HI all. Long time rider, first Harley. I picked up a 93 FXSTC a while back. Has drag pipes on it and finally got some baffles for it. My issue I've noticed the other day is a weird miss fire. Front cylinder seems fine but my rear cylinder seems to be firing half as much. Front pipe gets hot and rear pipe only gets warm. I've checked plugs and wires and they all seem fine. Any one out here in EVO land that can point me in a direction on what else to check? Any help will be greatly appreciated. Thanks

 

I'd check the intake seals and the coil.

 

Is this at idle or through the power band?

 

If a single fire nose cone ignition has been installed, the ignition has over heated and is droping the signal to fire the rear cylinder.

 

Yes this is at Idle. Noticed of I rev it up a little it's seems to be about the same

 

I'll have to check on this. As far as I know it should be a stock ignition from what I was told. Only thing I've found so far was the pipes were changed and baffles had been removed. I've recently have put baffles back in now. That's when I noticed the difference in the firing between the two cylinders. So damn loud before I didn't notice it

 

Have you pulled the rear plug to have a look see?

 

I had a similar problem with my longshots (they were true duals, no cross over), it was a bad rear exhaust gasket.

 

Intake leaks are as common as cornbread on EVOs. My gut says you have an ignition issue but, a decent leak on the rear intake to head would cause it to really act up too. This is what I would do cause I'm a redneck.. I would get it warmed up, shut it down, pull the rear plug wire, stick a spare plug on it, ground it and hit the start button. Then I would watch to see if the plug was firing as it should. If not you can probably eliminate an intake leak as the issue. It could be as simple as a bad plug wire or plug. If you have a service book it will tell you how to test the ignition system.

 

So if the plugs look fine, is it as in a nice caramel color? If so it doesn't sound like a lean condition. Do a compression test on both cylinders. The rear psi must be close to the front, within 10 psi will get you by and depending on what cam pistons and head work 160-190 psi, if there is a big difference I would look at the possibility of a collapsed lifter or possible rings (compression) depending of miles. Lifters can go at any time. Do you know what your oil pressure is at idle?