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I purchased the st100 string trimmer with the 192cc engine.

from the git go it starts with 2 pulls just like the manual says.
the manual says it will always start on 2 pulls, hot or cold.
In fact the "2 pulls" is part of the warranty.

When i shut it down for a few minutes it does not start with 20 pulls.
It will start (2 pulls) if I let it sit for awhile.
This is an auto choke, no primer.
I took the first one back to the dealer, it did the same thing

I am using regular gas (not E85).
It has been suggested that I should use Premium gas.

Any ideas?

yes, you will get all kinds of advice regarding octane, i use 93 octane in all outdoor power equipment with a quality brand fuel treatment, no problems. in fact most outdoor power equipment operators manuals will suggest octane to use, i believe most people do not read manuals, just add gas & oil & go full throttle.

mechanic mark said:

yes, you will get all kinds of advice regarding octane, i use 93 octane in all outdoor power equipment with a quality brand fuel treatment, no problems. in fact most outdoor power equipment operators manuals will suggest octane to use, i believe most people do not read manuals, just add gas & oil & go full throttle.

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Thank you for the tip mechanic mark.

I will give that a try. I have been using 89 octane and have not had any problems in my Craftsman or Gravely but they are not very new.
FYI the manual for the trimmer says to use 89 octane, but I'm going to try 93 and see if it makes a difference.

I just don't want to wait 20 minutes every time I shut down to move something, etc.

You need to determine whether you have a fuel or ignition problem. Next time it won’t start, check for spark. You may have what is called a hot open or hot short.

We only have California and their emissions nonsense to thank for these problems. The engine is set to run as lean as possible, and only at maximum rpm, so the engine cannot get enough fuel to restart when warm because both the choke and throttle are open. With both being open, there's no way to produce enough vacuum to properly draw fuel for start. Now, the choke is supposed to be partially closed to allow fuel draw for a hot start, but we know this doesn't always work.

So, since my Cub has the same problem, here's my solution. I use a 6" piece of 5/16 I.D. fuel tubing to hold the choke shut for hot starting. See the pictures below. After engine starts, I pull the tubing out and off I go. The tubing will store tightly between the fuel cap and engine cover, ready when needed.