matt81xs
XS650 Enthusiast
whats the procedure for a compression test. Is it done dry and then wet, wide open throttle or not. I want to check mine but i wanna make sure its done right....
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proper procedure for a compression test...
- Thread starter matt81xs
- Start date
Plugs out and throttle wide open...connect compression tester to plug hole.....some say raise the slides too (BS type carbs)...could take the slides out...I don't do either with air boxes and all and get 150 at standard compression if everything is good.........140 would be ok..........let it crank over with the e-start a few times.......
xsjohn
xsjohn
yamaman
xs650 addict
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Hi Matt, all depends on what your looking for........
Ideally start with a warm engine, both spark pugs removed (though they should be plugged in & grounded to the engine to prevent coil damage). Hook up the gauge, hold the throttle wide open & thumb the starter for a few seconds. If you need to kick rather than e start, 4 or 5 kicks should do (just keep going till the gauge stops rising). The vacuum may or may not be enough to lift vacuum slides. Some say to prop the slides open (with vacuum type carbs, obviously not needed with VM's or similar type carbs), others don't bother & get acceptable readings. I'd say maybe leave the slides, if you get a reading of say 135 psi or lower, maybe then lift the slides to make sure that's not the reason for a lower reading.
Ideally you'd be looking for a reading above 135 (150 psi standard) with 5% difference between cylinders.
If you get a low reading, adding a bit of oil through the plug hole can help seal the rings, so if that brings your reading up, the rings become suspect #1
If not valves become the likely culprit!
In either case, a cylinder leak down test will give you more detailed info.
Ideally start with a warm engine, both spark pugs removed (though they should be plugged in & grounded to the engine to prevent coil damage). Hook up the gauge, hold the throttle wide open & thumb the starter for a few seconds. If you need to kick rather than e start, 4 or 5 kicks should do (just keep going till the gauge stops rising). The vacuum may or may not be enough to lift vacuum slides. Some say to prop the slides open (with vacuum type carbs, obviously not needed with VM's or similar type carbs), others don't bother & get acceptable readings. I'd say maybe leave the slides, if you get a reading of say 135 psi or lower, maybe then lift the slides to make sure that's not the reason for a lower reading.
Ideally you'd be looking for a reading above 135 (150 psi standard) with 5% difference between cylinders.
If you get a low reading, adding a bit of oil through the plug hole can help seal the rings, so if that brings your reading up, the rings become suspect #1
If not valves become the likely culprit!
In either case, a cylinder leak down test will give you more detailed info.
matt81xs
XS650 Enthusiast
sounds pretty straight forward....im having issues with a cylinder not firing, ive cleaned the carbs but the float/needle were really corroded so it may still be suspect. ive been told to just swap the plug wires and see if it follows but im still not sure how thatll work, single coil with the cdi box. If i were to do that wouldnt it start misfiring?? this bike sat for a bit before i picked it up from royfisk, said it ran before he got it and never got to involved in running it so im not sure of its status. I figured a compression test would ease my mind a bit....engine rebuild guh...
sammy323388
XS650 Member
I have oil seeping out of my carburetor sounds like rings, just put new rings in 3 months ago. Any other idea's?
angus67
Welder's penetrate deeper!!
Did you at least deglaze your cylinder with a puff ball? I just did a top end on a thumper, piston spec'd good, new rings deglazed cylinder, runs stronger as new rings seat in.
