1987 merc 80 hp missing
 

I have changed out the plugs, and took each plug out and put it up
against something metal so that I could see the spark. Everything
looks good, but I have a miss. where do I need to look next?

Is one cylinder significantly cooler than the other?

Does shorting one plug make the engine stop?

There exist spark plug testers which test the plugs under (air) pressure
while you watch the spark. (Visit the maintenance shop at your local small
airport if the corner garage doesn't have one.)

Roger

http://home.earthlink.net/~derbyrm

"Clamdigger" wrote in message
...
wrote:
I have changed out the plugs, and took each plug out and put it up
against something metal so that I could see the spark. Everything
looks good, but I have a miss. where do I need to look next?

Just a stab in the dark, but just because a plug gets a spark outside the
combustion chamber, does not mean that it is getting a good spark INSIDE
the combustion chamber. I think I remember hearing of some kind of
adapter that allowed one to see if there was a spark when under
compression in the chamber, sort of an clear extension tube that screwed
into the spark plug hole and then the plug screwed into it. Some plugs
fail when under compression. I would not rule out the plugs or ignition
system at this point. If with NEW plugs and wires you still have a miss,
I would suspect a sticking reed valve for the offending cylinder next or
carbon blocking the valve from closing fully. Have you done a compression
check on the cylinders? Low compression will also show up as a miss.

Not to be a 'smart ass', but HOW OLD is the gas? Does it have any
'preservative' in it {such as 'Stor-N-Start', etc.}?

A lot of times small problems like this are due to 'stale' fuel, or fuel
left in the carburetor bowl that deposits gum, varnish, and other 'junk'.

Regards & Good Luck,
Ron Magen
Backyard Boatshop

wrote in message
oups.com...
I have changed out the plugs, and took each plug out and put it up
against something metal so that I could see the spark. Everything
looks good, but I have a miss. where do I need to look next?

Agree with Roger. Had an old British motorcycle which had a maddening miss.
Testing spark under pressure revealed the problem. Lots of wasted time
trying to chase down other causes.

surfturf


"Roger Derby" wrote in message
link.net...
Is one cylinder significantly cooler than the other?

Does shorting one plug make the engine stop?

There exist spark plug testers which test the plugs under (air) pressure
while you watch the spark. (Visit the maintenance shop at your local
small airport if the corner garage doesn't have one.)

Roger