2000 suzuki rm 125 compression

[josh]

How much compression should my rm 125 have? My bike got harder and harder to start and finally whould not start at all. I put in a new piston and new ring but still it wont start and only has 100 pounds of compression. Should it run with only 100 pounds? Any information whould be usefull. Thank you

[psychobilly]

it should run on that compression try new spark plug check for spark at ht lead it sounds electrical problem

[liquidplumber]

hey guy. i was reading a manual on my 98 rm125. it gives a reccommended compression of 175 psi. seems to me that if you only have 100 psi with fresh piston and ring that you have not isolated the problem yet. this is just my personal experience speaking here, but after i put mine back together i pinched the inner o-ring head seal and had a simular problem as you describe. also you could have an issue with the lower halves not sealing properly. the manual describes a simular condition as you have when compression is allowed escape thru the crankcase halves. that would be not much fun to repair but it would give you the opportunity to go thru the whole engine while you are in there anyway. with any repair diagnosing is the most important and most difficult part. i would suggest that you first buy a manual and learn it from cover to cover and then set about doing the simplest repairs first. 9 times out of 10 the problem isnt the worst case scenerio. also while i would agree that 100 psi should be enough to run on in most engines i would be hesitant to agree that it would work in an rm and it surely wouldnt run well if it did.
i found mine blowing compression into the water jacket. which you would probably only see if the bike was running. the antifreeze could not be contained in the radiator and would leak out of the overpressure overflow hose (at cap). another easy escape for compression would be out of crankcase seals. if you cannot get the bike to run at all once again it will be difficult to tell where you are losing compression.
i cant discount the idea of an electrical problem as well, however there is no electrical problem that would result in lowered compression.
there is still one other possibility, the manual describes a procedure for checking compression that is different from what most backyard mechanics would do to test compression. make sure that you are doing the compression test properly or your readings are worthless. an engine leak down test would give you some insight into the condition of the crankcase seal. seems to me that it would be worth it to do this test before deciding to tear the engine down for no reason.