standupsmorefun

Here is how it started
I have been working on a 1987 650 sx. I bought it from a guy who couldn’t figure out the piston clips so. I had some stock pistons and rings from another ski installed them and put it back together. Fired it up it ran for 30 seconds twice. Idle was low but I thought I has gotten the hard stuff done and moved on to other projects while waiting for warm weather.
When I went to fire it again a month later I couldn’t get anything except one loud back fire. Did a compression test and it was only 30. I broke it down to the pistons again used a different stock set, block and head from another ski. Still no fire but got one backfire again. New compression was still low at 95 but this should still fire until I can get a new head gasket ( I think that’s my problem given I reused it… I know I know but I cant just walk into the store and buy them).
I don’t now what to do from here I cleaned the carb and all looks to be good there but I am no carb expert I just follow what the you tube videos say. I have resorted to even dropping gas into the carb and still nada. Spark is good my only guess now is timing but I have never had to check this and don’t know how can anyone please help