TOPIC:

I'm having starting issues with a bike that has sat for ten years. I didn't think 120psi is too low to keep it from starting, but it may be. The other cyl is 150. It has new coils, wires, plugs, battery, contacts, condenser, etc and has power and spark. I'm shooting directly into the carbs with start spray and it isn't catching. The spark is weak, but it's there. 

So, marvel mystery oil.... Or is there something better and more likely to unstick the ring before having to pull the head?

Side note: i have limited experience with valves. I saw them all moving through the full range, but didn't measure them. What's the best way to measure valves? I have the tools (micrometer, gap gauges, feeler gauges, etc) but usually use them on something else, not valves. I have set valves on my truck, but never had to work around the tiny head in my bikes. Is there room to do it by just taking off the cover and gas tank? 

120 psi is more than enough compression to run.  Below 100 is where you start to have issues.

There are free manual downloads available for your bike.  It's absolutely critical to adjust the valves per the manuals procedure or engine damage will occur.  

On my KZ1100 I could easily adjust the valves with the tank, valve cover and coils off. I imagine the KZ750 should be able to  as well. 

Make sure the compression tester you are using has a valve in the tip. The one from Harbor freight doesn't and it can throw off your results.

Seafoam motor treatment.

Weak spark may be the problem. First suspect is the battery. Yes, even a brand new one can be faulty. 
After you are sure that the valve lash on each valve is within factory specification, then have the battery load tested and whip out your favorite multimeter and find out why the spark is weak. Probably it is the result of dirty or corroded connectors along the way. A high quality contact cleaner like Deoxit, and some small brass brushes will do wonders.
If you have a sticking ring, it will almost surely free up once the engine is running. Be sure to feed it some clean, new oil that is appropriate for wet clutch engines.

Marvel Mystery Oil mixed into the gas works well to free up stuck rings.  I was told this by some engineers that worked for the old Saturn plant in Tenn.  The Saturn 4 cylinder engine was configured with special piston rings for fuel economy reasons and they were prone to carbon sticking, and the MMO helped free them up.  Again though, I doubt that's the reason at hand regarding this particular bike.

I assume you mean the motorcycle sitting? For a short period of time? How do you think a ring is stuck?? Is it a valve at the seat? Carbon?
But Marvels is the best stuff going overall! I have been using it for 40 plus yrs. I am 60 now.
Mix some marvels with Laquer thinner or acetone 50/50. pull plug and fill up the cylinder with a bunch and just let it sit for a week.

When you do get it running, just mix it in your gas and run it! I put it in everything I have! Old Harley Shovel head with soft valve seats made for leaded gas. My lawnmower, snowblower, weed whacker and my 2008 Ford F150..
I love the stuff.

Well, I'm listening..... I can't find a reason the bike won't start. Everything electrical is new except 1 single item, the VR. It passed the test. Valves were done and are set dead on. Pulled the entire harness and cleaned every connector. I have voltage everywhere it is supposed to be when it is supposed to be there. I set the contacts on the new points and made sure the timing was hitting on the mark. 

Pulled the gas tank and airbox to get a direct line to the carb openings and shot it with starter fluid.........nothing. Not even a backfire. Here's a video of the spark. It's weak, but it's there. I should be getting SOMETHING out of the bike. Video doesn't make it look weak, it's very hard to see the spark off video.

Uodate: I removed the carbs completely and direct injected starter spray in the head, still nothing. The timing advance must be to blame?? 

If you have a spark with correct ignition timing and pointer gap/cam valve gap and timing try to spray some break cleaner(fuel) into the air filter housing/carb inlet.
The engine should start for some seconds.
If your engine start with the break cleaner you have a fuel/carb problem you have to search for. If not your ignition timing/sequence or cam timing is wrong.

Took the timing advancer out, moves freely. No issues. Top dead center on the piston is at the timing mark. 

I rebuilt it anyway and made sure it was cleaned and lubed. I  also figured out it is possible to put the cam on backwards so it closes the contact points when the F mark hits. I caught it before I got it tightened up and back together, but that would have sucked.

SIGH. I've touched every inch of it for the last 2 days and everything is dead on. There is literally nothing that should be keeping it from running. 

Valves set to .20mm Factory spec is .17 to .23
Contacts are set at .4mm gap, as per spec.
Every connector cleaned on the entire bikeIgnition switch serviced
VR checked and verified
Timing marks and advance set
Spark on both plugs
New plugs .7mm gap
New ignition coil
New boots and caps
New battery
New contacts
New condenser
Removed the carbs completely and shot start spray into the head, not even a wiggle. Nothing. Bypassed the start/run switch because I found a voltage drop of .5v in it after cleaning it. 
Compression on left cyl went from 120 to 130 after valve job. It was at .14 which is slightly tight. Right side, no change. Still 140.

Can't blame the carbs with start spray, can't blame them if they aren't there! Any engine like this one will run on start spray and no carbs. From there it's just valves spark, but I have spark, and I have valves adjusted perfect. Not guessing I've watched them move full range and retested their clearance 3 times after rotating the engine. They are seating. Timing on the contacts is dead on. I built the timing advance from nothing to make sure every step was on mark. It loses contact at the F mark and gets it back on the half rotation. Advance moves freely like it should and closes completely. I'm completely stumped.

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