ZS Carb Adjustment

Hello All,

I am trying to adjust a ZS CD carb that is running rich. I have the Stromberg tool and when I insert it into the carb, the outer tube pin is in the notch, I can not turn the allen wrench portion. How hard is it supposed be to turn? I'm wary of breaking something and everything I have read did not indicate a lot of force would be needed.

Thank you in advance for replies.

They are not generally very hard to turn.
If you take the dome top off the carb and pull the piston, making certain not to damage the diaphragm, inspect to make sure the screw(recessed toward the lower side of the piston) is properly aligned with the slot that is visible from the bottom of of the piston.
The screw should be slotted brass and not threaded to the tip.
Other thoughts are that it has been tightened into position, or maybe an accumulation of junk over time has locked it into place.

Good advice from Doug and often necessary to hold the air valve (piston) firmly in one hand and turn the allen wrench with the other. But try a counterclockwise turn first in the event the clockwise direction is at it's limit.
Sometimes the star washer that retains the adjuster/needle carrier assembly in the damper well is slightly cocked, putting a bind on the adjuster. You may need to tap it square with the adjuster, using a dowel or blount pencil.
2 things to keep in mind:
There are only 2-1/2 turns counterclockwise from fully clockwise before the adjuster threads disengage the needle carrier.
And be sure to place the index tab on the diaphram back in it's home slot in the carb body when you replace the air valve/diaphram assembly.

If it has not been used in a while (like NEVER), the o-ring seal will be nearly fused to the bore. The BEST thing to do is get rebuild kits and go thru the unit(s) completely. Some we've had to soak in an ultrasonic cleaner for hours to literally MELT the o-ring... Small drifts and 6-ounce hammers were involved.

If the o-rings are brittle and stuck, it is possible (likely, even) that you will strip out the Allen hex socket in the adjuster before the seal is broken between the bore and adjuster. Care and attention need to be applied before brute force.

DrEntropy said:

If the o-rings are brittle and stuck, it is possible (likely, even) that you will strip out the Allen hex socket in the adjuster before the seal is broken between the bore and adjuster. Care and attention need to be applied before brute force.

Click to expand...

If you don't have a bath available, soaking in "carb cleaner" should loosen it eventually as well. Of course you have to replace the ring afterwards.

The O-ring wasn't included in the kits I got, but fortunately it is a standard size.

Thanks all. I took the carb apart and I think what the problem was is the set screw that holds the needle in place was screwed so tight that the needle could not move up or down.

I backed it off so now I can move the needle using the adjustment tool.

Thanks to all.

Good! Much better than having to go thru the drill of changing out a stuck seal. :thumbsup:

Sure would like to hear the details of how you got the stripped allen hex socket out and what you replaced it with and with no questions about why I asked.

You mean the mixture adjustment screw in the top of the needle carrier ?

Yes the adjustment allen head of the screw adjuster (not the screw threads) seems to be stripped or wallowed out. I really can't blame it on the previous owner. My son may have over done it not knowing there is a set screw.

I've not had that particular problem, but I solved something similar with a "EZ out" screw extractor

by driving some thin wall brass tubing over the shank and using it as a handle. Don't recall the size of tubing offhand, but it was chosen so the inside circumference was only slightly larger than the circumference of the square shank (meaning it had to deform to fit over the EZ out shank). ISTR I also used some Loctite and waited for it to set up before using the tool.

Any hobby shop should have .014" (1/64) wall brass tubing in a range of sizes. I recently found it at my local OSH as well.

Another approach that might be safer (but will most likely destroy the needle carrier & needle) would be a long drill bit, sized to fit through the hole in the bottom of the piston, with some tubing slid over it to hold it centered (and protect the inside wall of the shaft). I don't recall the hole size offhand, but MMC offers a variety of long bits
https://www.mcmaster.com/#metalworking-and-multi-purpose-drill-bits-and-rods/=9x0wrp

Although the adjuster won't pass thru the bottom of the air valve because it sits on a ledge in the damper well, the needle/needle carrier will pass thru the top along with the adjuster,
Back off the needle locking screw Moss #366-035, slide a straight section of metal tubing, such as brake line, over the needle and tap the open end of the tubing until the whole thing comes out the top of the damper well.
Then you can decide if you want to cut a screwdriver slot in the head of the adjustment screw or drill and tap it out. You'll figure out what to do once you have the whole thing sitting on your work bench.

Only way I know to do it so you can refit properly working adjuster.

Thanks. I hate to take a hammer to the air valve but if no progress can be made other wise I will follow your advise.

Well just don't start off with a full swing like you're trying to drive a nail.

One of my other hobbies is restoring antique clocks and I use a careful hammer there occasionally :hammer: