engine check list

[trx450jason]

can anyone come up with a check list for an engine that wont run and how to check everything..its for a 93 xr 100 if that matters at all. i just dont know where to start looking for problems

[GPracer2500]

The short answer is:

is there spark?
is there fuel?
is there compression?

An engine that won't run is deficient in one of those three areas.

[trx450jason]

makes things simple. whats the easiest way to check these

[GPracer2500]

Check for spark by pulling the plug and grounding it on the head or cylinder somewhere. Turn the engine over and look for a nice strong, blue colored spark between the ground strap and center electrode.

Regarding fuel: first make sure there's fuel in the float bowl. If there is, then make sure the carb is internally clean. If a jet is clogged then fuel might not be getting from the bowl into the engine. Another thing you can try is spraying starter fluid into the engine through the carb. If it will sputter to life with starter fluid present but dies as soon as the starting fluid burns off then it's a good bet there is a fueling problem.

For compression, a compression tester is the best way. You can remove the plug and hold your finger over the plug hole and feel for compression, but some compression isn't always enough compression to allow the engine to run. But if you feel zero or very little compression then you know there's a problem there.