You are correct that the little column in the corner of the float bowl is what delivers fuel to the enricher circuit. The enricher jet in the float bowl is almost always the cause. It would be nice if you could swap in float bowls from a bike that starts easily. You have 2 enricher jets, one on each carb. It only takes one obstructed enricher jet to make cold starting difficult. "Pretty darn slowly" is difficult to quantify. You might try comparing one float bowl to the other to try to get a sense of what is going on.

I fixed a poor starting bike at a campout several years ago with Makers Mark and the wire from a bread tie. I emptied the float bowl and dribbled a few drops of bourbon in to the column. I then attacked the enricher jet with the bread tie wire from inside the otherwise empty float bowl. Eventually some crud emerged from the little opening and in to the bottom of the float bowl. Several repeats of the procedure yielded  a back fill from the column that was a little more than "pretty darn slowly".

I once had trouble with the little jet (or orifice) that is IN THE BOWL. The enrichment circuit draws fuel from the small independent fuel well, in the front corner of the bowl. In the bottom of that well (in the bowl) is a tiny orifice that meters fuel in from the main bowl. That orifice can get plugged and then not much enriching occurs.  Some of these orifices are removable. On my ‘78 they are not removable, but they are easy to clean and blow out  

Also, the bowl gasket itself has to seal properly around the little enrichment well. If air is able leak in, the enricher can draw air instead of fuel. 

Here's what 98% of carb owners do not understand. Here are the 3 things every carburetor owner needs to fully comprehend (e.i. learn, recognize, be aware of, take positive actions because of)...

1. Here's the difference between fuel injection (such as found in the modern family vehicle) and carbs. With FI, the fuel is under pressure to enter the engine. Clogging almost never occurs. If it does, then the fuel pressure pushes obstructions on through. In a carb, fuel is "lifted" by vacuum, and as every engineer knows, "vacuum sucks !" In a carb setup, obstructions simply get worse because the force of a vacuum is nearly zero. There is no (e.i. zero, zilch, nadda) "pressure" or "force" moving the fuel. Once coating of the jets starts (and all carbs do it), without intervention it only gets worse over time. And the "time" element is completely dependent upon the quality of the fuel the owner places into the tank. Stagnant fuels allow this coating process to proceed faster.
2. Gasoline with Ethanol is the worst thing that ever happened to carburetors. Ethanol does NOT stay in solution with gasoline. When the liquid is allowed to become stagnant, the ethanol comes out of solution with the gasoline. In the un-agitated can, tank or float bowl 2 distinct layers of liquid form: gasoline and alcohol. The alcohol layer quickly starts to attract water. Your engine cannot burn alcohol or water, and so engine performance suddenly drops, or stops altogether. Worse yet, the combination of alcohol and water can either form corrosive compounds that can physically damage the alloy of the crab AND/OR form a varnish-like coating that quickly works to close off fuel jets from fuel flow. The smaller jets are always affected to a greater extent. The smaller jets are primarily the ones used to start an engine. Thus, ethanol damage = poor starting.
3. Because of these facts, owners of carburetors need to be proactive in their maintenance. They need to enact a plan or procedure to protect themselves, and insure the correct operation of all their equipment with carburetors. This list includes: motorcycles, lawn mowers, chain saws, string trimmers, leaf blowers, in short any engine with a carburetor. Some tips...

• Do not allow ethanol fuels to sit in any engine or fuel can for longer than 6 weeks. Especially not over winter. Drain or run all the fuel out before storage. After draining, leave the fill cap off and drain plugs out, and allow the cavity to air dry.
• Especially in motorcycles, use a high-quality Top Tier fuel with a cleaning additive. Read: https://toptiergas.com/
• Especially with lawn equipment, treat the fuel with a stabilizer AND cleaner (such as StarTron). This is best done in the can as soon as the fuel is brought home. By treating the main fuel can, the treated fuel eventually works its way into all the equipment. 

Hope this helps.

PS. With the R90's Delorto, dosing each tank of fuel with a tablespoon of StarTron will greatly help, but to get the treatment thoroughly distributed throughout the entire carb body it may be necessary to momentarily open the enrichener valve while going down the road. That is, circulate fuel in those jets and passageways at times other than only during Startup. 

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@wobbly

Just to be clear, I followed your advice earlier this year and put the bike away with a bone dry tank. Pulled the float bowls and cleaned them as well. They look fine but can't see much of that enricher jet. 

It actually started well enough off of hibernation on the fresh gas - now the second tank full. 

I'm going to compare and work on those channels. 

thanks

I remember that now.

The cleaners found in some US gasoline brands, like Chevron and Shell, (especially when coupled with StarTron) will clean the places you can't get to while you ride. Of course it will take longer for that to occur, but riding is a lot more fun than disassembling carbs !

The carbs only require disassembly when the jets are completely clogged. As long as some fuel can flow through the jets and passageways, you will experience improvement. This is why I recommend opening the enricherner occasionally... just for a half-second after the bike is fully warmed and you are cruising in high gear. 

All the best.

Now you're talking. I really like making sure the enricher jet is happy by opening it up under way for a bit. I'll grab some Star Tron as well. 

Thanks a lot. 

I know I would have a little hard starting after sitting for the extended upper Midwest winters.  Set valves, checked carbs, etc.  Mine was as simple as tossing a little heat on the oil pan.  I use 20w50 in mine.  Just thinning the oil from the cold temps helped mine fire right up.  May not be the problem, but may be worth a shot if the conditions are similar.

Posted by: @jnicks01

I know I would have a little hard starting after sitting for the extended upper Midwest winters.  Set valves, checked carbs, etc.  Mine was as simple as tossing a little heat on the oil pan.  I use 20w50 in mine.  Just thinning the oil from the cold temps helped mine fire right up.  

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