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GrahamPaige29

Advice on Zenith Carb

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Hi guys.  I mentioned this before but felt it was worth a new topic.  My carb on my '29 Graham is a Zenith model 11722A.  I did a rebuild on it with a kit from Carburetor Doctor.  Trouble is, one of the parts seems to be missing/damaged that wasn't included in the kit.  This type of carb has an accelerator pump which you can see in the first picture.  I'm not super clear on how this works.  But I know I had a heck of a time pulling the old one out due to corrosion.  At the bottom of the cylinder I believe there is supposed to be a valve which the piston pushes on to let in additional fuel.  Look at the bottom of the cylinder hole in the last picture.  This seems to be completely mangled because I had to effectively drill out the bottom part of the old piston.   This part is NOT included in any rebuild kit I can find online.  Anybody have any expertise on this?

 

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You probably will not find a kit with this valve included.

 

There are 24 different physical types of this valve. There are from 8 to maybe 30 different calibrations for each physical type, making for a huge investment if one wanted to put the valve in the kits.

 

When the carb was produced (about 70 years ago) Zenith DID offer (at least the literature shows they did) a major kit containing the valve. While only working on carbs since 1959, I have yet to see one of the master kits for this particular carburetor. Kit number WAS K-11722. These were offered until the ORIGINAL run was sold out.

 

You will have better luck searching old Zenith rebuilders for a new old stock individual part. OR find a machine shop willing to make a single valve. And yes, I do have them; but having made them in the past, I know how much time is involved, so the valves are not inexpensive.

 

While like closing the barn door after the horse ran away, the use of an ultrasonic cleaner BEFORE disassembly of the carburetor was started would have prevented your current dilemma. You also should check the lower piston of the accelerator pump for being out-of-round.

 

The pump works via vacuum. There is a vacuum passage in the upper casting that, when the engine is running, pulls the upper piston into a vacuum cylinder, charging the internal pump spring. When the throttle is moved to wide-open (or maybe somewhat less) vacuum approaches zero and the charged spring discharges, driving the lower piston (accelerator pump) downward discharging a small amount of fuel into the throttle area (the pump shot). When the pump piston is in the bottom position, it presses on the valve plunger, opening the valve, which adds mixture enrichment to the main metering jet necessary for wide-open-throttle operation.

 

And (opinion) the Zenith type 63 (your carburetor) is one of the finest updraft carburetors ever made.

 

Jon.

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1 minute ago, carbking said:

You probably will not find a kit with this valve included.

 

There are 24 different physical types of this valve. There are from 8 to maybe 30 different calibrations for each physical type, making for a huge investment if one wanted to put the valve in the kits.

 

When the carb was produced (about 70 years ago) Zenith DID offer (at least the literature shows they did) a major kit containing the valve. While only working on carbs since 1959, I have yet to see one of the master kits for this particular carburetor. Kit number WAS K-11722. These were offered until the ORIGINAL run was sold out.

 

You will have better luck searching old Zenith rebuilders for a new old stock individual part. OR find a machine shop willing to make a single valve. And yes, I do have them; but having made them in the past, I know how much time is involved, so the valves are not inexpensive.

 

While like closing the barn door after the horse ran away, the use of an ultrasonic cleaner BEFORE disassembly of the carburetor was started would have prevented your current dilemma. You also should check the lower piston of the accelerator pump for being out-of-round.

 

The pump works via vacuum. There is a vacuum passage in the upper casting that, when the engine is running, pulls the upper piston into a vacuum cylinder, charging the internal pump spring. When the throttle is moved to wide-open (or maybe somewhat less) vacuum approaches zero and the charged spring discharges, driving the lower piston (accelerator pump) downward discharging a small amount of fuel into the throttle area (the pump shot). When the pump piston is in the bottom position, it presses on the valve plunger, opening the valve, which adds mixture enrichment to the main metering jet necessary for wide-open-throttle operation.

 

And (opinion) the Zenith type 63 (your carburetor) is one of the finest updraft carburetors ever made.

 

Jon.

 

Hi Jon.  I did find these NOS parts online.  Would one of these fit???

 

http://www.russellsnewoldparts.com/carb-parts.html

 

Parts numbers

 

C97-15-12 POWER JET VALVE

C97-10-19 POWER JET VALVE

C97-10-24 POWER JET VALVE

 

He wants over fifty bucks for them.  Think it's worth it?  Thanks!

 

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On 2017-11-16 at 6:52 PM, carbking said:

The vendor should be able to look up the correct valve for your carburetor.

 

Jon.

 

Weirdly, this vendor does not seem to have a contact. Just payment for parts. Would anybody out there be able to look up a part number?  

 

A power jet jet valve for a Zenith model 11722A

 

 

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Hey guys I was able too find this s missing part and order one. It's the "power he valve" as is pretty hard to find. I managed to locate one after looking up the part number at the Old Car Manual Project. Great site for part numbers!

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On 11/16/2017 at 6:52 PM, carbking said:

The vendor should be able to look up the correct valve for your carburetor.

 

Jon.

Hi Jon.  I ordered a new power jet valve from Russell New Old Parts.  It seemed that the number was correct because I used a Zenith specification bulletin I found online.  Here it is...

 

But the valve didn't fit.  It was too small on it's threads.  Very frustrating.  I tried to start the car without it installed and it really flooded the engine.  There was gas pouring out of the manifold.  Yikes.  Am I correct in assuming that the vacuum pulled gas right out of that pump chamber?

 

If I were to thread a simple plug in the valve's place would it allow the carb to work?  Sorry but I'm getting really frustrated with this and thinking of ditching this carb altogether.

 

 

11277a.jpg

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