Holley 1920 1 barrel tuning and adjusting
hi everyone
Im trying to find the best way to tune and adjust the Holley 1920 1 barrel carb on my 225 /6.
I completely cleaned and rebuilt the carb,but seems to be running rough.I adjusted the idle the way it says in the oldd manuals,but now it seems to run even worse.I dont want to mess with the air/fuel mixture screws (if I dont have to)And how do you get the chocke to actually work on these carbs?Mines a 72 Duster.Any ideas and advice on how you adjust your carbs for the best performance is welcome.Thanks
First, let's start with understanding under what conditions this is running rough. Is it running rough all the time, at idle and acceleration and at cruise, or just at idle? How about hot vs cold? Is the choke butterfly clsoing when closed and when cold? What is not working with the choke: is it not working at all or too much or ???? Please help out out with a bit more info. How did the carb run before the rebuild?
Next, do you think that all the hoses are on right and that the gasket at the base of the carb is installed right and sealing? This gasket has a certain orientation.
Have you checked the float level with the car running? This is the most important post-rebuild check to do as it effects almost everything in the carb operation. This is easy: with the car level, remove the 3 screws on the economizer valve (power valve) and lift the economizer out. Then start the car and measure from the flat machined surface (where the economizer valve screws down) down to the the fuel level in the bowl. That distance ought to be around 11/16".
BTW, only the idle circuit has a mixture screw to adjust; the cruise and hard throttle mixtures are fixed (unless you change the main jet, which should not be necessary). You should not hesitate to adjust the idle mixture screw in the side of the base of the carb. If the carb is OK and the float level is right and the installation is right, then you should find a good smooth running setting for this mixture screw. Adjust as follows:
- Warm up the engine fully
- Set the idlle speed screw up so that idle rpms are a bit high
- Adjust the idle mixtrue screew for smoothest operation.
- Reduce the idle and readjust the mixture screw for smoothness
And, if you have other issues, like bad spark plugs or wires, or the distributor timing off of where it should be, then adjusting the carb right is going to be nigh impossible. Do you think/know if everything else is good?
BTW, I just rebuilt a 1920 last weekend that had not been touched in 52 years and it runs perfectly. They are dirt simple carbs and reliable when they are right. (I had to re-build the accel plunger+diaphragm assy from old and new parts since I got the the wrong new assy but it works fine now.)
