Compression should be done with all plugs out. Little change with oil shows rings are fine. Problem is with valve-sealing. Might be fried exhaust valves from lack of maintenance previously.
Boots between airbox and carbs won't affect vacuum levels because it's before throttle-plates. It's restriction of throttle-plates that generates vacuum between throttle and intake-valves when pistons are on intake-stroke.
Did you verify alignment marks on cam-sprockets and that lobes point in proper direction at TDC?
More measurements needed:
1. battery voltage with everything OFF,
volts = ??
2. battery voltage during cranking,
volts = ?? too low of voltage will kill sparks
3. key ON, kill=RUN, voltage at coils' red terminals,
volts1,2=??
4. verify spark. Remove plug-wires & plugs. Insert plugs into wires and ground case of plugs to bare metal on engine. Crank. Do you seen
bright blue spark?
5. Now that you have
some vacuum, re-measure petcock flow-rate to see if that amount is sufficient to fill carbs. Disconnect fuel hose from fuel-rail and aim into measuring cup. Crank for 10-sec. How much petrol did you collect?
cc=???
Extremely difficult when there's little vacuum and low flow to get fuel into carbs if it has to flow uphill. Once things are moving, it's fine. But if you can't even get it moving, nothing's gonna come out. It's like syphoning petrol out of auto's tank. Have to overcome that uphill section by applying external forces. But there's no petrol pump on this bike to get past that any uphill leg of journey. Downhill or horizontal only.
6. isolate tank, petcock and carbs from fuel-delivery. Use squirt-bottle to spray 2-3cc petrol into airbox. Wait 15-sec for it to vapourise. Crank engine.
Does it start & run?
