Motorcycle Repair: kids scrambler, two stroke engines, compression gauge

Question
hi we just bought a second hand kids scrambler the make is maxpro and believe it to be 50 cc. it has got a pull start cord but the trouble is we dont know if  we starting it wrong or whether it not working - it was totally dry of fuel and all when bought .
thanks

Answer
Hi Kirsty,

If the bike is 50cc it might be a two-stroke
engine. If it is the larger 110cc the engine
would be a four stroke engine. The two
engine types have different problems
but some of the basics are the same.

I will assume it is the smaller two
stroke 50cc engine.

You need some pressure in the spark
plug hole to run, this is called
compression and it should blow
your finger off the spark plug
hole if you cover it and crank the engine.
It can be checked also with a compression
gauge if you know any mechanics.

The second thing you need to check
is if the fuel is coming from the
gas tank to the carburetor.
It should run freely if you pull the
fuel line off and turn on the gas valve
on the tank.

Third thing is that fuel tends to clog up
the jets and passageways inside these
small carburetors. You can remove the
carb and get a can of carb cleaner spray
and clean out the carb's insides until it looks really
clean.

The spark plug must be good and you should
have a small spark on the end of the plug
if you remove it, keep the plug wire
on and lay the metal part of the spark plug
against the metal on the engine.
Crank the engine and see if the spark is happening.

You can try a small spray of carb cleaner
or starting fluid in the back of the carb
to see if it will fire on that.
If it fires then you know it needs more work
on the fuel system.

On rare occasions two stroke engines
can develop leaks on the crankshaft seals
that may hinder their ability to start or run.
This can be checked by a mechanic but
is hard to do at home.

So, if you clean the carb, check fuel flow to the carb,
check the spark plug and spark.
Check the compression, try some starting fluid, it should run.
Keep the air filter clean also.

By the way, two strokes need a few ounces of two stroke oil
mixed in the fuel to lubricate the engine.

Good luck!
Wayne S.
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