1. Do the tank-cap vent mod
2. Measure petcock flow-rate. i.e. cc/min. Post number and if not to spec, get rebuild kit and rebuild.
3. Inspect intake for obstructions: airbox inlet, air-filter
4. Inspect rubber tubes between carbs and head for cracks, leaks. Make sure they are oriented correctly. One end goes to carbs, other to head. Ends are labeled.
5. If you suspect cables, inspect throttle-plate movement. Turn throttle fully open and see if you can manually open throttle more
6. How fresh is gas in your tank?
7. When was last time valve-adjustment done? Measure all valve clearances and verify if they are within spec. Post clearance numbers here.
8. Do compression-test. Post numbers here.
9. What do spark plugs look like? Post close-up photo of their tips. Post how much gap is that you measured.
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