Equally low compression on all 4 cylinders

[Tanerrx]

How did you verify the air leakage from one cylinder to another? Did you put air in one cylinder and the pressure gauge in the adjacent cylinder?

I put cylinders 1-4 on TDC and put my air compressor in 4 and I could feel air coming out of 3. Same with 1 and 2 respectively. No gauge was needed, it was leaking out that much.

[rustybronco]

I put cylinders 1-4 on TDC and put my air compressor in 4 and I could feel air coming out of 3. Same with 1 and 2 respectively. No gauge was needed, it was leaking out that much.

TDC with both valves closed (compression stroke)?

[Tanerrx]

TDC with both valves closed (compression stroke)?

I don't understand your question. What is compression stroke? And wouldn't both valves be closed automatically if it were at TDC?

[tkent02]

Suck squeeze bang and blow.
It's what makes the world go.

[rustybronco]

And wouldn't both valves be closed automatically if it were at TDC?

No. It takes two revolutions of the crankshaft to complete all four cycles necessary for the engine to function. One, TDC both valves are closed and on the other the exhaust valve is open.

Suction
Compression
Power stroke
Cylinder evacuation.

[tom203]

I ......And wouldn't both valves be closed automatically if it were at TDC?

Nope, this is a 4 stroke, it's at TDC twice in cycle ,once for the compression stroke and then at end of exhaust stroke when exhaust is open (and intake a wee bit)

[Tanerrx]

Nope, this is a 4 stroke, it's at TDC twice in cycle ,once for the compression stroke and then at end of exhaust stroke when exhaust is open (and intake a wee bit)

Well ****. I just figured it I were on the T mark that everything would be closed up. I'll give it another try this afternoon when I'm doing a couple other tests.

[mvalenti]

Well ****. I just figured it I were on the T mark that everything would be closed up. I'll give it another try this afternoon when I'm doing a couple other tests.

just curious, why not use a compression tester instead of your compressor and feel?

[Tanerrx]

just curious, why not use a compression tester instead of your compressor and feel?

Did the test again with the pistons and valves in the compression stroke instead of the time around that the exhaust is open and there was no leak coming out of the other spark plug hole. I need to take the carbs and exhaust pipes off with the oil cap off too and do it again to try and listen for leaks properly but I'll save that for another day.

The reason I just did it by feel was because if I can feel the air shooting out of the other spark plug hole I know there is a leak (or thought there was). At that point it wouldn't really matter how much the leak was leaking. It would need to be addressed no matter what it read on the compression gauge. I hope that answers your question. I did use the compression gauge to test the compression earlier and it read low. That's why I went to the air compressor, to find where it was leaking. If that's what you were asking.

Also, my compression gauge suddenly won't hold the needle to the highest amount of compression. So I'm wishfully thinking that my compression gauge if faulty.

[Brendan W]

When you pressurise the cylinder do you lock the crank, cause otherwise she'll turn and start shifting valves.
I reckon/hope it is the tester - the readings are too even.
There is an old RFC preflight check list round here somewhere. It says that if you don't get the full revs against the chocks the inexperienced pilot sends for the mechanic to check the motor, the experienced pilot asks the tacho be changed.

[Tanerrx]

When you pressurise the cylinder do you lock the crank, cause otherwise she'll turn and start shifting valves.
I reckon/hope it is the tester - the readings are too even.
There is an old RFC preflight check list round here somewhere. It says that if you don't get the full revs against the chocks the inexperienced pilot sends for the mechanic to check the motor, the experienced pilot asks the tacho be changed.

The gauge is for sure not working properly. One attachment lets the air back out cause the needle to just bounce up and down and the other leaks air at the rubber part near the head causing it to not get the full pressure. I'm putting some gasket seal around the rubber part and letting it set over night. Hoping it stops the leak. We'll see, just because the gauge isn't working right doesn't mean the cylinders are so I've got to figure something else out.

[BigD_83]

Do you have an Autozone/Pep Boys/NAPA nearby? They might have programs to loan out tools...

[stetracer]

Just wondering do you have C/V carbs on the bike

[Tanerrx]

Just wondering do you have C/V carbs on the bike

I don't think so. Not really sure what constitutes a C/V carb but it looks like it has something to do with a diaphragm and my carbs don't have diaphragms. The only marking on the carbs says Mikuni. Does this tell you anything?

[rustybronco]

A 1979 GS850G uses VM series carburetors.