Driving with the enrichener on will foul your plugs. If it is only the rear cylinder, then I bet there is a vacuum leak in the rear manifold to head seal.

 

I hope you were'nt serious about tearing down to check the timing.
You have to pull the carb off and take it apart to clean it in solvent ( soak overnite ) kamazing results. If you have to adjust the low speed mixture you need to drill out the plug when you have the carb off and once you drill it pry off the plug cover and you will find a miuxture screw.

 

Put in new plugs yesterday and ........it seems to be running fine??? WTF

 

Fresh, properly gaped plugs can make all the difference.

 

The plugs were just a few months old with proly 5k miles on the is this right?

 

What did the plugs look like? If they were oily, black and wet, you may have a bad valve seal, or piston ring blow by. If they were dry black sooty, it is running to rich. How has you gas mileage been? Could have a float out of adjustment or needle and seat that is not sealing. The color of the plugs can tell you a lot about how your motor is tuned.

 

They were dry black and sooty....

 

Your problem sounds like an intake manifold to cylinder leak on the rear cylinder if it wasn't the plugs.

Finding an air leak at the manifold is simple. All you need is a can of penetrating oil like WD-40 with the extended straw type nozzle attached. With the engine idling, direct a heavy spray of the penetrating oil at the manifold gasket area and base of the carburetor and also where the manifold joins onto the head. When the spray hits the area leaking, there will be a distinct change in the sound of the engine. If the air leak is major, the change in sound will be quite obvious. Smaller leaks may only create minor changes in the sound.

The engine temperature need to match the times the problem most frequently occurs. If you accidentally spray the exhaust system, you may get a little smoke. The penetrating oil can be cleaned up by washing the bike after the engine cools.

You also didn't mention what low jet you are running, this could also figure into the problem too. You may want to do a compression test to rule out any leaking intake valve in the rear cylinder. Hopefully you don't have adjustable pushrods in your engine or they could be out of adjustment too.

 

Since they were both dry black and sooty, I do not think it is a vacuum leak. It could be that you are leaving the enrichner on to long when warming up. Also, since they are dry it is not oil fouling from the valve seals or blow by from bad rings. I am just guessing, but I think that the back cyl. plug was fouled enough to make it miss when cold, and start firing after it cleaned out and warmed up a little. That is why I generally suggest changing plugs first when doing this sort of thing. Many times its not the problem, but its cheap and a good place to start. I always do the simple stuff first.

 

Jim, thanks so much. I do leave the enricher on till it warms up but, it seems to pull in on its own. Is this not what I should do?