Question on petcock use ??

[40427]

Today I went for a short ride , when I got back I discovered that I had only turned on the left side fuel petcock.

The bike ran fine and I did not notice any performance difference. ??

Do most of you turn on both side petcocks all the time, is so why or why not ????


Another subject:
Throttle lock/cruise control ??

My 1985 R80 has the BMW thumb screw throttle lock. For the life of me I cannot set and use it underway. Are there any current options available to replace it.??

I remember I had some sort of a "Vista Cruise" back in the day on an earlier BMW.
Is something like that available in the market today ??

I tried a Throttle Meister and a KAOKO on another bike, but due to some right hand damage I cannot manipulate either one of those types very easily.

Thanks, Doug

 

[20774]

You should have a cross over fuel hose on the output line to each carb. This lets one petcock provide gas to both carbs...helps to ensure sufficient flow in all situations. Also, because the tank has a saddle in the middle, at low tank levels, you'll have pockets of gas on either side. Only one petcock can drain each saddle, so you really need the cross over at that point.

Quite a few ways to run the petcocks...I'm sure you'll hear a few. I run both petcocks in the "ON" position to start with. When I hit the reserve mileage and the bike shudders, I usually reach down with my left hand (because the right is working the throttle to keep me going!) and turn it to reserve. I then consider if I want to fill with gas or not. If and when the left petcock hits reserve, then I have to be ready to reach down for the right petcock. At that point, I really better be thinking and heading for gas. Use your gas mileage and back calculate how much gas it takes to burn to the first reserve (this is the MAIN tank), and how much gas is in each saddle. It may come in handy when you're somewhere between Hoover Dam and Kingman with a quarterly headwind wondering if you're going to make it!! And you didn't talk to your wingman...and he's in the same boat!! On a wing and gas fumes...

As for throttle locks, that screw is really for just a couple of purposes IMO. One, used to hold the throttle locked when doing carb synching. Two, for adjusting the drag on the throttle which would let you remove your hand for a split second and not have the throttle snap back to idle.

But there are some cruise controls out there. Some are just small add-ons that let you use the heel of your hand to stabilize the throttle while you flex your fingers. Crampbuster is one name. There are others that actually clamp on the throttle tube and prevent it from turning. Rider's Wearhouse has a variety of things to offer:

http://www.aerostich.com/catalogsea...e+lock+cruse+control&dir=desc&order=relevance

 

[krpreston]

Petcock use

I only turn on one petcock as one provides way more than enough gasoline to run the engine and moreover because if I hit reserve on that side I still have a significant amount of gas left on the other side and more options for filling up. If you open both petcocks and hence simultaneously run both sides down to reserve, you don't have much left. My handbook suggests about 25 miles left at that point. Fortunately, I've never had to test that.

 

[PGlaves]

One on, the other on, or both on flows gas.

 

[James.A]

I like to run only the left side petcock on main. Then, when the motor stumbles I turn the left side petcock to reserve and start thinking about finding fuel. If the left side goes completely dry, I tap the right side on reserve and get serious about finding fuel.

About the throttle screw, I'm not sure it is a good idea to lock the throttle open. I have seen a few bikes with alternate part in the hole for the throttle screw that is like threaded shaft with a lever riveted in the end that protrudes so you could turn with your thumb.

 

[Woodgrain]

It has been mentioned in the past, and is probably conjecture, that the R100 models like their fuel, so it's preferable to have both petcocks "on" to keep those carbs fed.

Woodgrain

 

[krpreston]

It has been mentioned in the past, and is probably conjecture, that the R100 models like their fuel, so it's preferable to have both petcocks "on" to keep those carbs fed.

Woodgrain

This isn't conjecture; it's pure nonsense! Compare the size of the ports in the petcock to the size of the carburetor jets and try to imagine how a petcock could starve two carbs.

 

[20774]

Check your fuel flow...a note I saved from Tom Cutter says that the flow rate should be a minimum of 350cc/min to each carb. Snowbum says that a petcock should file a cup in a minute as a minimum flow rate, or ~235cc/min.

One petcock should do that. If not, then you have flow problems. Eventually, when you get down to that "last" reserve, you're flowing on one petcock...you really need the flow at that time.

BTW...a "trick" when you really, really run out of gas... Take the tank off and slowly tilt it to one side of the other. That combines the bit of gas below the lowest petcock straw on both sides into enough to be above the straw on that one side. Might get you another 5-10 miles. Better than walking!!

 

[40427]

Oh my !!
What have I started ??

Obviously I had a senior moment today, I always fly with two petcocks locked and loaded to deliver fuel

I guess in my dotage I need to develop a pre-flight check list and tape it to the inside of my helmet.
Now if I could only remember where I put my helmet.

Feel like an idiot.
But at least I know the left petcock is functioning correctly. Maybe I will try it on the right side tomorrow.
Probably need to take them apart and rebuild them anyway, seems like I am rebuilding this bike from one end to the other one piece at a time.

