Zenith Carb Question(s)

[Wes Bender]

Everybody 's correct. It just depends on the amount of time you want to spend tuning. I like Zeniths because they're more tolerant of changes in altitude. Racers and power users like Webers because they can be tuned very accurately to a specific locale and make good power. My 1720 C engine with Zeniths runs quite nicely between 3000 and 9000 feet using 125 or 120 mains.

[Ken Tuvman]

Received my Rebuild kit and new top yesterday from 356 Carb Rescue - very clever instruction sheet showing parts in kit in Red making it super easy to know what goes where!

Carb Rescue Zenith Parts in Red.pdf

(278.2 KiB) Downloaded 101 times

[Doug McDonnell]

Franny has a decent video on tuning Zeniths: https://www.youtube.com/watch?v=Kkzn0eevoLY&t=51s

[Don Gale]

I'm not sure I understand the fuss/mystique/reverence of rebuilding Zeniths or Solex's. As a machinist and home mechanic with an advanced intermediate skill level, I routinely cleaned my carbs about once a year or 10k miles. At least 3 or 4 times with the Zeniths in my 356A and 6 or 8 times combined with the Solex's in my '66 912, my brother's '68 912, & brother-in-law's ''69 912, and the '68 912 in my Speedster. Not always necessary but rewarded with more power and smoother idle and acceleration afterwards, kind of a perk or shot in the arm. No big deal to dial them back in, never had any problems. I was always careful to note which jet went where, and to put them back in the same place & tighten them snug but not too tight and to be sure not to kick up a burr in the jet screwdriver slots. The most important step is after soaking in parts dip and rinsing off in hot water, to blow them out immediately and thoroughly with compressed air so they don't oxidize, especially all the internal passages. Don't remove the shafts or butterflies unless absolutely necessary. Whether or not to remove the venturis for cleaning is a crap shoot, maybe good to remove them periodically lest they oxidize and stay stuck. Make sure there isn't a wear detent in the float tang that rubs on the check valve and be sure the check valve needle tip seals completely and moves freely. Set the float level, measure the accelerator spray volume, ballpark the idle needle valves, sync the linkage, tweak the idle needle jets, and call it good. Best thing I ever did for the Zeniths was to block all the mating surfaces flat with 400 grit on a precision granite surface table, and repair a few stripped threads. I also took the slop out of the link rods by stretching a weak spring end-to-end between the top & bottom lever ball ends, guaranteeing more precise right/left action and syncronization.

[John Clarke]

Yes Craig
Or just be done with it Ken and fit a nice pair of Dellorto 40 DRLA's
Fit and forget!
Where is my flack jacket?
Regards Jay

[Craig Richter]

Someday I'm going to meet up with you John, and get a Dellorto lesson. Dellorto must have done something right to have such passionate fans, even if there are only two of you...

[Ken Tuvman]

Read Don's comments above - so, how critical are the float levels on these carbs?. A friend on this forum is loaning me the float level gauge that Ron sells and plan to use it but prefer to adjust floats on the bench rather than once on the engine if that is do-able.

Thanks so much everyone.

[Norm Miller]

Someday I'm going to meet up with you John, and get a Dellorto lesson. Dellorto must have done something right to have such passionate fans, even if there are only two of you...

It was a sad day when Dellorto ceased and we must tolerate Webers as the sensible option.

Norm

[Brian R Adams]

In answer (belatedly) to OP's original question about washer #73 in the Zenith diagram:

If you have the ubiquitous Walker rebuild kit, seek out the tiniest aluminum washer in there. It fits around the jet cover bolt, and into the shallow recess in the jet cover around the bolt hole, perfectly. Last week I helped a friend rebuild his Zeniths, and that tiny washer seals the jet cover very nicely. And I cannot think of any other place on the carb where it could be used.

Do not overtighten the jet cover bolt, just enough to squish the new rubber 'O' ring. If you undertighten, the worst that happens is a bit of gas seeps out, either from the cover perimeter or the bolt hole. Once the engine is running, feel for seepage, and tighten the cover bolt a bit at a time, just until the seepage stops.

Brian

[Brian R Adams]

Read Don's comments above - so, how critical are the float levels on these carbs?. A friend on this forum is loaning me the float level gauge that Ron sells and plan to use it but prefer to adjust floats on the bench rather than once on the engine if that is do-able.

Thanks so much everyone.

It's quite doable, in fact I cannot think how or why you would attempt to adjust the floats with engine on the car! You can let the engine's fuel pump fill the bowl, and check Ron's gauge to note the fuel level, but then you want to carefully (without tilting it overmuch) move the carb back to the bench to actually tackle adjustment if required.

Or, you can use a setup like this to actually fill the float bowl on the bench:

20190823_141501.jpg (2.25 MiB) Viewed 1579 times

Nearly everything available from local or online sources, based around 5/16" ID vinyl tubing available at any hardware store. The hand bulb I got at West Marine. I bought the cheap fuel pressure gauge and a 'T' fitting off Ebay. The hard item is the short section of fuel line w/ banjo fitting.

Details available.

The gauge is just to get the feel for ~3 psi. If you death grip the squeeze bulb you can force extra gas past the inlet valve! When the floats close the valve, you'll feel the bulb stiffen up, so stop squeezing it when the gauge rises quickly to 3 psi. It only takes thumb and forefinger to create that pressure.

Note: Handle gasoline only outdoors, and away from any ignition sources!

Brian

[Brian R Adams]

I corrected previous post - tubing ID is 5/16".

[Ken Tuvman]

Thanks!

I need to order 2 choke cover screws from Stoddard- fastenal
Can get them but their moq is 100 units.

I’m also told a star washer goes under the choke cover screws -
Will see if I can track those down locally.

[Brian R Adams]

Thanks!

I need to order 2 choke cover screws from Stoddard- fastenal
Can get them but their moq is 100 units.

I’m also told a star washer goes under the choke cover screws -
Will see if I can track those down locally.

All the choke covers I've seen have the star washers, yes. On my own Zentihs I applied some brush-on tar-like Permatex sealer on both sides of the paper gasket. Many years later in going through the carbs again, I never removed those choke covers, but happily I didn't need to soak the carb body.

[Ken Tuvman]

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?

[Don Gale]

yes, best to soak them vs. assembling dry. gas, wd40, light oil, ATF, etc. and wipe off the excess. they will be totally saturateda with gas soon enough. i just refurbished an old coleman camp stove that sat for decades. the leather cup was dry as a bone. brought it back to life with mink oil and a heat gun on low.