How well do they run?

Pulling the same implements as before requires half as much throttle, and it doesn't bog down at all.
Mine came from genesee.com
Another thought, did you pull the plate in the bottom of the dist? The weights in there can stick. Or get so much gunk on them that they don't collapse completely. Shoot them with some cleaner. hth..

Larry

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The 8N9510C "not Marvel Schebler" carb is particularly bad in this regard. They will not idle below 800 RPM unless you take them apart and modify them, and suffer this sort of lean stumble (and worse) until 1000 to 1100 RPM or so. Despite this, the tractor will do any work you ask of it -- it's just that irritating sound keeps bugging me.

The off-idle "poofing" between 600 and 1000 RPM may be endemic to the economizer system -- I remember the 2N of my youth doing this as well. Does it really matter, if the tractor pulls a load? I dunno.

I suspect the clone carb could be improved by drilling an additional idle transfer hole in the throttle body, about halfway between the two existing holes. This is not for the feint of heart. You will also need to experiment with the size of the idle jet. (You can get a nice smooth 400 RPM idle if you drill out the idle jet to a 1/16 drill, BTW.) I've not got around to experimenting with the transfer passage, but may one day.

Now, if the "popping" sounds more like gunshots and the tractor is struggling to keep running, then this is abnormal and probably fixable.

If this is a new "Not Marvel Schebler" clone carb, try the following tests:

Remove the main mixture screw. See how the engine runs. Cover the hole with your finger. See how the engine runs now.

If the engine smooths out when you remove the screw, but then roughens back up when you cover the hole, I suspect you are suffering from the "clone carb plastic venturi blocks the bowl vent" bug that seems to be a design "feature" of your new carb.

If the engine pulls a load OK, and seems to run fine at higher speeds with at least some load on it, this lends support to this proposition.

The term "Chinese copy" is often considered both a compliment and a perjorative. THe copied version is sometimes almost as good as the original, but a lot cheaper. No need for minimum wage, environmental laws, or those pesky workplace safety regulations.

he flip side is often times the copies come without sound knowledge of the original design theory and without reasonable post production testing.

The entity that copied the Marvel design substituted a plastic venturi for the orignal brass venturi, presumably to save money. The thicker flange at the base covers the passage from the float bowl to the choke horn. This causes the back suction economizer to work overtime, resulting in the rough operation. Removing the main mixture screw provides an alternative means of venting the float bowl.

This problem can be corrected by substituting a brass venturi, or by enlarging the bowl vent opening with a die grinder, or both.

Alternatively, send the new carb back where you bought it, buy a used Marvel Schebler carb, and overhaul it.

This particular carb (as does the original Marvel Schebler carb) uses a reverse idle system in which the idle screw adds a controlled amount of additional air. Closing the idle screw moves the idle mixture to its maximally rich position; the reverse of a "normal" car carburetor. The usual idle quality problem is that the mixture is too lean -- easily tested by using an unlit propane torch to enrichen things at the choke horn.

The idle screw appeared to be closing off this additional air, but the mixture was still too lean for a good slow idle. Yeah, I know, check for vacuum leaks. I checked everywhere -- even built a pressure check fixture for the manifold to prove there were no hidden cracks between intake and exhaust. There weren't.

I bought a numbered drill set, and kept drilling out the idle jet until I could get a satisifactory range of adjustment out of the idle screw. I had to go clear up to a 1/16th drill before closing the idle mixture screw resulted in a too rich mixture.

With all this done, I got a very nice, smooth idle at 400 RPM. As Dell says, it sounds really, really slow compared to a modern car.

I am still not satisfied with the off-idle tip-in performance from 600 to 900 RPM. I believe the idle transfer port is too high up in the throttle body and the mixture gets too lean before the additional fuel can be provided.

And I could go on about the plastic venturi and improperly drilled bowl vent passagea as it came from the Chinese factory but maybe that's left for another posting.