I guess I was bombed for putting a link to a possible answer in another forum. Here's part of the content: This motor uses an enrichment system called Prime Start. There is an additional fuel passage that allows more fuel into the mixture for cold starts. After about 5 minutes of run time this passage is closed by a needle valve that is actuated by the charge coil voltage going through a heating coil. So it is not a choke as it does not restrict air like a choke plate, but it does increase the fuel to air mixture, similar result. Your issue is most likely that either the idle speed is too low or that the air/fuel mixture on the carb needs to be richer. The problem is that the EPA tells dealers that they are not supposed to touch the mixture screw and it is covered by a pressed in plug. Don't twist the throttle, this only adds more air during a cold start. The motor may need a re-start or two, but once it gets a little warm you should be good to go. Otherwise, your dealer may be willing to adjust your carb for you, should be a simple enrichment and you're on your way.