About a mile back on this thread, he said that he found the problem. Someone
had loosened the cyl. head bolts.
"mm" wrote in message
...
On Sat, 01 Jul 2006 19:35:01 GMT, "Tom G"
wrote:


If the carb and ignition, plugs, etc are ok, it sounds to me like a
possible
lack of compression to pull the gas into the cylinder when cold. I've
found that on the old B & S engines, it's necessary to pull the head now
and
then and clean off the carbon. If the rings are ok I think a carbon build
up will also affect compression.

How would carbon affect compression? Unless it keeps the valves from
closing all the way, carbon deposits increase the compression ratio.
They don't decrease it.

I too used to clean the carbon off the top of the piston and maybe the
inside of the head, but that carbon just decreases the size of the
combustion chamber. The displacement of the piston remains the same,
so the compression ratio is higher the greater the amount of
deposits**.

Could cold rings and valves not seal well enough, so that the intake
stroke didn't suck as much air in? I don't know. But that seems
unrelated to compressoin.

**If I recall correctly, in mowers or cars, this can lead to
detonation, running on, and knocking, because hot spots in the carbon
ignite the gasoline vapor in addition to the spark plug doing so. But
that's only after the engine has heated up. So carbon deposits can be
bad, but unless they keep the valves from shutting, I don't think they
can cause lack of compression.



Tom G.