Number 4 cylinder not firing

[tweeleft]

Hey Guys
I have a SF that runs bad. Number 4 cylinder has black powdery carbon and the other three are fine. Thinking bad coil or plug wire. Can one sie of the 1 4 coil go bad?

THX Jerry

[cywelchjr]

Hey Guys
I have a SF that runs bad. Number 4 cylinder has black powdery carbon and the other three are fine. Thinking bad coil or plug wire. Can one sie of the 1 4 coil go bad?

THX Jerry

Black powdery carbon doesn't sound like a problem with the spark, but you can check the spark easily by taking the plugs out and with them laying against the head verify that you have good spark on 4. You can also swap 1 and 4 wires around to eliminate spark, but make sure to change plugs at the same time as the plugs could be the problem, so put new plugs in, but I would if getting a problem on only one cylinder suspect a carb issue rather than spark which would tend towards a pair of cylinders rather than one, it just sounds like it's running rich.

[bikerphil]

Unscrew the cap from the wire at the plug end and trim 1/4" off and screw back on. It can corrode up in there.

[BA80]

Check your plug and do what Phil said and make certain you have spark. You might swap plugs between #4 and another cylinder and see if the problem follows the plug.

Have you checked compression?

Black soot indicates too much fuel or the fuel isn't being burt properly.

[petejw]

after checking the ignition as the others have stated,
might not hurt to check the mixture screw for a broken tip on that carb,
it wouldnt make it run rich but it would make the cylinder misfire. jat

[tweeleft]

thx guys I'll let you know

[tweeleft]

Found #4 plug cap to have 9 omns not 5. ordered new caps and wires. going to check pickup coils and more today

[cywelchjr]

Unless you have aftermarket coils, the wires are not replaceable without surgery to the coils, and there is a small if non-zero chance of damaging your coils in the process. So unless you KNOW the wires are shot, it's not recommended to try and replace them until you have fixed any other issues first. At least IMHO.

[tweeleft]

Coils test out ok. Cleaned plug caps and regapped plugs. Runs better but haven't ridden and check plugs after ride. will adjust idle mix screws after