Motorcycle Repair: Honda CT90 1969 K1b (Carb issue), honda ct90, altitude compensation

Question
I recently bought a 1969 K1b CT90.  It was a barn find, has 296 original miles on it (wow).  Needless to say carb was gummed up.  I've cleaned it, replaced gaskets and all of the other necessary restore duties to get it running for the first time.  This carb is the only year that it had the rubber float bowl gasket seating in the groove (may help Identify exact model).  As of now, I can start it first kick everytime. It will only start choke off.  It will initially run for 30 secs or so, that is while I'm giving it throttle to keep it from dieing, without throttle it dies.  It will not idle. I can restart it over and over, but only with giving it gas while kicking it over where it fires and dies in a second.  Air screw is 1 and 1/4 turns, Compression is full, is not flooding.  To me and other non-experts it seems its starving for fuel.  here's the kicker....If I let it sit for 30 minutes or so, I can start it and it will run for an extended period of time again (30 secs).  I'm at a loss. I've replaced all orings, blown out jets, so on so forth.  Any ideas or direction would help.  One more hint.  If when its running I try to choke it, it dies instantly, with choke I get no fire. Thank you for your time.

Answer
Cody, I checked the illustrations at

http://www.cmsnl.com/honda-ct90-trail-90-k1-us_model620/partslist/E++13.html

to see what it has in this model. Looks like that one has the high altitude compensation system, with #35 idle jet and #75 main jet. Float level should be 23.5mm with the needle just closing but not compressing the spring loaded tip.

#4 on the list should have been removed and checked for plugged cross-drilled holes, as well as the air bleed passages in the carburetor throat. If there is no air in those ports, the fuel will be drawn up unmixed and will flood the cylinder with mostly raw fuel.

Other things that effect idling and running at idle are valve clearances... .002" cold on intake and exhaust. Spark timing must be accurately set at the F mark (points just opening).

Try running it with the altitude compensator knob out to see if that makes it better. If so, then the carb is getting too much fuel from either idle circuits, high float level, emulsion tube holes plugged or inaccurate ignition timing.

Bill Silver