compression

[39NESP]

hi all does any one know what compression a 1999 25 johno should have
cheers snap

[tunaticer]

Mine ran at about 110-115 psi.

[gazza2006au]

Hey Nes i donno what the compression should be but disconnect your throttle open the throttle wide open remove all spark plugs

Now test each cylinder

They should be winthin 10% of each other also compression tester brand from brand can give different readings

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[Mopheus]

Here's a searchable copy of the manual:

https://www.dropbox.com/s/14py8z93as...anual.pdf?dl=0

No factory spec on compression - just all cylinders within 15PSI / 100kPa at operating temperature.

[gazza2006au]

I think its a bit more than that Moph some engines i have seen are about 70psi and some vary up to 175psi

These little engines are around 80-115psi im not actually sure how the pressure is calculated bore or stroke wise

I think i recall reading the optimax run those high psi numbers

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[Mopheus]

I think its a bit more than that Moph some engines i have seen are about 70psi and some vary up to 175psi

"within 15PSI" means each cylinder tests within 15psi of the others, not that they're running at 15psi.