Idle (as in- as slow as it will run with the throttle lever pushed forward) is affected by the idle mixture screw. Any increase in engine speed above maybe 750rpm will be un-affected by the idle mixture screw. The carb runs on the main jet passages and nozzles when in mid rpm ranges. That mixture is adjustable with the load screw (bottom front). A perfect mixture of fuel and air is between 14 and 15 to one ratio. The best a carburetor can do is to attempt to make that happen based on temperature, external air pressure (varies with altitude) and applied vacuum at the discharge ports in the carb. The highest vacuum above the throttle plate is applied at low speed idle. (the throttle plate is closed to its stop, and restricting the air flow. This restricted flow is so small that the main jet has no flow of air past it and no vacuume is applied to the main nozzle. (all the vacuum is on top of the throttle plate, pulling fuel through the idle circuit.) At higher speeds the air flow past the venturi (where the main nozzle is located) causes vacuume there pulling proportioned fuel into the airstream. At full throttle and full load, the throttle plate is wide open, and the fule is pulled from the main jet, and load screw, and discharged out the high speed nozzles in the venturi. Your updraft carb is similar to the ones shown below, but upside down.(makes no difference) yours will not have an accellerator pump, nor a hot idle compensator, nor a power circuit. it is more basic. Your idle richness adjustment bleeds in more air as it is screwed out, and less fuel. Many adjust the opposite way more fuel out and less fuel in. I hope this helps. Jim
We sell tractor parts! We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today. [ About Us ]
Today's Featured Article - The Fordson F Ignition System - by Anthony West. A fellow restorer contacted me earlier this year asking for some help and advice on a model F that he was restoring. He had over a period of months spent a fair amount of his hard earned cash on replacement parts for the old "trembler" ignition. Sadly though all his efforts seemed to be a waste of time and money as he still couldn''t get the temperamental old thing to run correctly!! If i said that this was a little frustrating for him that would be "conservative" in fact the problem had reduce
... [Read Article]
Latest Ad:
1964 I-H 140 tractor with cultivators and sidedresser. Starts and runs good. Asking 2650. CALL RON AT 502-319-1952
[More Ads]
All Rights Reserved. Reproduction of any part of this website, including design and content, without written permission is strictly prohibited. Trade Marks and Trade Names contained and used in this Website are those of others, and are used in this Website in a descriptive sense to refer to the products of others. Use of this Web site constitutes acceptance of our User Agreement and Privacy Policy
TRADEMARK DISCLAIMER: Tradenames and Trademarks referred to within Yesterday's Tractor Co. products and within the Yesterday's Tractor Co. websites are the property of their respective trademark holders. None of these trademark holders are affiliated with Yesterday's Tractor Co., our products, or our website nor are we sponsored by them. John Deere and its logos are the registered trademarks of the John Deere Corporation. Agco, Agco Allis, White, Massey Ferguson and their logos are the registered trademarks of AGCO Corporation. Case, Case-IH, Farmall, International Harvester, New Holland and their logos are registered trademarks of CNH Global N.V.
