Originally Posted by ironhead rocco
Thanks for you help ill do a compression test what should the number be also do you know if the idle air screw on the keinhin carb can be replaced?
The factory service manual should have the cranking pressure listed, as well as the procedures to check it. MAKE SURE YOU HAVE THE PROPER MANUAL BEFORE WORKING ON IT!!!!! I can't remember what it is off-hand. My 1976 was over 190, but then again, I had 12.5:1 compresssion pistons in it. Make sure both cylinders have similiar pressure, at least
within 10% of each other.
Check for intake and exhaust leaks, too. They can cause backfiring. So could worn ignition parts, including the coil, wires, plugs, points, advance unit, weak battery, etc.
Only after checking these things would I worry about tuning the carb. A small leak could have you fiddling with the carb adjustments for weeks! Follow the book for adjustment procedures.
Another bit of advice... if you can afford it, scrap the carb and get an S&S Super E. They work best on those engines.