OK here is a quick update to the problem(s) I'm having on the B20. I purchased new water temp. and cold air sensors on line. These are not after market , but the Bosch with matching part #s. I figured after 35+ years why not just eliminate two questionable parts. The cost was less that $40.00. After installing these , readjusting the throttle switch .setting the timing to 10 BTDC and the idle to 850 it still has a misfire/ backfire at low RPMs under-load. The motor starts hot or cold with no hesitation and idles down after warm up. One thing I did find that would soon have become a big problem was the filter in the gas tanks was fighting a bunch of loose tank liner that has broken loose from the inside of the tank. About 7 years ago when I purchased the ES it had pin holes leaks from rust and age so I opted for the JC Whitney gas tank repair kit . It has served me well, but the has taken it's toll on this linen and will need to be redone using the POR15 tank sealer this time. Thanks for the advice and Ideas on the problems I'm having on the motor ,and yes I'm still looking for the answers.