Had my engine rebuilt this winter, everything replaced except the engine case (wanted to keep matching numbers)

I currently have 850 miles on the motor, and I have just developed this problem:

The rear cylinder is running rough, will backfire on decel and seems to "miss" on a very consistent basis ie it is not random, you can almost pick the pattern on idle. (I know it is the rear pot as I am running "true duals")

I have a new coil, new plugs and new leads, with SE Heads.

Plug is not fouled, and insulator "looks" ok.

Exhaust is tight, with no apparent leaks.

On a quick "goose" of the throttle it will sometimes blow back thru the carb (S&S Shorty)

What am I missing?
Any other ideas before I ride the 45 miles back to the dealer?

Thanks in advance.....

 

I'd put new plugs in, they're cheap, and do a compression test.

 

Ozzie Check the S&S manifold to the heads for possible poor casting ( air leaks ) I've sent 3 back to S&S This was back in 2004

 

Thanks for the feedback...

I'll check both of those and get back.

 

Intake leak would be my first guess. When that was eliminated as a suspect, I'd ask whether you have a single fire ignition...

 

Found the problem.....

Plugs were ok, and I do have a single fire ignition.

The culprit was: the vacuum line from the carb that feeds the VOES had come off. Plugged it back on and no problems!

Don't know why it only affected the rear jug and not the front .....

Any way, all is well, just got back from a ride and all is well.

Who knows.............