Hi, PROBLEM: I've a spada that won't start. When I press the starter button the bike cranks fine, once I pull back on the throttle it clunks or makes what I can best describe as a Schhitumph noise. If I crank for a 10-20 seconds it attempts to backfire. It has backfired once. It was running rough so I checked the valve clearances and the done some disassembly on the air filter down to carb level. All was reassembled properly. I'm no slouch but this one has be and a mechanic stumped. Maybe somebody has come across this either with a honda or another bike before. 1. It's getting juice because I've loosened the overflow screws on the carbs and i got juice. 2. It's got plenty of spark on both plugs 3. The Juice is new so no issues with stale petrol 4. The ignition switch is on 5. I've tried both using and not using the choke 6. I've checked the valve clearances, all good. 7. I took the carbs off and checked them, all good. 8. The plugs are new and the HT leads are good 9. Idle and carb settings are set to factory settings 10. Checked both heads with a compression gauge and all is within normal levels there. The schitumph sound can lead to a backfire but that's only happened once, it sounds like it wants to backfire but it doesn't. Can anybody help. Plugs are new, electrics seem fine, head compression are both at 190ish. I can post a video on Youtube if it helps because then you can hear the sound. Well can you help?