The FIRST thing you do is determine if the choke is working properly, including proper adjustment of the choke pulloff(s).My '66 Toro has a heat riser valve on the left exhaust manifold. While I don't know for sure, I'd expect that all '66--78 Toros use the same heat riser position and perhaps the same manifold. The valve is gravity operated, there is a counterweight on the valve that is lifted by a bimetal spring. When the manifold/heat riser valve gets hot, the spring relaxes and the valve opens.
Mopar, GM, and Ford (probably AMC also) all offered aerosol heat riser penetrant lube. It has a characteristic smell--very pungent. The last time I bought some, it was in an AC Delco-branded can. Different label, same smell. I think it was this stuff:
Part X88A
12302866
Super Penetrant (12 oz.)
* Penetrates rusted, corroded metal-to-metal seizures
* Lubricates for easier disassembly and reassembly
* Is excellent for freeing and maintaining the efficient operation of heat riser valves
* Effectively removes most lead, lead oxide and rust deposits
* Safe, nonflammable, fast-acting foamy spray clings to parts to penetrate and work
There is an exhaust passage that crosses the intake manifold from side-to-side under the carburetor plenum; it's fairly common for that to plug with carbon. Remove the manifold and chisel the carbon out. Even without a heat riser valve, this passage will provide
some heat to the manifold to assist in vaporizing the fuel. If the heat riser valve works properly, you won't be able to keep paint on the exhaust crossover section of the intake manifold. It will be SCREAMING hot and even high-temperature engine paint will burn off.
Just for giggles...WHY did you disable the heated air intake section of your air cleaner?