Boxerworks.com

Rob said "You will want to drain the tank so that you can drop both petcocks and check for debris and make sure that the screens that go over the outlet tubes are in place and looking good."
+1. Good idea!

Horizontal (either direction) is OFF
Down is ON
Up is RESERVE
couldn't be simpler
You can empty one reserve at a time.
On a stock system, if everything is flowing properly, either tap will feed both carbs simultaneously without concern.

It's a good idea to slowly rotate each fuel tap lever a few full turns occasionally so the gas can lubricate their internal seal(s) and keep them working smoothly. If they are really stiff, wiggle them back and forth until they can freely be rotated 360 degrees.

I would strongly recommend checking your float bowls for water and debris immediately,
and then again at regular (monthly?) intervals.

Wow! I wasn't expecting so many responses!

Rob wrote: ↑Wed Apr 21, 2021 2:38 pm You probably had one petcock on, and one off, but the crossover wasn't sufficient to feed both carburetors, which probably need some cleaning, no doubt.

Absolutely was running one on one off. I figure that's why at higher load/RPM, the fuel flow from a single petcock wasn't sufficient. It's also equally likely that perhaps it's in need of cleaning and/or the tubing may be semi-clogged?

Rob wrote: ↑Wed Apr 21, 2021 2:38 pm
I also recommend you empty the fuel tank and flush it, if you haven't already. Get any water out that might be in there.

Yep. This is on the agenda for next week I hope.

Rob wrote: ↑Wed Apr 21, 2021 2:38 pm
The stock charging system is just adequate on a good day. If it has a lead-acid battery, consider upgrading to a sealed unit. I'm sure the guys can recommend a current model. I don't remember which one I had (black w/orange top). I bought it, and never bought another until the day I parted out the bike.

It's got an AGM sealed in it now. Bought it about a month ago.

Steve in Golden wrote: ↑Wed Apr 21, 2021 3:29 pm Occam's razor strikes again!

Welcome to the forum kmisterk!

Photos, we need photos of the bike pls

Haha, you're not wrong. The simplest solution often is the correct solution. And thank you! I am super happy I found this place. Photos will absolutely be coming soon, as soon as I manage to remember to take pictures of it Like, good ones. Every time I say that I want to, I get to the bike, and all I wanna do is ride it lol. C'est la vie. SOon, though, I promise!

melville wrote: ↑Wed Apr 21, 2021 3:31 pm Welcome to the board! So happy for simple solutions.

Thank you! And yes, thank god! I was like, in the process of mentally preparing for a weekend discovery-and-repair session! Maybe next year

Rob wrote: ↑Thu Apr 22, 2021 9:31 am Petcocks can be rebuilt.

...

You will want to drain the tank so that you can drop both petcocks and check for debris and make sure that the screens that go over the outlet tubes are in place and looking good.

Noted! Based on what I've seen so far, and from what the local shop mentioned when I took it to get new tires (yeah, I'll do it myself next time, don't you worry), the bike has been exceedingly well-maintained. However, this is easy maintenance, considering how easy it is to actually get the tank off.

gspd wrote: ↑Thu Apr 22, 2021 12:38 pm
On a stock system, if everything is flowing properly, either tap will feed both carbs simultaneously without concern.

And for the most part, the bike worked fine under light load at low RPM's. When the gas needed to flow, though, such as at higher RPM's, it started to bog.

gspd wrote: ↑Thu Apr 22, 2021 12:38 pm
It's a good idea to slowly rotate each fuel tap lever a few full turns occasionally so the gas can lubricate their internal seal(s) and keep them working smoothly. If they are really stiff, wiggle them back and forth until they can freely be rotated 360 degrees.

I would strongly recommend checking your float bowls for water and debris immediately,
and then again at regular (monthly?) intervals.

Good tip about lubing it up with the rotation trick. Definitely an easy maintenance action. Why the worry about the Float Bowls? Does running off of a single petcock cause any different behavior than both open, or is it just generally good practice to check them for water/debris anyway? It has an in-line fuel filter on both sides, so I'd wager it'd be quite difficult for large debree to get in there, unless through the air filter and passing in through the carb, somehow?

