It could be that your fuel line isnt routed correctly and is getting pinched off.

Quote from: RPM - Robert on February 24, 2026, 10:35:03 AMCorrect on the 86/87 model it should not flow any fuel until vacuum is applied. If it is flowing fuel the petcock is bad.

The 84-85 has a prime function which will flow fuel when the selector switch is in the prime position but in the on position it should not flow fuel until vacuum is applied.

So looks like I still have some issues with gas supply.
Petcock does not leak so I assume membrane is still good/or not??? However, starving for fuel - means issue with vacuum??? Vacuum hose looks good so solenoid doesn't work???

Thanks

Thanks

I use 2k epoxy for metal and plastic. Done.
But, extremely care if you spill a drop of brake fluid onto those plastics, it will crack in a 20 seconds, you will have plenty plastic to glue. This kind of plastic is disaster to save. 

We found new method how to put new diaphragms onto floaters!
Do not use any sharp tools to avoid cuts.
Just find proper strong rope with less than 1mm diameter.
Put the new diaphragm carefully onto place, adjust direction for groove, dip the rope into oil, press exactly on the edge and go all the way around  for few times. Just make sure once is done that is all the way inside (look for the membrane overall look assembly).

If someone needs more, i can send a photo how to do it exactly.

Best regards

Thanks Alan!

I never had any issue running 87, or even 85 octane in my 1200.
I rarely ever ran 91 in it. Never noticed any difference in the way it ran with regular fuel or higher octane fuel, even in the summertime.
5600-feet here in Aurora.
Compression is a bunch lower at altitude, so you can run lower octane fuels.

I always stored it with "Ethanol-Free" fuel though........Makes a difference.

Hey John, Dynojet has their own proprietary jet sizes so disregard my Mikuni jet sizes.

I thought you had stock jetting. I think your Dynojet jetting should be fine.

Storing your bike with 87 octane ethanol free gas is fine. Short rides are fine.

On a hot summer day @ 5,500' the air density in Lakewood is low, meaning air flow for our engine cooling cooling is less, so in my opinion, I would avoid riding in summer stop and go traffic with 87 octane gas. Perhaps I'm being overly cautious.
Other folks can chime in....

If you want to do a plug reading, be sure to disconnect and cap off, the vacuum advance, pop in fresh plugs then ride to get the plugs to the proper color.

With the vacuum advance connected, you will find your plugs are white.... not an accurate color reading.

More info on the vacuum advance: https://fjowners.com/index.php?topic=11690.0

Cheers Pat

LOL it was quite the sobering dream!

Hi Pat,

After I bought the bike last spring I overhauled the carbs and installed a dynojet stage 3 Kit with 120 main jets and 144 pilot jets then tuned the carbs accordingly. Bike runs good as far as I can tell but don't have anything to compare it to. I havent checked plug color yet...

Would you suggest reverting to your recommendations?

Regarding octane I was running 91 on hot days and never had any pinging and wasnt sure if E free 87 was ok.

I'll stay tuned if anyone has a cure but my bike rides fine