Compression Test Techno v Evo

[cello]

Just airing this to see what you think , ran a Compression Test on my Techno 97 and got nigh on 170 PSI , whan I had the exhaust off I took a look at the piston and it looked worn and scored but this bike seems to have a lot of compression whn kicking it over and seems to pull very very well low down.

 

Tried a 2014 Evo 250 and only go 110 PSI well it was more like 106 but I rounded up, is this right?

 

I know it all depends on the life that the engine has had but I would have expected it to be the other way round with more compression from the Evo, the Evo does sound a little slappy like th little end is starting to knock so its goinf to have the head off for inspection at some point..

 

I must say the Evo controls all work perfectly compared to the Techno , brakes particulary but I guess if the Evo motor is good it should pull hard in all gears even the high rato 4 and 5 but its difficult to test round where I live as the bike is not road legal. Is there any road test I could do to test the motor out as I dont want to DNF because of the motor notfiring up or not pulling up a hill in a wet soggy trial New Years trial I'm thinkin of entering.

 

TIA

[konrad]

A lot of factors go into making an accurate compression test.  A few things to think about: 

Compression must be tested with the throttle held wide open.

I usually keep kicking until the gauge stop rising. This can often be a dozen kicks.

The spark plug adapter you use can make a big difference if it increases the combustion chamber volume appreciably.  For example, using a short-reach adapter in a long reach plug hole gives inaccurate (low) readings. 

If the piston crown and/or combustion chamber has a large about of carbon buildup, this will increase the reading. 

Smaller cylinders tend to have higher cranking pressure than larger ones. 

The barometric pressure (altitude) will affect the exact number.

A hot motor will make more cranking pressure than a cold motor.

Oily cylinders tend to make more pressure than dry ones due to a better ring seal.

There are other factors too.  

[feetupfun]

One way to judge piston ring seal without pulling much apart is to inspect the cylinder wall via the exhaust port or the plug hole, looking for dark areas (carbon). Carbon on the walls indicates piston ring blowby. 

Be aware that trials two strokes nowadays commonly suffer from having the rings stuck in their grooves by gum and carbon. This can happen quite quickly depending on how the bike is ridden, the type of premix oil and how well the bike is jetted.