Fine tuning a 420

[Paul Buhler]

I've been using my 420 with good sized loads a lot lately. It starts easily and runs strong and smoothly under load. The governor works as it should.
My question is why might it run a bit rough at idle? It huffs, farts and chugs at low rpm. As soon as it starts to move, it smooths right out and gets the job done well.
I cleaned the fuel bowl today, the air cleaner has new oil, and the load jet seems to be in a good position. The idle jet is screwed all the way in - it's been that way since I rebuilt the carburetor last year. The points have been cleaned and set recently. I haven't checked the timing in a while. I haven't had a chance to run the dozer since the maintenance, but I thought I'd ask for any thoughts? Thanks. Paul

[DukeofDeere]

What happens if you turn the throttle stop screw in just a little?
Or open the idle jet 1 full turn.

Duke

[shinnery]

That is by no means an even fire engine, just look at the distributor cap, it fires both cylinders and then waits a long time to fire them again. Sorta like a Harley!! If you idle it down too far it is NOT going to be smooth. Not saying that is your problem but it could be part of it. Just a thought.
Bryce

[gregjo1948]

Have you checked the compression? gregjo1948

[Paul Buhler]

Thanks. Time to try all your suggestions. Bryce, thanks for your thoughts too; I hadn't considered the one-two, skip a beat setup. I believe that the compression's good, and close between the cylinders from past checks, but like I said, the crawlers been working hard (but not abused) and some things are bound to need re-adjusting or tweaking at the very least. I'll get back with more info soon.

[gregjo1948]

Have you determined if it's miss fireing on one or both cylinders? Could it just be plugs? Better get it fixed soon for your snow plowing. gregjo1948