I just got a pair of 78 Motobecanes running in Michigan. The carb does not use a needle, it seems to function like the old auto carburetors where the air flow controlls the mixture. I find it a little strage but it seems to work.
If you have a good spark, try this.
Remove the plug, with the gas turned off, spin the engine a bunch of times to clear it of residual gas/oil.
If the plug is not completely dry, wash it with carb cleaner or similar, then dry it well. Warming it in the oven is not all bad. Put the plug back in, turn the gas on, choke it and try to start.
If it does not at least fire a time or two on the first few spins, it will allready be flooded so turn the gas off.
If you have a good spark at the right time, the motor will fire on a little gas thrown in the intake. So if you can not at least get this to happen, you need to check the timing, fatness of the spark, and worry about compression.
Let us know how it goes,