[No dialogue] [Music]
This sparkplug is a little bit blackened, a little bit fouled, you would say. Now the
most likely cause of this is overfuelling or a rich fuel condition. Let me compare it
here to a sparkplug out of my car, which is a very clean burning machine, especially alongside
of my lawn mower. However a machine like a lawn mower sees such dirty service and has
kind of a crude air filtration system. So you’re going to have problems like that.
Reasons for a blackened or carbon deposited spark plug would include things like too rich
a fuel mixture or a sticking choke or a clogged air cleaner, you know, anything that’s going
to increase the fuel in the fuel : air ratio. Also a good possibility is oil seeping past
the rings on the compression piston and getting up into the combustion chamber and fouling
it. So what we’ll do is a quick compression test and have a look and see what kind of
numbers we’re pulling. OK so check it out, on the left we have my
low-range compression tester, on the right my high-range compression tester. The high
range of course is for high compression diesel engines and the low range one is for a wide
range of vehicles and machines including this tiny little four stroke engine we’re going
to give a test to. OK you just push on this spot right here and that releases the lid…
just remove these two screws. There’s another one in behind here. That’s why you need
the long extension on your socket wrench. And as that one comes out it just falls away
like that. OK so we’ll have a look in here. There’s
your money shot right there showing the throttle plate so the procedure here is to put a screwdriver
in this hole to block that open. Whatever you use make sure that it can’t fall in
and it won’t break apart and pieces of it fall in. Put my screwdriver on in there past
the throttle plate and make sure it’s blocked open before I pull on the cord. Thread it
into the spark-plug hole, just do it about like that: hand tight. It’s a good idea
to just put it down somewhere safe out of the way.
OK so I looked around online to see if I could find some technical specifications for this
engine. A new machine like this will make about eighty psi in pressure. Sixty psi on
the other hand is generally agreed to be acceptable. Twenty psi is only a quarter of eighty psi
so that’s twenty five percent. Most mechanics I’ve worked with agree on a range of acceptability
of around fifteen to twenty percent. So twenty five percent is quite generous, now keep in
mind that it would depend on the type of machine. Consensus seems to be that it’ll still cut
grass acceptably under normal conditions even with a twenty-five percent loss in compression.
[Engine turns over] Sorry about the bumpy ride.
OK I’ve done a dry compression test and the results are in we’ve got eighty psi
and its been holding eighty psi for five minutes now.
OK we’re just going to put a drop of thirty weight oil in there. Maybe two shots. Put
the compression tester back in. OK so now with a drop of oil in the combustion
chamber we’ll do a wet compression test. OK now the wet compression test is eighty
psi. This ten year old lawn mower of mine is making the same compression it did the
day it came out of the factory. [Mower starts]