Accelerator pump question

[Ron LaDow]

Modern accelerator pumps have been problematic with delivering fuel consistently....
Jim Kaufmann
356 Carburetor Rescue

And HOW!

[Ron LaDow]

It seems to be quite an effort--not to mention expense-- just to use the existing screw and avoid an incorrect choice of picking up the special one and starting it into a non matching threaded hole when repairing the carburetor.

Ab,
I was surprised at the cost; something like $80 for the first and around $100 for three. Grinding the tool took all of 15 minutes or so, and I must have repaired something close to a hundred of the things. Tooling cost was approaching the insert cost.
And while I got calls about the other screws stripping when a customer decided to just 'tighten things up a bit', none of those ever let loose.

[Larry Coreth]

Richard,

At the risk of seeming a bit forward, but the method I outlined came from Stoddard in 1983 when they were still independent AND I have used this method on my Zeniths and several other sets of over the past 30+ years. It is proven, it works, what more do you want ? !

[Jeffrey Leeds]

BelMetric, a sponsor of our TYP356NE group, offers a M6x1.0 Time-Sert Kit for this problem:

https://www.belmetric.com/ts1610-m6x10- ... 17_218_228

What am I missing? If I use the above mentioned kit and I use my M5x0.9 screw wouldn't it too loose? I'm enjoying this discussion and I am leaning toward Larry Coreth's suggestion of using the helicoil size M5 x0.8 and carefully / slowly inserting the original M5x0.9 screw.

Rich

You are not missing anything Rich. My mistake in sizing and I apologize for not doing a better job of proofreading my post. But no apology for recommending the Time-Sert instead of the helicoil. There is a large consensus that Time-Cert's are a big improvement over the helicoil. Available here in the M5x8 size from our sponsor:
https://www.belmetric.com/timesert-metr ... 8_227.html

[Olivier Auvray]

"M5 x 90 repair set" available in France....... not cheap but available!

[Jeffrey Leeds]

But of course!

You can safely say that this is the ONE item missing in everyone's tool box, for sure. And think of the Concours points you could gain if you had this in your travel kit.

I'm surprised Sebastian hasn't come across one of these during his eBay forays. (added by edit)

[Dick Weiss]

The problem of top cover gasket leakage is due to top cover warpage from tightening the screws over the years--and even 2-different gasket thicknesses--original and aftermarket.

I flat lap the top cover, body, and even the base surfaces. There are times w/the top cover being really warped and any machining would make it worse! I re-peen the cover's outside surface (w/o any markings/can't be seen) to minimize the lapping procedure.

I've never needed any heli-coils to repair the commonly stripped hole for the spring hook; there may be enough thread @ the hole's bottom for an undercut screw to hold the hook. If not, I've used a 6x1,0 bolt w/a modified head to match the other 4 since it'll fit the only location for it. Oh, the hook's hole must be slightly enlarged for it.

The banjo bolt boss being stripped (again due to stress' over the years) is repaired w/a special bronze double-threaded insert (made by me) bonded to the hole--yes, w/JB weld, and the gasket face is flattened squarely. I have exchange top covers in my archives.

Dick

[Mark Yarrish]

Along the same lines related to the Accelerator Pump functionality...

I recently rebuilt my Zenith 32 NDIX's, now working through the tuning and getting them running on the car properly. I set my floats via the Precision Matters float gage.

Now I am looking at the accelerator pump volume. When trying to measure on each of the 4 nozzles with two pumps of the throttle, I get no volume! I have tried to move my vial around to capture the fuel out of the accelerator nozzle. But No volume is captured... nothing.

Now the car does idle and drive. It accelerates fine at higher RPM, but at lower RPM's it does seem to sputter.

Questions:
1) (maybe a dumb one) but you need to measure the volume of the accelerator pump with the engine OFF, correct? Otherwise my fancy straw may get sucked in... Correct?
2) If I have no volume coming out of any 4 of the accelerator pumps... how does the car run, and accelerate?
3) Do I need to remove the carbs, and try to force air or something through the pin holes? I find it strange that all 4 are producing no volume? - Is my method off? - I have a bent straw, under the tube... car is off... floats are full (post idle), and push down on the throttle linkage 2x?


A little perplexed.

Thanks,
Mark

[David Jones]

Mark, with the carb top off and a spare accel pump to hand. Push it down the pump cylinder and see if it squirts out the relief hole in the carb float bowl and also out and over you. If it does then check the valve at the bottom of the cylinder in case it is stuck. After that remove the jets that hold the accel pump tube/jet in place and see if there is fuel at that point. If there is then remove the tubes and clear the holes in the tube. I use a needle from a hypodermic syringe which is 0.26mm diameter and is smaller than the jet hole so does not enlarge it.

[Bruce Smith]

Mark,

The accelerator pump functions to provide momentary fuel to smooth out the transition when accelerating. The engine will run w/o them and your car sounds like it's running with the symptoms of them not working. Zenith accelerator pumps are a bit finicky and, depending on the replacements that you're using, sometimes tough to get to consistently pump. You are best off troubleshooting the problem with the carbs out of the car. A few things you can try is to gently stretch the leather pump sheaths away from the springs. Also, make sure that the pump cylinder is clean. Going over the bore with 1000 grit might help as well. Before you worry about measuring the volume, make sure they are squirting. If still no luck, you may need replace the pumps. You could also try reinstalling the original ones you removed if they aren't too worn.

Cheers,
Bruce
www.cfi-auto.com

[Mark Yarrish]

Thanks for the quick replies. I will take the carbs off tonight and take a closer look.

If and when I do get those suckers pumping, to set the volume on the bench, will it work to have the carb tops off, and if needed pour a little fuel in the float bowls to give it something to suck up?

Thanks!
Mark

[Bruce Smith]

Sure, but you'll need to secure the cover and reconnect the pump link arm to actuate the pump.

[Ron LaDow]

Take a look here:

The pencil marks show the required stoke. Note also that the piston is driven by a spring, rather than any direct driver; the piston has to be 'persuaded' to accomplish its mission.
Bruce mentions stretching the leather 'skirt'. Alternatively, some are too large and stiff; they need a run against a grinding wheel to soften the periphery. Regarding sanding the bore, I used a 'bottle-brush' hone in a very small size.
But look at that photo and aim to make that part of the travel workable as a result of that spring driving that piston.

[Mervyn Hyde]

Same problem here. Have bought some nice gauges to check all the jets and new gasket kits. Flattened all the surfaces, cleaned everything and re-fitted the good condition shut off valve and accelerator pump. One the bench with a fuel line and bulb, filled the bowls until the flow stopped and checked the float level with the Pre Mat device. Float level is now spot on with the thinner spacer washer now under the shut off valve. However, no squirts from the accelerator pump nozzles. I can add that the pump was squirting through the accelerator pump nozzles before I started this checking process. If I pull the top off and use a spare accelerator pump it squirts fine. The lever the accelerator pump is set on the outer hole and adjusted to about 3" long overall. I have the straw calibrated already to check output with a couple of pumps, but nothing?

Can't see the pencil marks Ron?

I suspect that my lever arm is too long. Edit adjusted it to 2.7" or 68.8mm. Now squirts. Will need to measure that.

[Ron LaDow]

Can't see the pencil marks Ron?