my new discharge capture gage, the "lean" side comes just up to the "0.3 ml" mark (top of meniscus), and the "rich" side is just over the mark (bottom of the meniscus) so we're only talking a 1/16" or less difference. (In the other carb, both sides measure to the same level.)

I decided to stop chasing the issue, and run the carb this way, with slight imbalance between the accel. pumps.

Brian

[Brian R Adams]

Update:

I ordered Ron's Zenith fuel level gauge, and it works great. My fuel levels are spot on, and do not change perceptively between idle and high revs. So my fuel pump seems to be working fine.

The reason I have no power driving the car is I have a dead bank of cylinders. The passenger side (#1 and #2) cylinders do not respond to changes in the idle mixture screws, even closing them completely! When I disconnect the spark cables, neither #1 or #2 affect idle speed at all. Yet, I am getting good spark at both cylinders, with new plugs.

I don't understand how both idle jets in that Zenith could be plugged up. I had all the jets out on the bench, and verified they are open. I suppose both idle bores could be plugged up in the carb base. I guess I'll have to go through it on the bench again, but it does seem odd both #1 and #2 circuits are plugged. As for the driver's side, both #3 and #4 respond well to even slight idle mixture screw movements.

The only other thing I can think of would be the intake valves not opening in that head. I'm letting the engine cool down to check valve lash, but it hasn't been many miles since I checked them, and this problem came on suddenly. Or I have lost all compression on the bank of cylinders?

Any thoughts?

Update: Didn't yet check valve lash, but ran a compression test on #2 cylinder (one of the "dead" ones): 110 lbs.

So it's not loss of compression (rings scoured down somehow). Could still be intakes never opening, I suppose.

Brian

[David Jones]

Brian, can you measure the temp at the exhaust manifold outlet with an IR gun? If you increase the idle on the dead side does the temp suddenly increase? Many years ago I had the same symptoms and it turned out that the butterflies were fully closed so no air or fuel was getting to the cylinders. A half turn on the idle screw (not the mixture screw) and suddenly everything was working. If you want to eliminate the cylinders as the problem just swap the carbs over. Worry not about the linkage if all you want to do is get it to idle.

[Brian R Adams]

Brian, can you measure the temp at the exhaust manifold outlet with an IR gun? If you increase the idle on the dead side does the temp suddenly increase? Many years ago I had the same symptoms and it turned out that the butterflies were fully closed so no air or fuel was getting to the cylinders. A half turn on the idle screw (not the mixture screw) and suddenly everything was working. If you want to eliminate the cylinders as the problem just swap the carbs over. Worry not about the linkage if all you want to do is get it to idle.

Very interesting, and easy enough to test (yes I do have an IR gun). But I have been playing with the idle speed screws, and it would surprise me if this was the problem. If the butterflies turn out to not be closed, I will probably then swap the carbs anyway, just to prove it's purely a carb problem.

I recall reading a rebuild article wherein it was recommended to adjust (before installing carbs) the idle stop screw with a .003" feeler propping the butterflies open, as a baseline position.

Brian

[Brian R Adams]

David, pondering further tonight: I see how your suggestion would address a dead bank at idle, but the problem persists well off idle, butterflies open. At idle it manifests as a steady but rough idle. With throttle open to commence driving (but still partially in the idle circuit) it manifests as falling on its nose, i.e. no torque. Also I get some backfiring.

Brian

[David Jones]

Brian, backfiring indicates a lean condition so maybe there is a problem with the carb base so you can also try swapping them over. A bad gasket between the two could also leak air into the idle circuit and that would nullify any attempt to alter the mixture flowing into the carb manifold. Imagine the size of the jet and then the surface area of the carb to base interface and it is apparent that even a couple of thou air leak path would weaken the mixture by a vast amount.

