Getting about 27 MPG on my 83 FLH with S&S carb.
Carb has been cleaned and rebuilt (my me).
Plugs kinds sooty so went leaner on jetting.
Slight backfire on deceleration now - so I think it is close.
Is this the normal mileage for the old shovel engine?

 

Seems on the low side.
My '69 FLH with a Bendix carb consistently gets in the 33-35 MPG range.

 

Bit low which carb you have an older " B " or the shorter " E " , B's got around 35 average and the E's should roll the low 40's depending a few things and your tune.

Hit S&S's website and read the E setup & tuning guide it's free and easy to follow.

 

LMAO
I knew it was gonna be an S&S Carb...
Everyone always tunes 'em Fat!!!

 

That's because most guys are tuning around the intakes leaks they never fix.

 

Very true, but, even without leaks, most run it too rich...they do work better that way, Unless you know how to Properly tune a Thunderjet equipped one.

 

Yeah they do like a hair fat on a shovel.

 

It is the "E" version. I will check the website for tuning tips. Thanks.
My indie mechanic has a dyno and seems to know how to tune older iron, so that may be another (expensive) option.

Also wondering if there is some other components (not just the carb) that could cause this. Valves? Timing? Ignition?

 

Like TwiZted has said
Intake leaks are the Number one problem
Masked by tuning very Rich

 

You runnin drag pipes by chance?