"Ideal" compression for a '79 KZ400 LTD

I just finished making the DIY air filter (opted for the 3/4" filter pocket, which I recommend others doing as well) for my bike (because like the thousands of others, including 440s, my bike did not come with the snorkel); may not be ideal filter material, but as advice from another guy who has done this, I am running three dark green thin scour pads as my filter media. Running stronger than ever. I only had it running for about 30 seconds until it ran out of gas :laugh: I want to note that I think the scour pads are restrictive enough. The bike cold started MUCH easier, and had no more popping from the exhaust or carburetors (which was caused from lack of pressure/restriction).

I have to admit, it doesn't look nearly as bad as I thought it would (it actually looks quite decent). If it weren't for the shiny metal (aka if it were painted black like the rest of the filter box, which I might do) and green scour pad filter media, I would say it could almost pass for an OEM/factory set up

.

While I was not able to run it until warm (thus testing the warm idle circuit), this got me curious to check the compression of the motor, to see how it's fairing overall. Keep in mind that my bike only has 8,419 original miles on it (and that compression was tested on a cold engine). When I checked, I had the choke plates open (aka choke was off), WOT, and hit the starter. Both cylinders showed the same exact pressure: 125 PSI. Phenomenal? Normal? Less than ideal? What is considered the standard range for compression on these old bikes?

On my 750 twin: "nominal" is about 150, service limit is 115. Check when hot, throttle wide open. There is no spec for a cold engine.

bountyhunter wrote: On my 750 twin: "nominal" is about 150, service limit is 115. Check when hot, throttle wide open. There is no spec for a cold engine.

Well obviously there is no spec for a cold engine. I'm sure there was a ton of blow by being caused from the piston rings' lack of expanding. I'll test again in a two or three days My fuel petcock has been leaking a pretty good amount of gas when under flow, so I ordered a replacement which will supposedly be here Tuesday.