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

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

#16 Post by Ron LaDow »

Brian R Adams wrote: Mon May 06, 2019 9:19 pm [...]The bore seems tapered top-to-bottom, so that complicates hone selection a bit, but only the bottom half or third of the bore takes needs to seal.
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Two points which are not well understood:
1) The piston/skirt is driven by that spring; there is no direct structural connection between the drive lever and the skirt.
2) .3cc total per stroke; the travel is something on the order of .1" (from memory; I milled a slot on an old body and measured it at one time).
You need to hone the bottom of the bore and the bead-hone will conform to the diameter; ignore the upper 95% of the bore.
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Gary Koehler
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Re: Zenith Accel. Pump Plunger Assy. Sold In Classifieds: Feedback?

#17 Post by Gary Koehler »

LaDow:
“You can get more of them to work yet if you hone the bore; there is a 'bead hone' small enough to fit in there and a light honing would up the success rate as much as grinding the edge of the skirt would.”

A bead hone generally has a long taper on the end and will not hone to the very bottom.
A better choice is to use a Scotch-Brite Rotary Bristle Disc. Shown in 2nd photo is single one in 80 grit (yellow) and a good starting grade. Mount about six of these on a mandrel and you can hone right to the bottom, use a Dremel tool.

The stuff that comes out of this bore is NASTY- you do not want to breathe it, wear a respirator. There are other grits shown in the first photo, but a stack of about six will generally give you the surface finish close to original. If the surface is really corroded use a higher grit (lower number).
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Brian R Adams
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Re: Zenith Accel. Pump Plunger Assy. Sold In Classifieds: Feedback?

#18 Post by Brian R Adams »

Ron LaDow wrote: Mon May 06, 2019 9:39 pm 2) .3cc total per stroke;
All my references specify .2cc to .3cc total for 2 strokes (for A or B engines) FWIW.
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Ron LaDow
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Re: Zenith Accel. Pump Plunger Assy. Sold In Classifieds: Feedback?

#19 Post by Ron LaDow »

Brian,
That spec is per nozzle; the pump feeds both.
Gary,
Where'd you find an arbor long enough to get to the bottom?
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Re: Zenith Accel. Pump Plunger Assy. Sold In Classifieds: Feedback?

#20 Post by Brian R Adams »

Ron LaDow wrote: Mon May 06, 2019 9:39 pm ... the travel is something on the order of .1" (from memory; I milled a slot on an old body and measured it at one time).
Fairly easy to sanity check that using rough measurements from a 6" scale:

External pump lever arm (to middle hole) is ~42/32"
Internal pump lever arm is ~28/32".

From rest (throttle closed) position, the external lever's middle hole moves about 7/32" to where the pump bottoms out (and spring starts to compress) depending on actuator rod length adjustment.

So: pump travel = (7 x 28 / 42) / 32 = 0.146".

That's certainly in the ballpark of the 0.1" you recall. The well is 1.925" deep, so 0.146" is still only the bottom 7.5%.
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Re: Zenith Accel. Pump Plunger Assy. Sold In Classifieds: Feedback?

#21 Post by Brian R Adams »

Ron LaDow wrote: Tue May 07, 2019 11:20 am Gary,
Where'd you find an arbor long enough to get to the bottom?
With the pump pressure valve removed from the bottom of the well, you could drop the arbor end down first, out the valve hole, then chuck it in the Dremel and reach the bottom of the well and up a bit from there. If the arbor is a bit longer than 1/2 the well depth, you could also touch up the upper well by entering from the top.
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Re: Zenith Accel. Pump Plunger Assy. Sold In Classifieds: Feedback?

#22 Post by Gary Koehler »

Ron,
I don’t have any 80 grit wheels mounted presently, but here are 5- 50 grit wheels on a Dremel mandrel. Calipers are set to 50 mm, The collet chuck is quite a bit smaller in diameter than the bore. Don’t fire up the Dremel outside of the bore @30,000 RPM, you’ll have a bent mandrel...
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Re: Zenith Accel. Pump Plunger Assy. Sold In Classifieds: Feedback?

#23 Post by Gary Koehler »

Re Dremel

ps. Might be a Scotch -Brite mandrel..

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

#24 Post by Brian R Adams »

gary koehler wrote: Fri May 10, 2019 10:26 pm Re Dremel

ps. Might be a Scotch -Brite mandrel..
That doesn't look like the 3M mandrel, which I just ordered w/ some discs. The 3M (Scotch) looks like the one in the 3M data sheet that comes with the discs, and lacks the stepped shaft diameter. The 3M mandrel looks to be about 35mm (1.4") long.

