I dunno if I've had a couple of bad batches of fuel lately but my stock pan runs normal then shithouse after I fuel up. Change fuel goes ok then shithouse again after another fill. I dunno if its all just coincidence or what

May depend on whether it's the same octane. Newer bikes can adjust themselves after a couple minutes and will (seemingly) change to running on 91 to 98. Your pan most likely can't. If the same octane / brand I don't have any help to offer. It may have been built when leaded or lower octane fuel was the norm. 

Man, talk about opening a can of woims, yeah WOIMS, not worms that eat you when you dead but Woims that fuck with your head.
Not sure how often you get out on the PAN, (clever bastard to own one) but some of the following might be relevant

According to Mr Google, Ye Old Super was 97-98 octane and had a shelf life of over 12 months, longer under cool conditions.
If left for long periods it does not gum/glaze up like Unleaded, i.e. clog up carbies and plugs.

Unleaded has a much shorter shelf life, maybe only 3 months if stored above 30 degrees.
It leaves a gummy deposit as it dries too so if your Pan isn't on the road often it could be the deposits at work and they might take a while to flake off and cause glitches with your carby.  So if sitting for a while, try draining the float bowl, easy on a PAN, just leave it running and turn off the fuel.

I experienced the same issues with fuel in my old bikes till I found a source of Avgas.  As you know Avgas is still leaded.
That's because ''they'' (the Woim breeders) recognised that Unleaded fuel is less stable than leaded, and who wants to be blamed for planes dropping from the skies.
Avgas is 110 RON, and man it gives your engine wings, but I don't believe it's just the octane rating at work.

A good friend who had the sense to collect a lot of bikes including Knuckles, Pans, Flat Heads and Shovels, swears by 91 RON.

As a side Woim, don't forget that AUS and US RON ratings are different, US 95 RON is our 98 RON, US 91 is our 95 etc.

Anyway, he reckons the Harley's larger capacity engines and longer strokes, help atomise the fuel vs bikes like an old Bonnie or CB750 with less capacity for big breaths, don't get a good lungful of fuel mix and therefore run less well.  I know my K2 with those teeny pistons would run fine on 98 RON but if I left it for even 3 days, it wouldn't start without cleaning all 4 plugs.

Same with my 69 Bonnie. When tuning the old 2 cylinder I'd detach one plug lead and tune the engine to run nicely on one cylinder, then do the same for the other side then run a balance check on 2 cylinders afterwards (well that's what I do, others please chime in if you reckon I'm suffering a case of the Woims).  I couldn't follow that procedure with Unleaded 91 nor 98 RON, one side just wouldn't run, got some Avgas and yihar, all good. 

OK so the Avgas has a higher RON rating but I reckon it's more to do with the fact that Leaded fuel (with a different specific gravity to Unleaded) atomises more efficiently through a carburetor than Unleaded (designed for injection systems) and it doesn't leave the nasty deposits, so even a month later the bikes would start first pop, well second kick for the Bonnie.

So where does that leave you Spinsy? well it could be that when you add a fresh batch of fuel, (with all the new tech cleaners) it pushes out the gummy stuff and gives you grief so don't turn off the engine, shut down the gas and let us know if it made a difference.

Then again, maybe it's just the WOIMS.  Get some AVGAS man, er try hanging around airports or race tracks, gokart meeting guys etc might supply the fix you need. 

BYW, please post a pic of the PAN.

Ratbob...you are a classic. I get what you're saying...both in facts and in regards to the woims.

Thanks for the replies boys. Ratbob...are you trying to say I'm in a woimy kind of situation ? I think I just may have a contact who offered to get me some avgas a few years ago. I may just give him a call and see what he can do. Perhaps I should try the 98 first also and see if that makes a difference. I've been using unleaded and it seemed OK. I run that in my other old bikes and they run better on that than the 95 and 98 .... a lot better so yes its a can o woims alright. Is your friend who swears by the 91 ron here or in US ?

Hey Spinsy

Sorry forgot, my mate uses Aust 91 RON in old non EFI bikes. 

Thanks boys. I'll take a pic next day or two and put it up for you. Don't get too excited though its its no wizz bang chromey queen or fab chopper,. just an old jalopy.

Many thanks HH. I've not seen any E fuels for sale yet but it's good know I should avoid it. Cheers

FWIW. I have run both bikes (2003 soft tail deuce, 2014 Ultra) on every type of fuel from unleaded 91, ethanol mix 95 up to premium unleaded 98 without any issues.

I run (mostly) on 95, but not uncommonly fill up with 91 octane that works just fine.
What I found though is by adding a tiny amount of led substitution (Valvemaster Ultra VM750, commonly found in petrol station shelves) each time I fill up, it runs really well on both
I try use a higher octane though, but $ sometimes limits my option
If anyone try this led substitution product you need to pay attention to pings - if that happens you probably dont need it (or you add way to much)

My bike is an -81 and apparently it should be able to handle today's fuel without anything added to it - However,  Ive found that this product actually makes a difference.

The guy I bought my 97 FXDWG (carby) off said he always put 95 in it from when he first bought it almost new in 1998. I have put 91 in it and haven't noticed any difference....

Spinsy, should contact Cow at L A Cycles Sydney, he has had a 65panhead forever and still rides it ( and not just to the pub) he runs it on BP98 but fine tunes it, it is 65 so kick & electric start. But i have kick started it & starts easy ( if you know how to kick start a pan )