The Ford Barn

WillC · 04-27-2019, 07:57 AM

Iv complete rebuilt the this Zenith carburetor and would like to know how many turn on the air and the fuel mix should be a good starting point for starting the engine. Thank you.

wmws · 04-27-2019, 08:03 AM

I think the idle air adjustment should be out about one and one half turns.

redmodelt · 04-27-2019, 08:26 AM

That is about where I have been setting mine^.

Dick M · 04-27-2019, 11:17 AM

The adjustment screw on the carburetor is the idle/air mixture. It is set at 1 1/2 turns open as indicated above. The Gas Adjustment Valve is set with the choke rod in the cab. I always run mine at 1/4 open.

Werner · 04-28-2019, 06:38 AM

Hello Will,

I rebuilt the Zenith-2 too. I mounted new needles and yets. I can not open the idle scew more than 1/4 turn. If more, the fuel gets too fat. The gas adjusting knob inside I must open 1/4 turn always.

30 Closed Cab PU · 04-28-2019, 07:46 AM

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Use Initial setting of 1 1/2 turns from seated as indicated above. Also as indicated adjustment of the idle speed and idle mixture is typically set with GAV 1/4 turn open at motor idle, with the motor warmed up.. Adjust the two screws for best low speed idle. Most find the 1 1/2 turns the good setting for their As. This can vary with the A and carb. For some reason my truck runs best a 1 2/3. Maybe the carb has a jetting issue, do not know\. Am leaving it alone since the truck is running great as is.

chap52 · 04-28-2019, 08:40 AM

Here is some info that may help. Zenith carb basics and the adjustment procedure from the Model A Instruction Manual.
I found that after establishing a desired idle with left lever fully up that fine tuning the fuel/air mixture needed to be done slowly allowing the engine to catch up to my adjustment. Take it slow and "listen" as directed in the manual.
Enjoy the adventure, Chap

http://modelabasics.com/carb%20basics%202.htm
http://motormayhem.net/wp-uploads/20...ion-Manual.pdf
Page 24

wmws · 04-29-2019, 09:09 AM

Remember the idle mixture screw on the carb regulates air not gas. Screwing it in, cuts down on air, richening the mixture.

Ed in Maine · 04-29-2019, 09:24 AM

If you haven't flow tested the Idle Jet, you really don't know where you are going to set the air Idle Adj. Screw. The published range is 44 - 48 ml/min. If your jet is at the low end, most likely your Adj. Screw will only be opened a half a turn. If you are at the upper end (48 ml/min.) you will find the screw is out 3-4 turns getting as much air as possible to mix with the higher idle gas flow. I find that purchased jets are most likely over sized and the idle circuit will perform miserably! If you are taking the time to clean and rebuild your Zenith Carb, have all the jets flow tested. Ed

04-27-2019, 07:57 AM	#1
WillC Member Join Date: Mar 2011 Posts: 50	Carburetor pre adjustment Iv complete rebuilt the this Zenith carburetor and would like to know how many turn on the air and the fuel mix should be a good starting point for starting the engine. Thank you.

04-27-2019, 08:03 AM	#2
wmws BANNED Join Date: Feb 2013 Location: Coatesville, Pa Posts: 719	Re: Carburetor pre adjustment I think the idle air adjustment should be out about one and one half turns.

04-27-2019, 08:26 AM	#3
redmodelt Senior Member Join Date: May 2010 Location: Portland OR Posts: 6,340	Re: Carburetor pre adjustment That is about where I have been setting mine^. __________________ I know the voices aren't real but damn they have some good ideas!

04-27-2019, 11:17 AM	#4
Dick M Senior Member Join Date: May 2010 Location: Ukiah, CA Posts: 477	Re: Carburetor pre adjustment The adjustment screw on the carburetor is the idle/air mixture. It is set at 1 1/2 turns open as indicated above. The Gas Adjustment Valve is set with the choke rod in the cab. I always run mine at 1/4 open.

04-28-2019, 06:38 AM	#5
Werner Senior Member Join Date: Jan 2019 Location: Germany, near Aachen Posts: 1,157	Re: Carburetor pre adjustment Hello Will, I rebuilt the Zenith-2 too. I mounted new needles and yets. I can not open the idle scew more than 1/4 turn. If more, the fuel gets too fat. The gas adjusting knob inside I must open 1/4 turn always. __________________ Beste Gruesse aus Deutschland, Werner Ford Model A, Roadster, 1928 Citroen 11 CV, 1947 Hercules W 2000, 1976; (with NSU-Wankel Rotary Engine), Canadian version

04-28-2019, 07:46 AM	#6
30 Closed Cab PU Senior Member Join Date: Aug 2018 Posts: 2,332	Re: Carburetor pre adjustment Sponsored Links (Register now to hide all advertisements) Use Initial setting of 1 1/2 turns from seated as indicated above. Also as indicated adjustment of the idle speed and idle mixture is typically set with GAV 1/4 turn open at motor idle, with the motor warmed up.. Adjust the two screws for best low speed idle. Most find the 1 1/2 turns the good setting for their As. This can vary with the A and carb. For some reason my truck runs best a 1 2/3. Maybe the carb has a jetting issue, do not know\. Am leaving it alone since the truck is running great as is.

04-28-2019, 08:40 AM	#7
chap52 Senior Member Join Date: Jun 2013 Location: Marana Arizona Posts: 1,776	Re: Carburetor pre adjustment Here is some info that may help. Zenith carb basics and the adjustment procedure from the Model A Instruction Manual. I found that after establishing a desired idle with left lever fully up that fine tuning the fuel/air mixture needed to be done slowly allowing the engine to catch up to my adjustment. Take it slow and "listen" as directed in the manual. Enjoy the adventure, Chap http://modelabasics.com/carb%20basics%202.htm http://motormayhem.net/wp-uploads/20...ion-Manual.pdf Page 24

04-29-2019, 09:09 AM	#8
wmws BANNED Join Date: Feb 2013 Location: Coatesville, Pa Posts: 719	Re: Carburetor pre adjustment Remember the idle mixture screw on the carb regulates air not gas. Screwing it in, cuts down on air, richening the mixture.

04-29-2019, 09:24 AM	#9
Ed in Maine Senior Member Join Date: May 2010 Location: Washington Cty., ME or Flagler Cty., FL Posts: 1,106	Re: Carburetor pre adjustment If you haven't flow tested the Idle Jet, you really don't know where you are going to set the air Idle Adj. Screw. The published range is 44 - 48 ml/min. If your jet is at the low end, most likely your Adj. Screw will only be opened a half a turn. If you are at the upper end (48 ml/min.) you will find the screw is out 3-4 turns getting as much air as possible to mix with the higher idle gas flow. I find that purchased jets are most likely over sized and the idle circuit will perform miserably! If you are taking the time to clean and rebuild your Zenith Carb, have all the jets flow tested. Ed