[Brian R Adams]

Brian, backfiring indicates a lean condition so maybe there is a problem with the carb base so you can also try swapping them over. A bad gasket between the two could also leak air into the idle circuit and that would nullify any attempt to alter the mixture flowing into the carb manifold. Imagine the size of the jet and then the surface area of the carb to base interface and it is apparent that even a couple of thou air leak path would weaken the mixture by a vast amount.

I'm pretty sure the base-to-body seal is good, but good point. The gaskets are in great shape, and I previously (on someone's suggestion) used a black Permatex gasket sealer to stick the gaskets to the carb bodies, so only the base sides break free readily. I will inspect the seal there nonetheless. One could introduce some cigar smoke near that joint while the engine idles, to see if any smoke gets sucked into the joint.

I think there is a slight amount of fuel getting through the idle circuit, on one side only (its mixture screw has a very slight effect on idle, the other side none at all) so that would create a lean condition, and could account for the occasional popping.

(I should also have mention I had used the hand throttle to produce a higher idle - opening the butterflies a bit - and twiddled the mixtures screws, so in that scenario, no butterflies were closed.)

TBC ...

[Brian R Adams]

Anyone know where to get the tiny plastic (fibre?) seal inside the accelerator pump outlet valve? Mine is weeping fuel, the seal is intact but somewhat distorted and less than ideal. I was a bit dismayed there was not replacement inside my Walker rebuild kit.

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Brian

[Ron LaDow]

Brian,
Don't take those valves apart (I think that was on page one of the rebuild article from years ago). You can get them clean assembled and that gasket is simply not available.
But it is fixable. Clean the parts with that stuff you use to get the shower tile clean; most of them will make the bras shine. Put the spring and plunger back in, wipe some epoxy around the periphery of the piece with the male threads, put it together and give it overnight.
If all else fails, check with NLA/Stoddard; I haven't looked in a while but they offered new ones.

[Brian R Adams]

Brian,
Don't take those valves apart (I think that was on page one of the rebuild article from years ago). You can get them clean assembled and that gasket is simply not available.
But it is fixable. Clean the parts with that stuff you use to get the shower tile clean; most of them will make the bras shine. Put the spring and plunger back in, wipe some epoxy around the periphery of the piece with the male threads, put it together and give it overnight.
If all else fails, check with NLA/Stoddard; I haven't looked in a while but they offered new ones.

Well, it was weeping, so I had to take it apart. I'll probably epoxy it closed as you suggest.

Here's NLA's new item:

http://www.nlaparts.com/store/zenith-pu ... 22513.html


Also, Swiss Army Vehicles offer one, but they posted the wrong photo (not unusual for them - the description is probably correct):

https://swissarmyvehicles.com/haflinger ... th-ndix-32
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[Ron LaDow]

Brian,
The 36mm carbs got continuing development and the 36 A/P 'exhaust valve' is improved over what we have (like the A/P plunger), but like the plunger, it's the wrong size.
It's been a while so I can't remember which, but it is far enough off, big-or-small, to preclude output adjustment to our spec.

[Brian R Adams]

Brian,
The 36mm carbs got continuing development and the 36 A/P 'exhaust valve' is improved over what we have (like the A/P plunger), but like the plunger, it's the wrong size.
It's been a while so I can't remember which, but it is far enough off, big-or-small, to preclude output adjustment to our spec.

I was aware of that pitfall, but the valve I linked to is specifically for 32 NDIX (and the only part they still sell for it!) They do sell a plethora of 36 NDIX), here's their pump pressure valve for 36 NDIX:

https://swissarmyvehicles.com/pinzgauer ... valve-carb

Or did you try their "32 NDIX" valve and find it to be wrong as well?

Update: Do NOT waste money on the Swiss Army Vehicles pump pressure valve. They simplified (cheapened) the design, and from simple inspection I don't believe it will work well if at all. But also, the two I received had damaged threads. One I rehabilitated easily enough, but called SAV to get a replacement (free) for the other one, but they sent me an obvious old, used item! So stick with the NLA / Stoddard replacement part (linked to previously).


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