1987 K100RS has a miss

[birddogone]

The above machine has new plug wires and the plugs with about 5500 miles have been cleaned, inspected and gaped. The miss is mostly at idle but does happen at higher rpms on center stand. When I pulled the plug wires while running the bike smoothed out when #4 was pulled, perfect just on 3 cylinders. I wiggled all the wires around the coil and nothing really seems to matter, I think it may be the coil which is original. The miss almost sounds like the starter is trying to engage. Here is a video that may help, kinda hard to hear it until I move to the starboard side. Any help is much appreciated.
Thanks,
Rod in VA.
#67825

 

[timtyler]

Have you balanced the throttle bodies?

Done a check for air leaks?

 

[98lee]

When was the last time the valves were adjusted?

 

[birddogone]

Bike has 65,000 miles on her and the last valve check was about 15,000 miles ago and they were fine then. I've not done an air leak check or have I ever messed with the throttle bodies. Would the miss go away with any of those when I pulled the #4 plug wire? Motor is smooth as silk on just three cylinders at idle when I #4 is pulled.
Rod

 

[yankeeone]

I just went thru that, changed the plugs and that helped.

 

[birddogone]

Well......After switching coils around, re gaping plugs and...taking the starter apart for a good cleaning I finally put the propane to the intakes, and what ya know! #4 intake must have a suction leak because the motor smoothed right out and picked up a couple hundred rpms. So I guess its time to replace the intake gaskets and all the rubber including the fuel hose, vacuum line and the Z hose while I'm there.
Will let ya know how she turns out.
Thanks for the tips,
Rod

 

[birddogone]

Another update........Found vacuum hose going to the presure regulator to be the source of the leak.

 

[98lee]

That's WAY cheaper to fix!

 

[birddogone]

Ya got that right Pard!! Just got in this evening from a 40 mile ride thru the country and she's run'n like scalded dog!!