Checking Compression...

[crazy steve]

I should have mentioned also that somebody could check my results on a in-bike installation by simply bypassing the bike electrics and spinning the motor by jumping off a running car/truck. Connect your ground, disconnect the starter lead from the solenoid and apply power directly to the lead...

[Rickrod3]

In my humble opinion

A motor with no exhaust or air cleaner(Steve you mentioned you put a set of carbs on and retested) would allow a greater volume of air to pass through it.
I think this is the cause of the higher compression.
If it were my project I would take an engine that was within 10% do a clean up of the head lap the valves.

Rick

[cywelchjr]

A motor with no exhaust or air cleaner(Steve you mentioned you put a set of carbs on and retested) would allow a greater volume of air to pass through it.
I think this is the cause of the higher compression.
If it were my project I would take an engine that was within 10% do a clean up of the head lap the valves.

If the carbs add no appreciable restriction at cranking speed the exhaust and air cleaner isn't going to add any either unless they are plugged. That's why Steve said I was right, as I contended that at cranking speed it wasn't pulling enough air for the carbs with the throttles all the way open wouldn't serve as any restriction to the amount of air the engine can move at that speed.

I haven't ever noticed (on pretty much any vehicle) the air cleaner or exhaust to cause much if any restriction at idle either, but once you get up off of there they CAN become a factor.

[Rickrod3]

If the carbs add no appreciable restriction at cranking speed the exhaust and air cleaner isn't going to add any either unless they are plugged. That's why Steve said I was right, as I contended that at cranking speed it wasn't pulling enough air for the carbs with the throttles all the way open wouldn't serve as any restriction to the amount of air the engine can move at that speed.

I haven't ever noticed (on pretty much any vehicle) the air cleaner or exhaust to cause much if any restriction at idle either, but once you get up off of there they CAN become a factor.

I see your point CY.
The more air you try to get the the greater the resistance.
Maybe Steve can test the 79 engine with the kicker?

[petejw]

with my engine, when its cold
i get around 90psi compression,
with the carbs and exhaust fitted,
once its warmed up the compression jumps
up to around 150psi.
just had a quick look at my old text book
and it stated that
the engine should be fully warmed up and all
plugs removed before the procedure,
which is the way ive always done the test.