Weird smoke coming out.

Pull the spark plugs and please for the sake of others following this thread tell us if they look like it's running rich.

If the plugs appear like it's running fine, ie. a light-tan color on all 4 plugs -- it's probably not running rich.

As to 'why does this problem not appear until 5-6 minutes' -- quick question to that would be 'what changes on the bike from startup to 6 minutes' -- HEAT is one thing.

Be careful about the plug read -- even though you're thinking it's not oil burning, the appearance of too much oil being burned vs. running rich on the spark plug's appearance needs to considered. I don't have photos of plugs but if you can find a series of photos on this site or another web site, you will quickly see that a spark plug showing overly rich looks different from a plug where 'burning oil' is a problem.

i pulled the plugs already and they were coated in carbon. cleaned them and put them back in. i'm pretty sure they've been in there for awhile. as to pictures, i will google that tomorrow and reply about what they looked like.

www.totalmotorcycle.com/maintenance/sparkplugs.htm

according to the pictures there, mine was looking like it had alot of carbon deposit on them.

"Black fluffy carbon deposits indicate an overly rich fuel mixture or possibly a weak spark. Check for such things as a stuck choke, a heavy or misadjusted carburetor float, a leaky needle valve in the carburetor, leaky injectors, low coil output or high resistance in the plug wires."

i took that quote from another site talking about a 'fuel fouled spark plug'. it seems that i'll only be able to figure this out when i'm able to get the bike out early next year.

All good thoughts, over flowing carbs are common , contaminating crankcase and venting fuel/oil vapor to airbox, resulting in fuel/oil in exhaust and smoking issues as exhaust comes to temp. I'd check petcock for complete shut-off. change oil, and allow for an extended warm up cycle. (residuals in exhaust often require prolonged periods to burn off) luck G

Am thinking these carbs have floatbowl overflows.

Excess fuel entering a bowl is supposed to escape through an overflow nipple at bottom of the bowl -- not rise up further in the carb.

Usually there are rubber drain tubes connected to the nipples and routed for exit underneath the bike.

When the overflows are properly functioning, excess fuel should drain out beneath the bike, and not rise up into the carb throat to migrate into the crankcase.

Where excess fuel is rising up into the carb throat instead of escaping through the overflow circuit, it indicates that the overflow is clogged or blocked.

Such overflow blockage may be inside the carb or due to a kinked or pinched or plugged drain tube.

Would first check the drain tubes to assure they are clear and unkinked.

The overflow circuit inside the carb is part of the floatbowl. Cleaning it entails removing the floatbowl and assuring clear passage down and through the exit nipple on outside bottom of bowl.

Be gentle and don't break the thin brass tube.

A thin wire such as fishline leader or guitar E string is sometimes helpful to gently pick away encrusted flake and varnish.

Wear protective goggles when blasting carb cleaner through the circuit. Spray repeatedly, both ways, through the circuit. Follow with compressed air. And continue cleaning until the overflow circuit is clear.

If carbs don't have overflow circuits, ignore the above, and concentrate on perfecting operation of the float valves (especially the interface between needle and seat) and the floats.

And in any event, be sure the petcock is preventing fuel flow whenever the engine isn't running.

And do install an accessory aftermarket inline fuel filter, two of them where the carbs have dual fuel lines.

Good Luck!