Folic213 Posted May 16, 2023 Report Share Posted May 16, 2023 I bought my 85 720 about a month ago that was sitting for 15 years. I put a Weber 32/36 on it and replaced cap, rotor, plugs and wires, fixed a bunch of wiring issues that the PO did and finally got it running. It will idle fine and rev up at idle fine, but as soon as I put it into gear and give it any load it will start to misfire and backfire really bad. Any tips on what to check first? Quote Link to comment
datzenmike Posted May 17, 2023 Report Share Posted May 17, 2023 There are so many things that can cause this. Set/check the valve lash. 0.014" Perhaps a too tight valve. Set the choke partly on and try driving. If this fixes it then you are running too lean. Possibly dirt in the primary jet which will cause leanness. There are 8 plugs so very easy to get two wrong. Worth checking Quote Link to comment
DwayneOxford Posted May 17, 2023 Report Share Posted May 17, 2023 Get adjustable gap spark checker to see how strong fire is. Weak spark will blow out under load. Quote Link to comment
datzenmike Posted May 17, 2023 Report Share Posted May 17, 2023 It might be electrical... As the throttle opens more and more under load, the cylinder is more tightly packed with fuel and air. It's harder and harder for the spark to jump the gap. At some point the spark says "I'm outta here" and finds an easier path to ground. Like a crack in the tower on the coil. Wires, plugs, cap and rotor were replaced. Pull the choke on and take for a drive. Does running richer cure the problem? Quote Link to comment
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