Compression testing

[Froggy]

I was trying to figure out my hard starting problems on my 20116 LTX LE after upgrading the starter relay and replacing all the relays in the fuse box except for the shifter relays and replacing the battery which did not help at all. Was wondering about the valve clearances so I decided that a compression check was in order. Proceeded to check compression on a warm to the touch engine that was parked in a heated garage after a 60 km ride roughly 3 hrs earlier. Engine was cranked with kill switch off and throttle wide open. #1 PTO 150 psi, #2 165 psi and #3 MAG 175 psi. Not very impressed as manual states 213.3 psi and 14.2% of each other cylinder. Machine has 16500km. Engine stock except for stingrays air box mod and big Venom clutch kit with 911 cover.
Went and checked the wife's 2015 LTX DX which has 14000km with warm engine and got 180 psi across the board? Manual states full cranking RPM with decompression system active? Did I do this right and any thoughts from anyone would be greatly appreciated.

 

[FrozenTows4]

The 7000 series Arctic manual does not mention a decompression system. Since all spark plugs are removed, it's already decompressed. 10% tolerance is stated.

You did it right. Unfortunately those numbers are low, and out of tolerance, on yours.
Your Wife's is consistent, but still a little low.

Would be interesting to compare the readings of a stone cold engine, to one at normal operating temperature.
A leak down test, at cold & hot engine temperatures, will give a better picture of whats going on.

 

[cannondale27]

The variance from cylinder to cylinder is troubling and sad to say I agree something is goin on. Been avoiding this myself.

 

[Mitch Desorcy]

I'm not sure but would valve timing be a problem if compression is way off??

 

[cannondale27]

I'm not sure but would valve timing be a problem if compression is way off??

If timing is way off it would. I am thinking we are going to need a thread with a form like shock specs or clutch specs. I have seen many compression guages that were out of calibration and maybe Froggys first two tests the cylinders were washed down with fuel. Hope it’s something simple.

 

[74Nitro]

Why not use a leakdown tester? I actually prefer it, by far, over a compression tester.

 

[Yamajon1]

I would put a squirt or 2 of oil in all cylinders and retest to eliminate washed out cylinders and if still uneven or low then do a leak down test. Tight valves can cause low compression cause they are not seating and sealing properly.