Not a terrible idea, in any case, and I most certainly will take the the time soon to check out the float bowls in pursuit of good maintenance practice.

Two schools on the inline filters. I chose not to use them. My petcock was the type that had the large screen inside the tank, and a smaller screen at the exit nipple of the petcock.

There have been many arguments over restriction of flow, that sort of thing.

Rob wrote: ↑Sat Apr 24, 2021 4:31 pm Two schools on the inline filters. I chose not to use them. My petcock was the type that had the large screen inside the tank, and a smaller screen at the exit nipple of the petcock.

There have been many arguments over restriction of flow, that sort of thing.

+1

Add on after-market fuel filters are redundant and unsightly (just plain ugly) and they have been known to impede fuel flow at high speeds.
They give a false sense of security and do not prevent water and crap from accumulating in the gas tank.
Just clean out the water and crap from your tank filters every decade or two, their mesh is as fine as most in-line filters.

Rob wrote: ↑Sat Apr 24, 2021 4:31 pm Two schools on the inline filters. I chose not to use them. My petcock was the type that had the large screen inside the tank, and a smaller screen at the exit nipple of the petcock.

There have been many arguments over restriction of flow, that sort of thing.

Oh, interesting! So realistically, I could just replace the tubing on both ends with longer tubes and forgo a filter altogether, so long as I make sure to rinse/clean out the screens on the petcocks?

Noted. I'll have to add that to the list of modifications I plan to make.

gspd wrote: ↑Sat Apr 24, 2021 5:34 pm
+1

Add on after-market fuel filters are redundant and unsightly (just plain ugly) and they have been known to impede fuel flow at high speeds.
They give a false sense of security and do not prevent water and crap from accumulating in the gas tank.
Just clean out the water and crap from your tank filters every decade or two, their mesh is as fine as most in-line filters.

Thanks for the confirmation and second opinion! I did feel like the inline fuel filters looked odd and out-of-place.

kmisterk asked :" So realistically, I could just replace the tubing on both ends with longer tubes and forgo a filter altogether, so long as I make sure to rinse/clean out the screens on the petcocks? "

I would.
If you replace the gas lines, don't use the commonly available 1/4" hose from the corner auto-parts place.
It doesn't fit firmly on your BMW fittings (may require unsightly hose clamps, yuck!), and the larger OD prevents it from fitting through the airbox (cross-pipe).
You need 7mm I.D. (metric) fuel hose.
It comes in cloth covered type (pre 1985-ish?) or plain rubber type.
I like the plain rubber type, seems to age better cosmetically (doesn't turn grey and get frayed ends)
Both are available from BMW (by the meter) or most places that fix old VW's and such.

gspd wrote: ↑Sat Apr 24, 2021 5:34 pm
Just clean out the water and crap from your tank filters every decade or two, their mesh is as fine as most in-line filters.

I bought my R65 new in 1980. Back then, where I live, we put our bikes up for 3-4 months during the winter.
I did not like the idea of fuel stabilizers (I'm not a chemist for nothing!), so, annually, I would drain my fuel system and leave the tank open until it was dry, then close it up for the winter. I always had the original liner.

On another subject/warning,
if you remove the airbox to replace the fuel hose, you will see a large (13mm?) fastener on the top of the gearbox. LEAVE IT ALONE! Unless you are planning to rebuild your box, of course... (leave it alone)

Can't speak for the four speed box as shown but on the five speed box, you can remove the 13mm bolt as much as you like. it simply threads into the top of the casting and holds the airbox half casting retainers (early camshell airbox) or lower airbox casting (later rectangular airboxes) in place. In fact, with the later airbox, you have to remove the bolt in order to take off the airbox. The fixing to leave alone is the crosshead screw which is also in the top of the box. If you remove this, it will release a sheet steel oil channel which will drop into the gearbox mechanism and, should you try to use the machine before you have dismanlted the box to relocate it, cause horrendous damage.

Rob

Thank you for the clarification, Rob.