 

[beemeruss]

Fuel management

As in flying,but to a far lesser degree,airhead fuel management on a long cruise is important.My technique on a new- to- me airhead is to run on the right petcock until the engine stumbles.Running on the right side allows the use of throttle while using the left hand to engage the left one as Kurt mentioned.I then fuel up as soon as possible to determine how much fuel main #1 had used.The next time I run until main #2 (the fuel on the left below the saddle) is depleted and repeat the drill to know how much fuel #2 holds.Simple math then determines how much fuel remains between the 2 reserves.My '76 R90/6 went 9 miles on each before total fuel exhaustion one half mile to the gas station.I guess that I drew the short straw(s)!
On the throttle lock situation I use the thumbscrew with enough tension to allow me to scratch my nose before the return springs take over.I use a velcro- held cramp buster as a wrist rest to wiggle my carpal tunnel fingers for longer periods.My R100 RS came without said thumbscrew but when I looked carefully where one should be I noticed a clear plastic plug occupying the drilled and tapped hole .The one from the R90 fit perfectly.Russ









.

 

[40427]

I have been using a Throttle Rocker for a couple of years now and it does help.

Just on my trip to Daytona my right hand and thumb began to complain more than usual. Just old age and infirmity I suspect.

 

[JT_R1200RT]

I see now the cross over is under the air box, I didn't notice this before.

-JT

 

[22600]

You choose

One on, the other on, or both on flows gas.

Your question "Do most of you turn on both side petcocks all the time, is so why or why not ???? "


As you can see there are many different opinions on this subject. It doesn't really matter. Paul has it right on his quote also. My OPINION and what I do is leave both on then fill up when my butt gets tired, which could be anywhere from 100 to 200 miles. Ya'll young guys need to get a spare tank.

 

[44006]

If the bike sits around a lot and or makes only short trips once in a while it is a good Idea to occasionally run both sides on reserve for a short trip you know you will not run out of gas.

Reason for this is to drain out the crud that collects in the saddles from the contaminated with alcohol gas now being sold in most of the US

If you always run on normal on position and never get to reserve you can collect quite a bit of milky crap in the saddles that will kill your engine when you need it the most - the panic moment in traffic when the engine stumbles and you need to accelerate - you switch to reserve and it dies instead of comming back on

 

[osbornk]

I've had my R80RT a little over 13 years. I have always opened only one petcock. I've never had a problem and I have 3 reserves. When the tank runs dry on one petcock, I open the other, when that runs dry, I put one side on reserve followed by putting the other side on reserve. You're never going to have stale fuel because it sloshes around as the bike is used and when fuel is added.

 

[lonerider]

Riding with one petcock open

I never tried to figure required cc/min but I have ridden with one petcock closed.
I can say for certain that years ago my R75/5 would run fine under normal conditions with only one petcock open.
However when attempting full throttle acceleration from a stop it would starve (miss, stumble, cut-out) for fuel before 70mph. When running on one petcock: The fuel has a short straight path to one carburetor and a longer path with two 90 degree turns to the other.
While I normally ran with both petcocks open, I would go to reserve one at a time so as not to forget.
Run them as you choose. The only wrong way is to put both on reserve and then run out of fuel.
Happy Trails
Lonerider

 

[airraceaddict]

My experience says........

Run with both on. When you need to switch to reserve, switch to reserve on the left for obvious reasons, once you are stable, switch the right to reserve and switch the left to off. If you need the second reserve, you will be able to switch without taking your hand off the throttle at maybe the most inopportune time. My 78 R100RS will go approximately 20 miles per side.
The "trick" mentioned earlier to roll the gas from one side to the other to get it over the stanpipe has definitely kept me from walking a couple of times I will take the time from now on to stop and fill up as soon as I can before I have to switch to reserve 2.

 

[ISAMEMON]

Run with both on. When you need to switch to reserve, switch to reserve on the left for obvious reasons, once you are stable, switch the right to reserve and switch the left to off. If you need the second reserve, you will be able to switch without taking your hand off the throttle at maybe the most inopportune time. My 78 R100RS will go approximately 20 miles per side.
The "trick" mentioned earlier to roll the gas from one side to the other to get it over the stanpipe has definitely kept me from walking a couple of times I will take the time from now on to stop and fill up as soon as I can before I have to switch to reserve 2.

why is it "obvious" to start on the left ?

 

[20774]

why is it "obvious" to start on the left ?

I'm guessing because it's the natural hand to use when the right hand is busy working the throttle. Unless you happen to be mid-clutch, in which case things will get real fun!

 

[PGlaves]

Turn fuel on. Left, right, or both. Start engine. Ride. Turn fuel off.

This does not need to be over thought. It is neither a religion nor a fetish.

What ought to be talked about is the damage possible when you leave the fuel on, it runs past a bad needle/seat, flows into a cylinder and gets in the oil. Hydrostatic lock, a bent rod, and bearing damage. Those are the lessons of petcocks.