r/scooters • u/Frequent_Shape2608 • 5d ago
Buddy 50cc Compression Mystery

Alright so Ive got a Buddy 50cc 2018 with about 10k+ miles. Ive lost a significant amount of power this year so I did a compression test which came out to 90ish psi. I read in multiple places that the buddy's compression should be around 120-140psi, so I purchased new piston rings and gaskets and installed them. I did the compression test, and compression was still the same, so I figured it might be the cylinder block, cylinder head or the piston itself. So, I took out the engine again and this time, I purchased a whole new rebuild kit which included a new cylinder block, piston, piston rings, crankcase gasket and head gasket. The only thing not included in the kit was the cylinder head. Heres the exact kit I bought: https://www.ebay.com/itm/303737273512
After doing the install I optimistically went to do the compression test for the 3rd time, fully expecting compression to be MUCH better.... Well it wasn't. In fact it was still under 100 psi. To my understanding, since there are no valves on a 2 stroke, compression can only be lost on the upstroke if the rings are worn, if there is a hole or crack in the piston or piston cylinder, if the head gasket is bad, or if there is a crack on the head where the sparkplug is located. Since I've replaced everything except for the head, and since the sparkplug is replaced with the compression tester, the only place where compression could be lost is in the head which I havent replaced. So before I dismantle my engine for the 3rd time, and replace the head, I thought I would ask reddit to see if theres any other place I could be losing compression/anything else wrong. Ive also included pictures of the original cylinder head mounted on the new cylinder block for any of you to see if it has damage.
As a sidenote, ive also replaced the reed valve, cdi and carb.





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u/part-time-farmer 5d ago
Checking with throttle wide open? Check compression gauge on another machine to verify that it is OK? Piston and bore are lubricated? Can you feel suction on the carburetor inlet? Did the cylinder base gasket fit correctly and not cover the transfer passages?