You ask about the carb adjusting screws, the small one on top is the idle mix screw, the lower one is the main.
Before adjusting, make sure the air cleaner is clean (not just the oil cup, but the upper portion also). Be sure there are no vacuum leaks, the fuel is clean and good fuel supply to the carb.
To adjust the idle, get the engine up to operating temp, mag in retard position. Note the position of the screw slot, make small adjustments, remember which way you turned it so you can go back to where you started.
I believe on the Zeniths, turning the idle mix screw IN makes it richer, OUT makes it lean. So, back the screw slightly out until it runs worse, then back in to best idle, then about 1/8 turn more. Just play with it until it idles best, then slightly richer.
On the main adjustment, turning it IN leans the mix, OUT for richer. This is best set under load, which is near impossible to do. The next best is to set it by observing the throttle response.
With the engine running at full governed speed, mag advanced, manually pull the throttle linkage to idle. Release the link and the governor will full throttle back up to speed. While it is coming up to speed, listen to the engine, watch the exhaust. Again, note the position of the mixture screw. Turn it in 1/2 turn, try the throttle response. Keep turning in until the engine stumbles on acceleration. Then start backing the screw out, testing at each adjustment. When it is right, the engine will come up to speed without hesitation. A puff of black smoke is a good indication it is right.
Don't be afraid to play with the adjustments, each carb and engine is different, you will know when it's right. The carb needs to be in good working order to properly adjust. If it's flooding, or has clogged passages, or if the idle screw makes no difference, it will need to be repaired first. If this tractor ever gets worked, a plug check will tell if it's right. They should be clean, not black. If black, it's too rich. Any change to the exhaust will change he mixture. If you put the muffler on you'll need to readjust the main.
Upload one or more videos to your post. Photo filesizes should be less than 300K and Videos, less than 2MB. Formats allowed are gif, jpg, png, ogg, mp4, mov, and avi. Be sure to use filenames without spaces or special characters, and filetypes of 3 digits lower case.
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 8N and the Fox - by Zane Sherman. Dec. 13 1998, Renfroe, Alabama. Last niht I dreamed about the day that I plowed the field of about 10 acres over on what Jimmy and Dandy called the Ledbetter field. I was driving the 1948 8N Ford tractor that Jimmy bought in 48 new This was prebably in about 1951 and maybe even befor the house was built. This would have made me to be about16 years old and I drove the tractor for nothing and would have paid to drive it if I had had any money which I didn't, but neit
... [Read Article]
Latest Ad:
Sell 1958 Hi-Altitude Massey Fergerson tractor, original condition. three point hitch pto engine, Runs well, photos available upon request
[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.
