The bike ran when I bought, but the brakes were shot and the petcock leaked like crazy.  I parked it and we moved so it sat for a few months.  I pulled the gas tank and cleaned out all the surface rust and installed a new petcock.  Put it back together and couldn't get it started.  My plan was to just get it running.  I decided to focus on getting it started again so would check spark, fuel/carb.  Took the plug out and was getting a spark - although it seems kind of weak.  Decided to check compression while I had the plug out and was getting only 70 lbs.  

So, my question now is; should I pull the engine out and check cylinder, rings and piston? Or, just keep focusing on getting it running?

The bike is in great shape and is complete so it is worth saving.

Thanks.

Compression figures and testing is a tricky subject.
Here’s a thread worth reading, but on face value 70psi sounds too low.
yamaha-enduros.com/index.php/forums/1977...pression-spec#149625

70 sounds low but if you can feel it possitively on the kick start then it'll run. I'm working on the theory that if it ran when parked then it's unlkely anything has changed. Spark can look weak but if it jumps a spark then it should run. Spark can look thin or weak but actualy be good. A bright flash can be less so with a faulty condenser so it's not concentrated & just a flash with no 'bite to ignite'.

Is this a known good compression tester? Lot of the cheaper ones give spurious readings.

That was a good thread and there was a link to a good article on how to test for compression.  I will retest using the suggestions in the article.  Thanks for sending.

It's a brand new tester, but it is a Pittsburg brand from Harbor Freight so...

I bought that same tester and I was testing compression on my snowmobile and it showed I had 70psi in both cylinders but the sled ran great. I then went and checked compression on my freshly rebuilt three wheeler. Same result… compression testers have never really been something I trust. 

I needed an adaptor for my Gunson tester and purchased what looks to be the same set as the one you got from Harbor Freight.
I compared my Gunson tester with the alternative one and the readings on the alternative tester were very low, which may explain why you are only getting 70psi.
In my view those sets are only good for the adaptors that come with them.

Valve core should be 1st to see the cyl. pressure.(no adapters/hoses)

The core is a special low blow-off pressure type, not a tire valve core! approx 1psi

cliff

Throttle open too so it will get a full mouthfull of air.