Sophomore Rider
Currently Offline
Posts: 139
Likes: 0
Joined: May 7, 2013 21:44:09 GMT -5
|
Post by david3336 on Apr 7, 2014 16:20:49 GMT -5
how much compression should a stock 50cc 2 stroke have to cranck and run any help would be great
|
|
|
|
Post by skuttadawg on Apr 7, 2014 21:33:16 GMT -5
Around 120 PSI . I had a wristpin come out one night and it went from running great to a sputtering death and would not start . I bought the engine compression gauge from Harbor Freight for 20 dollars . It read  PSI . When I removed the head I saw how bad the clip ate up the soft aluminum head and piston dome . I shaved down the real bad areas and bought a new BBK . I put on the new piston and tried to the old block just to see if it would work and after 3 tries I took it off and put on the new head a cylinder after lubing up the piston and rings . I started the first time and compression was 165PSI . I only had it run for a few seconds and gave it a sip of throttle to see if it would rev up . I had the pipe off as to why I did not run it but for 10 seconds . A warmed up engine should give a higher PSI reading than a cold one . Make sure to screw in the adapter tight and have the throttle at WOT ( wide open ) before hitting the starter button . Rings do not last that long on a 2T so if you have many miles and compression is low new rings and a head gasket will perk it up . Depending on wear you may need a new piston also and might as well install a new one while it is apart . You can get a rough idea by pushing down the kickstart by hand with the sparkplug in it and again with it removed a finger over the sparkplug hole . Old gas can gum up the tiny holes in the jets so I would remove the carb bowl and unscrew the idle jet and main jet . Use any carb cleaner spray and a stiff solid wire to poke through the holes . If it has an oil injector is the tank full of oil ? Some have a kill switch in the float level of the oil tank to prevent running it while put of oil . Remove the sparkplug and lay it against the head or frame to get a ground and see if it sparks . Cheap 2T oil can easily cause oil build up on the plug and cause it to foul out . Carb spray and a piece of sand paper folded over can clean the electrode and prong . May need the gap reset too . Reeds can go bad to and cause it not to run . The reeds and on the bottom end of the intake inside the case . |
|
|
|
Post by alleyoop on Apr 7, 2014 21:45:28 GMT -5
Yes, at least 120PSI if the compression is lower than that some may not even start. Although I have seen them run with about 100psi but no power whatsoever.
Alleyoop
|
|
Sophomore Rider
Currently Offline
Posts: 139
Likes: 0
Joined: May 7, 2013 21:44:09 GMT -5
|
Post by david3336 on Apr 8, 2014 11:40:23 GMT -5
ok thanks im going to check compression now ill let you know what i find . im not a 2 stroke person Im a 4 stroke man lol
|
|
Sophomore Rider
Currently Offline
Posts: 139
Likes: 0
Joined: May 7, 2013 21:44:09 GMT -5
|
Post by david3336 on Dec 20, 2014 9:39:40 GMT -5
ok got a 2 stroke bike less than 300 mile on it and it only has 92lbs compression it started cutting off while riding a few days ago but would crank back up a few min later and go again it cut off yesterday and now wont crank checked fire and fuel getting both checked compression only like 92 what should i check first im not a 2 stroke guy i work on 4 stroke all the time so 2 stroke is new to me any help would be great
|
|
PSI . When I removed the head I saw how bad the clip ate up the soft aluminum head and piston dome . I shaved down the real bad areas and bought a new BBK . I put on the new piston and tried to the old block just to see if it would work and after 3 tries I took it off and put on the new head a cylinder after lubing up the piston and rings . I started the first time and compression was 165PSI . I only had it run for a few seconds and gave it a sip of throttle to see if it would rev up . I had the pipe off as to why I did not run it but for 10 seconds . A warmed up engine should give a higher PSI reading than a cold one . Make sure to screw in the adapter tight and have the throttle at WOT ( wide open ) before hitting the starter button .
..BAD TO THE BONE..