Just a reply about the Video on the different comp testers ,I can't believe how much of a difference he got with the 2 readings,I suspect the o ring was leaking on the cheaper red box tester as he said he only tightens them finger tight so it could have come loose or compression leaked past the o ring as I've had the o rings leak compression before on testers unless I tighten the plug hole fitting with a socket so it's tight.
When I tighten the tester tight in the threaded hole the O ring eventually fails and needs to be replaced but now I have just installed a spark plug washer on my comp tester threaded connector.and that should last for ever.
The longer the flexible hose the more your reading will be down from the correct reading if the Schrader valve isn't at the spark plug end on the compression tester with small engines.
I checked a Victa 2 stroke 160 cc motor ,the short comp tester has the Schrader valve at the end that goes into the head of the motor and the longer tester has the Schrader valve up the other end near the gauge.
I get a reading that is 20 psi different with the two comp testers (longer tester is 60 psi ,short tester is 80 psi)
I usually like a small motor to be on at least 50 psi with the longer tester so that may be 70psi for a cold reading and is the lowest I will use a mower ,I find the mowers can still last 10 years but can stall a little easier in long grass,they will start straight away after stalling hot but find any lower comp reading and they can be a pain to start hot after stalling in longer grass , most people prefer at least 85 psi as a lowest compression reading.
The short tester may be a little low reading also because you are still making the combustion chamber bigger with this tester than if you had a spark plug installed.
