does it happen all the time or on long runs? Could be a heat related electrical problem. Had a buddy with a fatboy that would run awesome, but then on long runs would start hesitating and what not. We banged out heads on the wall trying to figure it out.
i think it ended up being a bad VOES switch. It would get hot and stop working.

 

Even with a 3" tank lift, which I believe alters the tank angle more than dropping the rear 1.5", total range is only reduced by 8-14 miles per tank (from full to bone dry).

My bet is when you put it on reserve you will get more miles out of your reserve than you used to without the back lowered.

Overall you have lost only about 10 miles in total range, just now more of your range is on the reserve side of the equation.

 

Mostly on long runs and at high speeds, 50 and over.

 

Maybe it's a sign to slow down and enjoy the scenary...

 

Is it at a constant RPM range. Like does it seem to stumble at the same RPM range everytime.

When it stumbles can you let off the throttle and slowly get back in it?

Sounds like the carb is starving for fuel. You could be running out of fuel. I am not familiar with OEM harley stuff as everything I build is modified. Do the stock petcocks have the filter? If your filter is restricted it wont flow enough on the top and it will starve the carb.

Had a triumph bonneville that would do the same thing. on long stretches the one cylinder would go lean. Could figure it out but then found out one petcock was restricted and would run the float bowl dry on long stretches.

Hope I didn't confuse you.

 

My guess is that the tank is flaking from using ethanol in the gas and it is clogging the gas screen around the petcock.
This is why it is fine while the bike idles, and when the tank is full (more pressure) but at speed it is starving for gas.
Pull out the petcock and check for paint flakes on the screen.
That many miles/age it should be checked/cleaned anyway.
I believe it is part of the 50k maintenance check.

 

Night Train.....any luck on your issue yet?

 

Thanks... I only get a little over a 100 miles on mine...

Wow I would try the petcock... Think of it as a upgrade... Get your self a Pingel High Flow Petcock??? If it doesn't work atleast it's a performance upgrade. But if you look at what the petcock looks like it could be the bottom is a gunked up and the top flowing good???

Sorry my photobuckets acking up... heres a link... So rebuilding wouldn't be a bad idea either???

http://flyritechoppers.com/Pix/petcock450.jpg