In Reply to: Re: 8N popping/sputtering at idle posted by Ed Gooding (VA) on June 04, 2026 at 07:04:12:
I adjusted my Duralast spark tester to 5/16” which set it for the conventional automotive ignition (20,000 volts). The tractor easily started on 3 cylinders and all 4 cylinders were tested producing a white spark. I did not appreciate a blue and/or yellow hue.
I also rechecked the carburetor adjustments. The idle needle yields a maximum RPM at 1/8 turn open and the main needle at 1 turn open.
The carburetor is a Marvel-Schebler that was rebuilt by a person who does only tractor carburetors. Every orifice was cleaned, new seals, gaskets, screws, float valve, bronze throttle bushings installed and precision sized to prevent air leaks. He then put it on a running engine for fine tuning.
I feathered the choke again and as I pulled the choke out about ½ way, the RPM dropped. As I slowly pushed the choke in the RPM increased, but I still cannot get rid of the roughness (sputtering/popping).
Sorry for imposing upon your time, but your comments and guidance are greatly appreciated.