The old TRX200 quits on me. I had to tow it home. Fortunately, it quit close to home! HERE ARE SOME EXAMPLES of the
troubleshooting job.
Three things are necessary for a small engine to function

1) SPARK: Without a spark at the spark plug..the fuel and air
mixture will not ignite. What I did when my ATV quit was to go
back home and get my truck with my tool kit. I took the spark
plug out and used my test spark plug --see the picture on
this page. There was no spark. I suspected (at this point) a
possible problem with the ON OFF switch. This switch is
located on the left hand of the handlebar. It is the one with
the red button. I took the switch apart and found there was
no problem with the switch.
By now; I had towed the ATV back home with help from my
wife. I used a chain to tow it the short distance up a hill.

NOTE: THE other things necessary to have a small engine
function are:
2) Fuel (GAS) Gas fouling, carburetor clogged or blocked
and blocked fuel filter. Very very common. I have had my
share of these problems. Problems can be greatly reduced
by using proper storage and by using fresh gas and gas
stablizer.

3) Air   Air filter clogged most common.
Above and below picture: the gas tank had to be removed in order to get to the
ignition coil. Gas tank brackets and some of the body housing had to be removed.
Easy to do. A ten minute job. I took pictures of my disassembly in order to document
the task and so that I would remember how everything goes back together.
Below: the gas tank still on. I took pictures to show how and where the  
brackets were positioned.
Keep good notes and draw sketches and/or use your digital camera to
document the task of taking the machine apart. Before I had a digital
camera, I would sketch things out.
Always keep the parts in a good safe storage box. Label or tag the
parts. When adjusting anything, mark the positions first. Extra time
spent doing these things really means the difference between success
and a frustrating time of it.
After removing the gas tank, the coil was now visible and I could
test it. The ignition coil is at the center of the picture. There are 3
terminals. The large one is the high voltage side(the secondary of
the coil). Since it is a high voltage secondary, it stands to reason
that there would be a step up transformation in voltage.
I went on the internet and punched into a search engine:
honda TRX200 and ignition coil and problem. I searched the
resulting returns on this search.
I then was fortunate to find someone else had written about this
type of situation and there was two pages of the TRX200 service
manual posted on a web page..

The primary side of the coil (as measured from across the two
smaller wire terminals on the coil) was supposed to be about
.4 to .8 ohms (or something along those lines). My coil measured
correctly.

The secondary (between the ground-(black coded terminal on the
coil) to the end where it connects to the spark plug ..is supposed to
be in around 4000 ohms.

I measured the resistance slightly above 4000 ohms and so it seems
to be correct. I was told that the coils don't often fail.

I now turned my attention to the electronic/mechanical circuitry
ahead of the coil. It is some kind of electro mechanical device called
the CDI module.
Here's a tip. I was having problems with my
snow blower a few years back. In order for it
to run..I would have to use the choke. The
problem became worse and one day it just
wouldn't run.

When you have to use the choke in this
fashion, it often indicates that the
carburetor isn't working. Most of the time..it
is gummed up. Try running through some
carb cleaner.

One person (mechanic) uses gas stablizer
for winter ..then in the after winter or warm
weather storage season..on the first tank of
gas (and the last tank of gas) he uses a
cleaning additive to the gas.

Fresh gas is a real good idea for small
engines. Try and run them every so often so
as not to let things settle and the gas start
to evaporate out of carburator bowls and
leave behind a varnish deposit.

By far..the snowblowers I have owned have
been the worst culprit for these types of
fuel problems. This is because they often
don't run for months at a time and in the
warm months..the fuel evaporates. For this
reason ..use fuel stablilizer and run the
snowblower the odd time even in summer.
link to next page of the
work I am doing on my
ATV this spring (April
2007)