COMPRESSION ISSUE?

A little info first:

1976 kz400
Ran when I bought it.
Had honda exhaust on it, which i replaced with the stock 2 into 1 pipe along with the copper washers.

Now when I kick it over it seems to have no compression at all.

Did I possibly forget to do something or what? I'm lost and running low on prime riding time.

Thanks
-kevin

Juicyk wrote: A little info first:

1976 kz400
Ran when I bought it.
Had honda exhaust on it, which i replaced with the stock 2 into 1 pipe along with the copper washers.

Now when I kick it over it seems to have no compression at all.

Did I possibly forget to do something or what? I'm lost and running low on prime riding time.

Thanks
-kevin

Hopefully the engine wasn't run during the process without header pipes attached, which could have resulted in burnt exhaust valves.

Usually, replacing headers has no effect on compression.

A poor man's leak-down test could indicate the source of compression loss.

Are spark plugs installed? And tight?

Was any other mechanical work done?

Good Fortune!

Are you sure the engine is turning over when you kick it? You're not pulling in the clutch when kicking are you? Ed

650ed wrote: Are you sure the engine is turning over when you kick it? You're not pulling in the clutch when kicking are you? Ed

Haha yeah not my first rodeo, yes it is turning over. Im fully confused how replacing the incorrect exhaust with a stock exhaust does this.

Im going to mess with it after I get out of the office today and hopefully figure something out.

I'm not familiar with the KZ400, so please forgive me if this question sounds dumb. When you replaced the exhaust did you need to remove the clutch cable, sprocket cover, or anything else that may have affected the clutch cable? I'm wondering if the clutch is hung up on something and being partially pulled in. On my KZ650 the lower end of the clutch cable seats in the sprocket cover, and if not seated properly it keeps the clutch partially pulled in with no indication of that at the lever. Ed

650ed wrote: I'm not familiar with the KZ400, so please forgive me if this question sounds dumb. When you replaced the exhaust did you need to remove the clutch cable, sprocket cover, or anything else that may have affected the clutch cable? I'm wondering if the clutch is hung up on something and being partially pulled in. On my KZ650 the lower end of the clutch cable seats in the sprocket cover, and if not seated properly it keeps the clutch partially pulled in with no indication of that at the lever. Ed

Nope never got near it.

A leak-down test should help identify source of compression loss.

A leak-down test injects air pressure through the spark plug hole to pressurize the combustion chamber.

Can perform a poor man's leak down test by introducing compressed air into a spark plug hole and listening to where it escapes from the combustion clamber. This may be done at TDC or any other cam positions where both valves are fully closed. Top dead center (TDC) is when the piston is at its highest position. An easy way to tell TDC is by alignment of the T mark with the case mark when viewed through the timing window.

May introduce a spurt of compressed air by using a rubber cone-tip blow gun (rubber air nozzle) held into the spark plug hole. And of course keep holding it in position to keep air from coming back out the spark plug hole while listening for escaping air at other places. The air compressor should not be running while listening because the noise will likely drown out any sound of escaping air.

A portable compressed air tank may also be used in lieu of a live compressor.

Air heard escaping from the exhaust indicates exhaust valve not fully closing (perhaps too tight clearance or damaged valve or valve seat).

Air heard escaping from carb intake indicates intake valve not fully closing (perhaps too tight clearance or damaged valve or valve seat).

Air heard escaping from crankcase breather indicates loss of compression past rings into crankcase (perhaps worn piston rings or cylinders).

Air heard escaping from head gasket area indicates indicates loss of compression past head gasket (perhaps due to a blown head gasket).

A leaking valve may sometimes be resolved by adjusting the clearance to within specs.

A leaking head gasket may sometimes be resolved by torquing the head fasteners when the engine is stone cold (such as after sitting overnight).

If a standard compression test produces low figures, it may be due to worn rings/cylinder and/or incomplete seal when valve is supposedly closed.

Adding a teaspoon of oil into the cylinder through the spark plug hole, and re-testing, will usually produce either slightly higher or significantly higher figures.

If only slightly higher, or no higher, the compression is probably being lost through a poorly sealing valve.

If significantly higher, the compression is probably being lost past worn rings and/or worn cylinder walls.

This is because the teaspoon of added oil is helping prevent compression from being lost past worn rings and/or worn cylinder walls. But the the teaspoon of added oil doesn't help close a poorly seating valve.

Good Fortune!

Thanks I'll give it a shot.