Zenith questions

jhjacobs

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I have a bunch of Zeniths completely disassembled on the kitchen table and interestingly I am finding subtle differences between them. I am curious about a couple of thing and wondering if anyone here has any insights:

1. One three of the carbs I found metering rods in the primary venturi feeds (in addition to the jets). Two of the metering rods have a small flanged input at the bottom and one is large and not flanged. Surprisingly, the carbs I have collected are in pairs and the metering rods were on one unit in from a pair and not the other. This makes absolutely no sense to me. I am going to install the smaller metering rods in both final my assemblies knowing that I can take them out. Additionally, two of the carbs have the hole where are metering rod would go blocked off with a plug on the secondaries and the rest don't.

2. One of the carb pairs I have came from a 2500S. On this pair there was a rectangular assembly on the side with a 20 ohm resistor wrapped in a brass heat spreader. This assembly is not gas tight and appears to be connected with an air feed directed into the secondary venturi. This resistor will get pretty warm with time but I can't figure out what purpose it serves. The best I can figure is that it is supposed to warm a slow air feed that mixes with the fuel stream on the seondary venturi or perhaps it is an anti-siphon mechanism? They're mounted on the outer top of the carbs and I don't plan to use them but I am curious.

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jhjacobs

Member
Messages
910
Reaction score
6
Location
Oak Ridge, TN
I have a bunch of Zeniths completely disassembled on the kitchen table and interestingly I am finding subtle differences between them. I am curious about a couple of thing and wondering if anyone here has any insights:

1. One three of the carbs I found metering rods in the primary venturi feeds (in addition to the jets). Two of the metering rods have a small flanged input at the bottom and one is large and not flanged. Surprisingly, the carbs I have collected are in pairs and the metering rods were on one unit in from a pair and not the other. This makes absolutely no sense to me. I am going to install the smaller metering rods in both final my assemblies knowing that I can take them out. Additionally, two of the carbs have the hole where are metering rod would go blocked off with a plug on the secondaries and the rest don't.

2. One of the carb pairs I have came from a 2500S. On this pair there was a rectangular assembly on the side with a 20 ohm resistor wrapped in a brass heat spreader. This assembly is not gas tight and appears to be connected with an air feed directed into the secondary venturi. This resistor will get pretty warm with time but I can't figure out what purpose it serves. The best I can figure is that it is supposed to warm a slow air feed that mixes with the fuel stream on the seondary venturi or perhaps it is an anti-siphon mechanism? They're mounted on the outer top of the carbs and I don't plan to use them but I am curious.

[/img]
 

bill

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zeniths

Can't help with the metering rod issue...perhaps a PO was messing around with different sizes?
The heated brass spring assembly is a "thermostart" valve. It enriches the mixture on cold starts.I have them on my Zeniths, which have been replaced by Webers.

Bill
'74 3.0CS, 4310008
 

bill

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555
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stockton, nj
zeniths

Can't help with the metering rod issue...perhaps a PO was messing around with different sizes?
The heated brass spring assembly is a "thermostart" valve. It enriches the mixture on cold starts.I have them on my Zeniths, which have been replaced by Webers.

Bill
'74 3.0CS, 4310008
 

jhjacobs

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Thanks. I found both documents and I have the Blue books. I decided to use Zenith X's which do not support cold start valve. I am still baffled by the metering rods. Not so much that they are used or where they install but why individual pairs I had were not matched; some and none, some had one, and some had different sizes, and no pair had them on both. I have installed the smaller size metering rods on both carbs I'm now using and they seem to work very well. I haven't done an HC / CO test to be sure but I may go and do this just to be sure.
 

jhjacobs

Member
Messages
910
Reaction score
6
Location
Oak Ridge, TN
Thanks. I found both documents and I have the Blue books. I decided to use Zenith X's which do not support cold start valve. I am still baffled by the metering rods. Not so much that they are used or where they install but why individual pairs I had were not matched; some and none, some had one, and some had different sizes, and no pair had them on both. I have installed the smaller size metering rods on both carbs I'm now using and they seem to work very well. I haven't done an HC / CO test to be sure but I may go and do this just to be sure.
 
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