Compression question

[awafan]

I have a '72 xs650 which I am trying to bring back to life without a major engine teardown. I am almost done but have a couple of questions regarding the engine.
I did a compression test and have 145 on one side and 115 on the other. From my experience 10% difference is ok so I know thats out of spec. Here are my questions.
If the bike is not going to be a daily rider, can I let the compression slide until winter when I can tear the engine down?
Has anyone had any luck using oil additives to gain some compression ie Lucas oil additive?
How much compression will come back after running the bike like this?

 

[Max Midnight]

It depends what is causing the issue.

Try a squirt of oil into the offending bore and re-run the test. If the compression improves then this would suggest that it is a piston ring issue.

If it stays the same then it points to valves. Bring the motor up to compression and listen in to the inlet and exhaust ports for the sound of escaping air.

I have seen Forte Oil Treatment used to good effect on a car. It improved the compression readings and the improvement was maintained.

If I could predict what effect it will have on your motor then I would probably also be able to predict lottery numbers. Sadly for me I can't so I can't say if it will help.

So what is the possible effect of leaving it?
If it's sticking rings then probably not a lot although you will be getting unwanted blow-by which may pressurise the crankcase and will contaminate the oil more quickly.

If it is a broken ring this could score the bore and even junk the barrel.

A valve not seating could burn which would probably involve additional cost to rectify.

Your motor is trying to tell you it's poorly. If you leave it then matters will get worse so if it were mine I'd dive in now and fix the issue.
At least that would be one less thing to worry about.

 

[gggGary]

Given that you are going to ride it; put some compressed air in the plug hole listen to where it's coming out. Tell us, we can then give a some ideas on what to do.
I would spritz some rust buster in the cylinders and kick it plugs out a couple of times, let it sit over night. Then a small squirt of oil, kick a few more times put in the plugs and ride it.

 

[XSLeo]

How long did the bike set idle before you started working on it? If more than a few years, do as gggGary said then ride it. Often after an engine sets it forms rust in the cylinders and on the valves. This can cause low compression. After you ride the bike 50-100 miles the rust wears away and the compression comes up.
Leo