Topic: '74 750 k firing on all cylinders but 4

[eliasjklein]

Hello there, so just finished putting together my cb750 (1974), full resto, new cam, pamco elec. igntion, plugs, wires, coils, the works. For about a week it was running fine then number 4 stop firing, the exhaust is not nearly as hot as the others, I have pod filters and a 2 into 1 exhaust, running 120 main jets. Will a new spark plug fix the issue or is there another problem I should be looking at? Like the number 4 carb? I'm all out of ideas. Thanks for reading.

[seanbarney41]

Have you checked for spark on 4?

[neilc]

sounds like plug,do you have a spare to try

[70CB750]

Your spark plug cable is freshly cut too?

[eliasjklein]

I went to get new plugs and they should be here for Monday, the new wires are new and quite long, I could try re cutting them see if that helps, I've put in a few new plugs already, it seems to be fouling them

[kpier883]

If they are black and sooty you might be running rich.  I have a stock '74 except for aftermarket 4:2 pipes.  It fouled plugs regularly (with 110 mains) until I went to 105s.  MPG improved too.  In my case I also changed the #40 idle jets to a smaller size because it never needed the choke to crank, which indicated rich to me.   

[eliasjklein]

I got it running nicely now, new plug did it, running 120 mains, air screw is backed way out, I think its still running rich though, I've heard with pod filters it will run a bit leaner