Oil in the pony is new, but didnt find any filter to replace. I haven't tried it again with the air cleaner since it's a pain to get on and off. I did adjust the float yesterday it was off but that didn't fix it. Probably still potential fuel line issue. I got the line yesterday but they didn't have fittings so had to order those online.

I tied the choke handle to the frame to keep it closed and running long enough to start the big motor when I needed it of the trailer. Only did that because the choke wouldn't stay closed. Was fixed with the new carb top but this one is now also doing the same thing as the other and only properly closing sometimes (other reason I left the air cleaner off was to verify it was properly choked)

I think the main jet is messed up, that regulates fuel flow in the carb.

I thought about just replacing jets (carb kit didn't include them) but haven't been able to find the ones I need yet. They are clean and clear but wouldn't be surprised if they are enlarged from someone cleaning them by sticking stuff in there to clean them. If you know of anywhere to get the jets let me know. Carb is a zenith 10323 

I need a clarification of your terminology---when you say the choke won't stay closed---does that mean the butterfly is held closed and is limiting air flow resulting in a rich mixture??

Basically when I pull the choke lever some times it closes properly other times it stays open despite being pulled. I push it in and out a few times and it works again fine. I do not try and start it if the choke isn't closed properly, which is the main reason I have left the air cleaner off for now. My old carb top was doing that, this new one seemed to fix the issue until yesterday I saw it do the same thing.

yes the d4 wouldnt run without some choke. if you left the controls where the were when it last run it was happy if you touched them it wasnt. then it shattered the magneto gear and that was the end of that. try it with half choke and see what happens. and a oil change wont hurt maybe use sae 50 instead of sae 30 that might help too. does the oil level change while its sitting. check it today and then leave it sit for a couple of days and check it again. if it loose oil while sitting still it means you have a leaking gasket or main seal.

part of the problem is your choke linkages. and play in them. might be wrth while putting a light spring on the choke linkage so it keeps the choke arm in constant contact with the choke rod that would make it work every time. the throttle has to move with the governor so it is spring controlled anyway.

it would almost be worth putting a amal carberettor on it or a small SU carb you can still get parts for them most classic British bikes had amal carbs and a lot of cars had su carbs fitted.
once set up a su is brilliant the only carb known to give perfect mixture idle to flat chat(if set correctly)

Oil doesn't leak when sitting has stayed at the same level since the last time the big engine was ran, so should just be the oil cooler leak but I'll keep checking it.

I'd consider switching carbs but I'm not sure about adapting one to the pony, don't want to cause myself even more issues than I already have had. My best option is probably just to fix what I have, I'm sure it's something simple at this point I'm just messing up. If I can get it figured out soon I'll just send the carb in to be professionally redone or buy the refurbished one on ebay, just want to rule out other issues before spending that money and finding out it wasn't the carb.

Carb will run motor even if it is half worn out. Some times if the jet passages are plugged up you have to run with choke half on. If your choke butterfly is in wrong , you won’t get smooth operation of the choke. Get carb to someone that understands carbs and their operation.

Contact Roberts Carburetor Repair 712-262-5311