Before adjusting the carb, be sure everything else is properly serviced, like the air cleaner, ignition system, cooling system and thermostat (if equipped), valves adjusted, fuel fresh and clean, filter screen clean and in place, oil fresh and free of fuel.
The rest of the engine needs to be up to par, good even compression, no vacuum leaks, exhaust leaks, or cracked/burned out manifolds.
Last, the carb itself needs to be in good working order. No clogged passages, no flooding, or excessively worn throttle shaft.
With the engine up to operating temperature, choke fully open, set the idle speed first. It is important that the idle is slow enough for the carb to be operating only on the idle circuit, down around 400 RPM.
Next adjust the idle mixture screw, the small top screw. The screw adjusts air, not fuel, so turning the screw in enrichens the mix, backing it out leans it. Turn it out slightly, listen for the engine to stumble, then take it in to best idle, then slightly more rich.
If it makes no difference, either the RPM is too high, the float is too high, or the idle circuit/air bleed is clogged. If so, the carb will need to come apart and be cleaned and inspected.
Next adjust the high speed screw, the larger one down below. Turning the screw in leans the mixture, backing it out enrichens it. This adjustment is more difficult as the engine needs to be under load and running on the main fuel circuit to adjust properly.
To get it in the ballpark, try this. Turn the screw in about a turn, or about 2 turns off seat. With the engine at idle, open the throttle as quickly as possible then return to idle, listen to the response. If the engine stumbles on quick throttle, back the screw out 1/4 turn. Keep repeating the test, adjusting the screw out until the engine will take quick throttle without hesitation. A single puff of black smoke is the goal.
This should get the carb into real close adjustment. You can play with it once it has been out working a while. Different loads and weather conditions have some effect on the mixture needs, so adjust as necessary.
Upload one or more videos to your post. Photo and video filesizes should be less than 5MB. 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 - When Push Comes to Shove - by Dave Patterson. When I was a “kid” (still am to a deree) about two I guess, my parents couldn’t find me one day. They were horrified (we lived by the railroad), my mother thought the worst: "He’s been run over by a train, he’s gone forever!" Where did they find me? Perched up on the seat of the tractor. I’d probably plowed about 3000 acres (in my head anyway) by the time they found me. This is where my love for tractors started and has only gotten worse in my tender 50 yrs on this “green planet”. I’m par
... [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.
