Topic: Sudden Backfire

[DuckFan]

Hey all,

So my 1976 CB750F was finally riding great! Rode it to work all last week (10 miles each way). I ride it in today, and it has absolutely no power and jerks back and forth anytime I give it a little gas. It gets up to freeway speed but it takes a long time. I barely manage to get it back home and get to work on checking things. I started with the carbs and discovered the choke on 2&3 were stuck down. I go to restart it and now I have horrible backfire and popping and it won't hold idle and is misfiring a lot. I run a Dyna S ignition and checked all the plug wires and they looked fine. Any ideas?

[scottly]

Carbon fouled plugs on #2&3 caused by the stuck choke. The backfire is from un-burned fuel from 2&3 getting pumped into the 4-1 exhaust and getting lit by the hot exhaust from 1&4. Check the plugs, and if they are black with soot, there's your sign.

[DuckFan]

Brilliant advice scottly! You were right on the money and the bike is running great again! The only remaining issue is I think it's backfiring a little bit when I go full throttle at 70mph. But not a huge issue since my wife gets pissed whenever I even think about going that fast