Okay so I'm putting a new short block into this MS290 that belongs to a friend of mine. I get it all assembled and fire it up for the first time. Saw sounds lean so I immediately back out the H about a half turn. Now its rich....then lean....then....well.....kinda all over the place. My brain says "Air Leak". So, I now venture down the path of doing my first ever vac/pressure test. I already had a mightyvac for doing brake jobs and I had bought a blood pressure bulb for doing pressure tests as well...just never had used it yet. I sealed off the exhaust and intake with pieces of an innertube. Used the impulse line as a port for the vac. Pump pump pump, won't hold vacuum! Hmmm. Hook up pressure bulb. Pump pump pump, won't hold pressure either. Get the soap spray bottle. Sprayed both crank seals and pumped bulb. No bubbles. Sprayed intake boot and pumped bulb. No bubbles. Sprayed both innertube block-off seals, no bubbles. Sprayed impulse line, no bubbles. Hmmm. Sprayed compression release port bolt, no bubbles. So......where else could the air be leaking?
Spark plug? Oh no....it couldn't possibly be the spark plug could it? Well, as it turns out, spark plugs do leak air when they are only finger-spun about half way in!!!!!
Tightened the plug, reinstalled the flywheel, clutch, etc., fired it up...runs great!
Take-away.....Always re-check everything...especially the obvious stuff!
Spark plug? Oh no....it couldn't possibly be the spark plug could it? Well, as it turns out, spark plugs do leak air when they are only finger-spun about half way in!!!!!
Tightened the plug, reinstalled the flywheel, clutch, etc., fired it up...runs great!
Take-away.....Always re-check everything...especially the obvious stuff!