2 cycle compression ......
 

On Mar 26, 9:32*pm, "Steve B" wrote:
"Tony Hwang" wrote in message

...







Steve B wrote:
I have a 21cc hedge trimmer. *A Craftsman. *It hasn't run for a while,
but
the guy swore it was running when put up.

I put new gas in it, and checked the obvious. *It needed a new on/off
switch. *It has spark. *I can't get it to pop, even with shooting a
little
gas into the carb, or on the sponge air cleaner.

When I pull the start rope, there isn't very much "POP" at all. *I mean
resistance that would come from good compression, or from firing and
igniting the gas/air mixture.

Just how much "POP" should be present, even if you have the switch off,
and
aren't trying to start it, but just basically see how much compression it
has? *I call "POP" that instantaneous resistance on the pull rope where
it
would hit TDC, or fire with a spark. *Does two strokes not have the "POP"
that four strokes have because of their different configuration?

Tomorrow, I'll pull the carb and see if there's anything obvious there..
The
primer bulb worked, no leakage, and filled up, presumably feeding gas to
the
carb.

Steve

Hi,
Take a look at the spark plug. To check a compression I remove plug and
plug the hole tight with chewed paper ball. When you pull the cord, it
should pop out. Is choke working? Try new spark plug or heat it on the
range heater and make it dry. Hope you did not mix in too much oil.

Plug is absolutely new and dry. *Even when I shoot some gas into the carb
opening with a syringe. *Even with shooting a small amount of gas into the
plug hole, reinstalling plug, and pulling cord. *I suspect I need to take it
off tomorrow and see what's up.

I got an edger going today, a 3.5 hp Briggs, but it doesn't run very well,
and the thing will only run with both jets at about 3/4 turn open. *Can't
get it to run up to very high rpm by adjusting the jets. *Took off the
diaphragm cover, but just the cover. *There was sand. *I didn't have a
replacement diaphragm, and that one was on there pretty tight, so chose to
just leave it alone, thinking it might run. *Obviously, I need to get a carb
rebuild kit and go through it. *First, though, I'll take a razor knife and
see if I can get the diaphragm/gasket off, and clean behind it, then reuse
it.

With these little carbs, just a little bit of junk will make a big
difference. *They're like working on watches.

Steve

Compression may be the problem, but you have to run a compression
check to verify. Plugs can be what we call "gas fouled". It may be
new, look clean and may even produce a little spark. But more times
than not, a person usually floods a 2 stroke to the point of "gas
foulding a plug". They think that they can't put too much gas in to
make if fire and usually there is so much gas laying in the crankcase,
it is near impossible to get the air/fuel mixture into the flammable
range.

Here's my suggestion...........

Remove the plug and pull the start cord a few times and let it sit,
come back an hour or so later and pull it a few more times. This
should remove any gas that is in the crankcase. Let it sit overnight
with the plug out. This will let any gas in the crankcase to dry out.
The next day, install a NEW plug after squirting a little juice down
the plug hole. Don't choke, it should fire if there isn't a
compression problem.

Hank ~~~~~ thinking it is badly flooded