Here are some pics of the bottom section on my pump bore, taken using a low-grade firearm bore scope. The progression left-to-right, from the bottom of the well (and inlet hole), a ~1/4" pitted section, a transition are w/ annular grooves, then to a relatively smooth section above the travel range of the plunger skirt and backing washer. I believe the annular rings are caused by the steel backing washer, which with the OEM leather skirt worn thin, makes contact with the walls.

As you can see, I have already removed any scale from the walls, by spinning (slowly, by hand) a 20-ga shotgun bronze bore brush with solvent. What I am hoping for is to smooth out the pitted and ridged portions, enough to reduce the drag on the new leather skirt, without increasing the well's diameter enough to compromise seal. To that end I have ordered 10 80-gr bristle disks and 2 mandrels.

[Note: Magnification and source light angle greatly exaggerates the "relief" in the photos!]
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Gary Koehler
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Re: Zenith Accel. Pump Plunger Assy. Sold In Classifieds: Feedback?

#25 Post by Gary Koehler »

I have bought mandrels from three different sources: 3M, the Dremel supply at either Ace hardware or Home Depot, Or at Otto Frei – they are a supplier of quality jewelers tools and parts, and have a lot of buffing and polishing hardware items. Also my source for the radial bristle discs.

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

#26 Post by Brian R Adams »

gary koehler wrote: Sat May 11, 2019 10:18 pm I have bought mandrels from three different sources: 3M, the Dremel supply at either Ace hardware or Home Depot, Or at Otto Frei – they are a supplier of quality jewelers tools and parts, and have a lot of buffing and polishing hardware items. Also my source for the radial bristle discs.
That 50mm reach should allow access to the bottom of the pump well from topside.

Remember Bourget Bros? Longtime mail-order jewler's supply in SoCal, now defunct. They had everything, great customer support.

Here are some pics of a 20-ga shotgun bronze bore brush in use. The shaft has a T-handle (not pictured) on the drive end. Of course you must remove the pump valve from the bottom of the well to pass the pointy end of the brush and allow the bristles to reach the bottom of the well. It's a fairly tight fit, you need to twist the brush to insert it, and it takes a bit of elbow grease on the handle to twist it while fully inserted, and you shouldn't try to reverse direction, twist it clockwise or anticlockwise, but only one direction.
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Re: Zenith Accel. Pump Plunger Assy. Sold In Classifieds: Feedback?

#27 Post by Brian R Adams »

Question: Should the accelerator pump nozzles (part 79 in the Zenith exploded drawing, not the metering jets) that hang above the venturis come back out the same hole the jets go in, easily? Mine are tight and feel permanently affixed.

I have one nozzle which seems a bit clogged, it doesn't squirt straight down like the other, and it puts out less fuel than its partner.

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

#28 Post by David Jones »

I have found that the needles for my insulin pens are perfect for unclogging the acccel pump jets in Zeniths and Solex carbs. Find your local friendly diabetic and scrounge a few needles.
If I had known I would live this long I would have pushed the envelope a little harder.
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Re: Zenith Accel. Pump Plunger Assy. Sold In Classifieds: Feedback?

#29 Post by Ron LaDow »

Brian R Adams wrote: Sat Jun 01, 2019 8:53 pm Question: Should the accelerator pump nozzles (part 79 in the Zenith exploded drawing, not the metering jets) that hang above the venturis come back out the same hole the jets go in, easily? Mine are tight and feel permanently affixed.
I have one nozzle which seems a bit clogged, it doesn't squirt straight down like the other, and it puts out less fuel than its partner.
Brian
Removal of the nozzles is easy; lay the carb 'inside' on a flat surface, lay a flat-blade screw-driver on the end of the nozzle and tap with a 4-oz 'toffee hammer'.
No come out? Up the anti to a 6-, 8-, more hammer. They have been 'installed' incorrectly-clocked using the force of the jet threads. Not good news.
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Re: Zenith Accel. Pump Plunger Assy. Sold In Classifieds: Feedback?

#30 Post by Vic Skirmants »

After 56 years with these cars, I am still learning. Much of my carb experience has been in racing, using tiny accelerator pump outputs just to help getting the engine started. Don't need that extra fuel into the engine when running at high revs; it just drowns the mixture. Of course it is critical in a street-driven car to carry over from the idle jet circuit to the mains. I was having trouble with a newly-acquired 65 with Zeniths. Pumps weren't working well at all. This discussion thread taught me that my problem was with the accelerator plungers, which were not going through the full range. Dug out some old ones, and bingo! Problem solved.
Thanks, Ron and Gary, and all the others for your discussion; it helped tremendously.

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