Reserve Tank--funny story

schrader7032 · Post by **schrader7032** » Tue Jun 16, 2009 9:41 am

I can tell you there are plenty of us idiots out there! It's happened to more than just you, believe it.

Yes, there are two straws sticking up in the tank, one set on each petcock. The taller straws are considered the "main" tank". There is also a tunnel which runs down the center to get over the back bone, so there can even be two halves of the tank...this affects things more on reserve. The "reserve" straws are a little shorter...sometimes previous owners totally remove the reserve straw so that all of the gas can be consumed...as well as the water and crud at the bottom of the tank. The water and crud is the reason that the tank should be emptied and cleaned on a routine basis.

The standard BMW petcocks have directions for the handles. When the large fob of the handle points to the ground, that's the main tank. The large fob pointing to the sky...that's reserve; and when the fob is parallel to the ground (either pointing forward or backward)...off.

People use all kinds of schemes to manage the fuel in the tank. You can effectively have mulitple reserves depending on how you do this. Me, I run both petcocks on the main tank until she sputters. Then I switch the left (usually) to reserve, leaving the right alone. That's my first reserve. When she sputters again (and this has only happened a few times when I've driven deep into the tank), then I switch the right petcock to reserve...the second reserve.

I play mental games with all this when I'm touring. I keep records of my gas mileage and have back-calculated how many gallons are on the main tank. When the bike sputters the first time, I note the miles driven and divide by this number of gallons in the main tank and compute a MPG. I compare that mentally to previous MPGs. If I'm running normal, it should compare well. If I've been bucking a headwind or doing a lot of city/mountain riding, it might be lower than normal. Whatever it is, I can not compute the number of miles I have remaining on each of my two reserves. My gas mileage logs contain the miles driven when I make the switches on the petcocks. This way I can back-calculate how many gallons are also in each reserve tank.

About that tunnel in the middle of the tank, which can separate the two reserve portions of gas. If you find yourself in the situation where you've gone too deep on the second reserve and have run out of gas, well you haven't really run out of gas. There is still gas below the two shorter straws, assuming the straws are indeed in the tank. You can do a couple of things to get you a little farther down the road. Get off the bike and tilt the bike towards you...some gas will run across the tunnel into the left side...now it will be higher than the straw. Or you can take the tank off and carefully force all the gas on the right side into the left side. You might be able to get another 5-10 miles this way...enough to find a gas station.

Good luck...and happy learning!!

Kurt in S.A.

hargis7556 · Post by **hargis7556** » Thu Jun 18, 2009 1:41 pm

Kurt;

Thanks for you kind comment. I noted you said the tank needs to be cleaned. I have not read anything on how to do this. Is there a more precise way than just taking the tank off and sloshing some additional fuel in the tank and emptying into a container (to be properly disposed of--of course)

schrader7032 · Post by **schrader7032** » Thu Jun 18, 2009 3:31 pm

You're asking me, someone who doesn't regularly clean the tank?

I should be just can't seem to get around to it.

My first approach would be to just do as you say, remove the petcocks and possibly flush with more gas. Button it up and you're good to go. At least the residual water and dirt would be removed.

You can get me anal about it using various chemicals, etc. Snowbum has an article on this:

http://bmwmotorcycletech.info/fuelmiscl.htm

So, somewhere in between is probably good...but don't do as I do, do as I say!!!

Kurt in S.A.

VBMWMO · Post by **VBMWMO** » Mon Feb 15, 2010 2:52 pm

Ok--here is my attempt to show that I can be an idiot at times on my bike.

I took my new (at least new to me) 1971 R75/5 on a 1 hour trip to Williamsburg, VA. It was a beautiful day, sun shining and about 70 degrees.

My bike started up perfectly as i began my fun filled rifing day. I got down to about 12 miles from Williamsburg when my bike began to sputter and stop running.

Well I was a little concerned. I just bought the bike and figured--Great here is the first a a number of events that are going to irritate me about this bike. It is the first BMW I have ever owned--all my other bikes have been Ducati's (and all new).

I stop the bike--tried to start it again and nothing. then I began my checklist of items that could be causing this. I checked the gas tank and there was gas in the tank. Not full or even half by a visual inspection but still some in the tank.

I checked the petcock to make sure fule supply was on (I have been forgetting to turn it on-not being used to them). It was on. After about a 15minute look around, I tried starting the bike again. Wow it cranked right over. I decided to head back towards home just to be safe. Well abouut 10 minutes later the same thing. Ok must be something in the carbs--maybe the flaking inside the tank has lodged in the carbs (I had an Alfa Romeo that did this). the Alfa would set the carb would release the particle and run for a while until I changed the fuel filter. Nothing in the bowls of the carb that concerned me. another 15 minutes later the bike cranked over again.

10 minutes down the road and the same thing--OK fuel starvation but why--where is that damn reserve tank on this bike?? Cant find it--dont understand how it works. Now the bike wont start--battery run down--thank god it has a kick starter!! I am trying everything to restart this engine for the next hour when suddenly I decide to pull the fuel lines from the tank to see if they wer clogged. NO FUEL comming out of the lines--the petcock in in the on position. I blow into the fule line to see if there is an obstruction too free up. blows in ok and air comes back out--what the heck!!!

Well lets see if I adjust the petcock and see if I can get fuel out--I'll be damned when its in the reserve position fule comes out fine. I know that damn mechanic put the petcock in reverse. Ok I can ride with it in the reserve position. THANK GOD FOR A KICK STARTER!!! It cranks right up!!! I get home just fine.

Monday I take the bike over to the shop--I tell the mechanic he put the petcock on wrong--He says NO WAY. then Proceeded to explain to me since the BMW does not have a fuel guage that the tank will run in the on fuel position until it gets below a certian point. At that time the engine will be starved of fuel and you switch to the reserve position on the petcock and the fulw draws from lower in the tank--that is the RESERVE!!! HAHAHAHAHA what an idiot I am--great idea--wich I would have understood how it worked. what an Idiot I am!!!!