For the first couple years the choke worked like it should on this bike. For the last year it's not been working. It runs a little rich so I've been able to start it by giving it a little throttle and kicking it over a few times with the key off to get fuel in, turn the key on and it fires right up. It works yet it's bothering me. Have cleaned the carburetor several times, making sure every passage is clear, of course paying special attention to the choke related passages.

It's not a big deal as most of the time I'm riding in temps over 80, but what on earth is going on?  I can start it as stated above, with the choke pulled out, but it dies instantly if I let off on the throttle. Put the choke in and it'll idle. If it was rich, I'd expect it to start back up without the choke, but I can kick it with the choke on or off and throttle closed until I'm blue in the face and it won't start. Then 2-3 kicks with the key off and throttle open, turn the key on and it fires right up which makes me think the choke just isn't letting gas pass through. Have experienced the pilot jet being plugged at one point and this isn't the same issue, wouldn't idle at all when that happened. Could the floats be slightly too low? I'm at a loss as it starts easily and idles fine once warmed up to ~100F or more. Once fully warmed up it starts in a kick or two with a little throttle, but again doesn't like to start with no throttle, yet idles just fine with the adjustments at factory spec.
 

 

Darinm: Maybe you are looking at this backwards. The Mikuni carb does not have an actual "choke"(a valve that shuts off much of the airflow into the carb) but an enrichner circuit. The enrichner circuit is most effective when the slide is closed. When you open the throttle, the enrichner is less effective and the overall mixture goes leaner due to the reduced vacuum in the circuit and increase in air to the cylinder. It sound to me like your procedure to start is leaning out an already too rich mixture. I would take a look at the start circuit plunger face to see if the rubber plug in its end looks good and is seating properly.
.Here is a site with an excellent description of how the start circuit works. [code][/codhttp://www.off-road.com/dirtbike/tech/hard-starting-tips-how-to-get-the-fire-lit-18787.htmle] (not sure if I got this inserted correctly)
alnarv

Are you cleaning the tiny starter jet in the bottom of the float bowl well?

 



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A little hard to say with such warm temps, but it looks like I was able to get it sorted. Looking at the assembly, I saw Mikuni later added an o-ring to the "plunger cap" which screws the plunger into the body. Found a small o ring and put it on, and ordered a new rubber "plunger cap cover" assuming mine is too dry and leaking air, not letting the choke get enough vacuum to pull fuel through the enriching circuit. No problem starting with the choke on and throttle off at 70f after adding the o-ring.