OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Trimmers and Brushcutters Four Stroke Trimmers & Brushcutters GX25 Compression - What should it be good engine?

gday still sussing out problems with my gx 25 i done a comp test results are dry 30psi no throttle 90psi with throttle wet test with oil 60psi no throttle 120psi with throttle quistion is what should it be on a good / near new engine iv got power and cutting out problems and hard to start at times just fitted a new carby and overhauled fuel system and done valve lash

NM i done more resurch found shes getting tired these are the specs

GX25

NGK CMR5H 0.6 ~ 0.7 mm
(0.024 ~ 0.028 in.)

�Idle: 3,100 � 200 rpm

Oil capacity 0.08 qt.

Compression 131 ~ 159 psi

valve lash IN. 0.08 � 0.02 mm
EX: 0.11 � 0.02 mm

because of decompressors compression reading are meaningless for small engines and have been that way for 40 years.
The only useful purpose is checking it has enough at cranking speeds, around 70 psi to enable the engine to start.
If you logged your compression every time you serviced the engine then you would have a useful plot of the decline in compression over time from which you could determine the rat of wear in the rings.
All compression reading must be done at full throttle opening, anything else is also meaningless.
Wet & dry readings again do not mean much because of decompression at cranking speeds.

A leakdown test is the only thing worth doing.

Now if you want help, be a little more specific about what your problem is.
In fact exactly what are you doing when your problem happens.
Starting problems ? again means nothing apart from you can not get it to start easily.
dose it fire but not start, not fire at all, starts ,revs it's heart out of 2 seconds then stops, snatches the starter rope back nearly ripping your fingers off, does nothing & pours fuel out of the muffler, back fires through the muffler and gives you a heart attack.
Each * every one a starting problem and each & every one has a different cause.

This should clear up what compression should be. It is excerpt from the Honda GX25 shop manual.