MarkC

Another thought here as to possible cause for the stumble or even shut down when applying carb heat at run-up. After eliminating the usual things like butterfly, leaky exhaust, check the float bowl on that carb. If it has worked loose it can cause the engine to quit because of the additional air being sucked in and making the mixture too lean. When the float bowl was loose on mine I would see excessive RPM drop at run-up.

Wait... you mean you don't have to smartly tap these from time to time?

I don't have any experience with the LASAR mod that you reference, but I am curious to hear more about the issue that you are experiencing. You say that your nose gear has some slop in it. Does that mean that you experience some excess lateral travel of the nosegear on the takeoff roll or landing rollout? Or is this something you only notice when the plane is up on jacks? My plane has a bit of an issue on the landing rollout where it will sometimes try to veer off the centerline and you really have to be quick on the rudder pedals to stay on top of it. It can get pretty interesting sometimes. I have been wondering if something similar to what you describe may be the issue with mine.