Gy6 idles/reva fine but struggles under a load

[geep]

Engine is a 1p63qml on a kandi cart. Motor had blown from low oil (son left oil cap off) and the piston and cylinder was scarred. Replaced with a new cylinder, piston and head. Kart fired right up, but when accelerating or under load it seems to choke out/struggle to run properly. I have:

Double checked timing. Moved one link forward and one link back to double check, but it runs worse/barely starts.
Disassembled and cleaned carburetor (that which isnt riveted)
Checked vacuum lines, intake manifold, carb diaphragm and transmission casing all go to a single pcv valve.
replaced fuel filter
Spark appears robust
What else might I be missing? I used a run-of-the-mill 63mm big bore kit, new head (old head exhaust valve was letting light through) and a new valve cover as the old cover had one bolt hole out if place. Thing sounds awesome at idle (sounds much throatier than previous engine) but it doesn’t really go anywhere.
Running out if hair to pull out.

 

[Hellion]

Sounds like good ol' classic BOGGING.

If it is, It could either be a lean bog or a rich bog. At any rate, the air fuel ratio it’s looking for is not being met, either because you don’t have enough air or you don’t have enough fuel.

 

[geep]

That wouldnt be so bad as long as I can address it I suppose. Its a stock carb, should I replace with something more adjustable? Is it possibly a function of the diaphragm in the carb getting bad vacuum signals and not opening the needle valve enough? Should have more than enough air, havent gotten a filter on yet (so maybe too much air)?

 

[Hellion]

Its a stock carb, should I replace with something more adjustable?

I don't know the stock carb but I would surmise that it could be basically non-adjustable leaving you with almost no choices, but you need to sort it out or help us sort it out. Could be as simple as turning a mixture screw; and it's not something that's often "one and done" it might require a more tedious adjust-then-test X (times) as long as it takes.

Got pics?

 

[geep]

Makes good sense. When I say 'stock carb' I mean un-adjustable, I can't even get to the float without drilling out rivets. But that's ok, I get the gist of what you are saying... I'll try to gain some more flexibility (maybe an adjustable carb) so 'we' can try some things, as what I have is anti-tinker lol. I appreciate the feedback, I'll come back when I have something better to share and/or pics to go with. Thanks!

 

[Denny]

Drill the rivets out and then tap for machine screws. Running without an air filter is just making matters worse. Probably too lean due to the bigger bore.