Zenith 40 TIN Accel Pump Help

[rapidag]

I have done a rebuild of my Zenith 40's for my 1971 911T (2.2L). After rebuilding, the right side accelerator pumps do not work at all.

Looking at a good breakdown of the carbs I am wondering if the accelerator suction valves are missing a check valve, or a ball to check flow when the diaphragms are pushed in.

Positive displacement pumps, piston pumps, diaphragm pumps, compressors, etc... always have a suction and a discharge valve. The discharge valve (ball type) appears to be in the injection tube (part #25 in the maintenance manual) , however the pump inlet valve (item #26) does not seem to have any type of valve. It looks like a jet that is screwed into the bottom of the float bowl, but I can not see any type of check or ball in it.

Does anyone have experience with the accelerator pump inlet valves? When I filled the bowls with gas on the bench-top and pumped I could see flow flowing back into the bowl, not down the throat of the carb.

New inlet valves? Bad reassembly? Bad luck??? I really need some help figuring this out.

As a side note I am going to miss a Loma Prieta PCA event this weekend I have already paid for (food, lodging, etc...) and would gladly hand it over to another enthusiast for 1/2 price... ($100) They are going to the 17 Mile Drive in Carmel, then overnight near Mission San Juan Batista.

If interested in the trip, please let me know. If interested in giving advice on the carbs, please do!!! I have got to get this thing running again!!!

Thanks,

Mike

[1QuickS]

Each throat has a squirter with glass ball check valve and a supply check valve in the fuel bowl with a glass ball, again. Unlike the Weber carbs that depend upon all check valves to be working equally well; the Zeniths may experience one squirter not working correctly while the other two perform fine. I have serviced two sets of the Zeniths with one more on my bench at this time and have decided to stop offering service for these as I was having difficulty making the check valves work and I don't have a source for new replacements...

If the check valves cause an obvious swirling in the fuel bowl when the throttles are opened then you have a faulty check valve and you will not be able to get the squirt qty right. Also, if the o-ring on the squirter body allows fuel to bypass the seal then you will have a poor shot due to that. The check valve in the squirter keeps the fuel from draining down into the bowl so if that one is defective then the fuel will need to replenish the lost fuel in the vertical fuel supply gallery before the squirt begins.

Of course if check valves have been replaced with jets then it won't work at all as you opined.

[James Brown]

Check the squirter tubes to see if there plugged up, there quite small but there still available for about $ 60.00 each!

[rapidag]

So are you saying that the suction valves at the bottom of the float chamber had a glass ball beneath the screw in part, or was it a valve assembly? Still pondering this whole thing. Porsche dealer in Beverly Hills says they can order the suction valves for $79 each, but are only 200 left in Germany. Was hoping for a more local solution.

[rapidag]

Also, the discharge squirters seem to have balls in them and work. And yes, I have the swirling effect in the bowl when I pump the diaphragms. I was contemplating putting a spring and BB in each to see if I could make it work... Still pondering...

[1QuickS]

Suction valves are brass with glass ball captured inside, the ball being the active part of the valve, same for the squirters.

[rapidag]

Here are the suction check valves that I removed. They are marked "Solex 195" contain no glass balls, no visible sign of having any other parts inside. Could someone have replaced the check valves with some sort of jets?

Still at a loss on how to repair...

[James Brown]

just put the jets back in the bowl and don't mess with them, clean them first.

[ddubois]

There is a small T-shaped plug that drops into the carb body underneath each injector nozzle that I believe acts as the check valve. When cleaning the carb body they fall out and perhaps you missed reinstalling them. I don't recall the glass balls some are talking about.
The part I'm talking about is #22 on this diagram. MM is finally good for something by having this diagram on their website.

[rapidag]

I do know about the T-shaped plug that drops into the carb body. Item 21 and 22 are in good condition. These two provide the discharge valving from the accel pump. However, the suction side of every pump needs a check valve as well which in your drawing is item 16 and those shown in my last pic I posted.

I am just trying to find out what #16 looks like in good condition. I think I have a source other than Germany for them, but they are pricey and don't want to order without knowing they will work.

Thanks for all the help!!!

[1QuickS]

Hate to say this but those are air correction jets that install above the emulsion tubes. The picture below shows the check valve you need to the left of an air correction jet.

I just got it!!!!! Somone swapped the check valves for the air correction jets as they are similar and share the same thread! In fact I think I can see a check valve screwed into the tube for the emulsion tubes.

[rapidag]

So I might have my check valves screwed in above the emulsion tubes??? That would be an easy fix. I will look first thing when I get home tonight.

Thanks!!!!!

[rapidag]

Mystery solved!!!! I went home at lunch, pulled the air correction jets out of the accel pump suctions, removed the inlet check valves from the top of the emulsion tubes, placed in their proper location and... works perfect.

I installed the discharge tubes, filled the bowls half way with gas, then stroked the accel pump actuation arm... all three discharged smoothly and perfectly... just like they might have been designed to do.

Root cause: Operator error. Stupid mistake that has taken me far too much time to correct. Thank you all very much for your input and really big thanks to 1QuickS for spotting the problem.

Now I need to pull the other carb and make sure I didn't make the same mistake twice (I think I may have...)

Thanks again!!!

Mike

[69BahamaYellow]

When you install the gasket between the upper and lower halfs of the carbs, double check the gasket to make sure all the vent holes are clear. When the gaskets are made, sometimes material is left in place, where a vent hole should be, and if these holes are plugged, the car will run fine, but suck all kinds of gas into the motor, after you shut if off for a while. I won't bother explaining how long it took me to find that problem, but I sure don't want somebody else to go through the trouble, so double, tripple, quadrouple check your gaskets if you have to

[rapidag]

Other carb was assembled correctly. I guess I had a 50/50 chance of getting it right. Car runs, but not well... took my first shot at adjusting the carbs, not great, but I am not giving up yet.

And yes, gaskets look to be lined up properly. I did have to cut out a bit of material from the gasket that goes between the top body and the velocity stacks. It was overlapping in to the flow area and I didn't want reduced air flow.

[James Brown]

Don't be afraid to try bigger jets to get it to run right. Now that there running , time to experiment! Nice to have a dyno in your garage for this part.

[rapidag]

Update! Carbs are in, car is running. It's a bit rough after my first shot at adjustments. Does anyone know where to get the measurement vial for the accelerator pumps?????

Thanks,

Mike

[James Brown]

Easy, Paul Abbott

[1QuickS]

Not so easy, I don't have them. You could try PMO as they supply plastic ones with their carb kits. Best and easiest would be to go to a pharmaceutical supply and get a small syringe.

[James Brown]

I think the plastic ones are fine and cheaper.