Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

After having several of these already, I have this one up and running properly in about twenty minutes.  There are several things that I have found that need done before even trying to start one of these engines.   

The first is to put batteries in and TAPE them firmly into the holder, as the batteries tend to pop out otherwise.
Secondly, put a meter on the on/off switch and figure out which direction is on.
The next thing I do is to remove and stretch the governor springs slightly to slow the engine down, set the mixer screw at about 5/8 of the turn open.

And last, but most important, every one of these engines I have found to have the same problem.  The main problem that keeps them from running properly is the the push rod for the exhaust valve sticks in the up position, holding the exhaust valve open, leaving the engine with no compression.  Sometimes it sticks every time or immediately on the first try, and sometimes it sticks intermittently, leaving you wondering why the engine runs and quits, runs and quits. 

The first engine I tried lubricating the push rod and even boring the hole in the guide a little larger.  But the easiest solution is to loosen the two screws at the base of the cylinder holding the push rod guide assembly, as well as loosening the two bracket hold down screws that hold the rocker arm that opens and closes the exhaust valve. 
I put a little Loc-tite on the threads to hold the screws in this slightly loosened position, and this has worked perfectly on every M-91 engine I've had since the first one I bought. 

Anyhow, there have been lots of reviews of tweaks to this engine, so this is just my two cents worth.  I hope it helps someone!