Why not just run on Reserve and calculate with trip odometer?

[Guest]

I was watching a youtube video on carb cleaning by one of our members when he recommended not messing with the petcock too much for fear of wear and leaks. He recommended leaving it on Reserve. I use the trip odometer anyway to calculate gas with a reserve calculated as well.

Any problems with using Reserve and calculating rather than on Run and have it stumble while switching to Reserve?

1980 GS850G

[tkent02]

I was watching a youtube video on carb cleaning by one of our members when he recommended not messing with the petcock too much for fear of wear and leaks. He recommended leaving it on Reserve. I use the trip odometer anyway to calculate gas with a reserve calculated as well.

Any problems with using Reserve and calculating rather than on Run and have it stumble while switching to Reserve?

1980 GS850G

Reserve sucks fuel from the very bottom of the tank, where all the loose crap ends up. Do you really want to go there all the time?

If your petcock fails it's because of old age and neglect. Clean it out inside once every five or ten years, replace it every 30 years or so and ride happy.

By the way your calculations don't mean much if you spring a leak, leave the choke on, someone borrows some gas, you drop the bike and spill some out, or any number of other things happen that can reduce fuel mileage.

[mmattockx]

By the way your calculations don't mean much if you spring a leak, leave the choke on, someone borrows some gas, you drop the bike and spill some out, or any number of other things happen that can reduce fuel mileage.

Or simply get some clear road and spend some time with the throttle twisted open farther than usual. Spirited riding alone can drop mileage by 30% or more compared to an easy cruise. I agree, ride on the main setting and switch to reserve when you need it. That leaves a known amount of fuel to get to the next station or home or wherever.


Mark

[posplayr]

What is wrong with calculating fuel level based on mileage? Trying to be smart but not smart enough. Yes fuel consumption can vary for a variety of reasons mostly not accounted for in the op's calculations


You were smart enough to ask without having to learn by hard knocks

[Steve]

In the words of Harry Callahan, "How lucky do you feel, punk?"

The mileage on my wife's bike has ranged from 28 (75 mph into a 20 mph headwind) to 59 mpg (50-60 mph in the hills of Kentucky) on the same trip. She usually flips the petcock to REServe at about 140 miles, but let me know she did it at 85 miles. If the petcock had already been on REServe, we (I) would have been pushing, and THAT ain't gonna happen.

.

[UncleMike]

If you leave your petcock on RES, you're operating on gravity not vacuum. Plus, I'd guess that regular use of your petcock would prevent it from leaking rather than the other way around. Gasoline is a lubricant.

[tkent02]

If you leave your petcock on RES, you're operating on gravity not vacuum.

Not true, RES works exactly the same as ON except for feeding off the bottom of the tank. Res uses the same vacuum diaphragm, the same on off valve.

You are right about using it being good for it.

[hampshirehog]

It's pretty much what those of us with the 1980 tap do all the time (there's no reserve). Ask everyone with one of those taps if they would prefer having a reserve back up and guess what the reply would be.

[Steve]

If you leave your petcock on RES, you're operating on gravity not vacuum.

I was puzzled by this, too.

No matter WHAT position you use, you are always "operating on gravity".

The only thing that "vacuum" has to do with the process is to turn on the tap.

.

[Steve]

It's pretty much what those of us with the 1980 tap do all the time (there's no reserve). Ask everyone with one of those taps if they would prefer having a reserve back up and guess what the reply would be.

Fortunately, not all of the '80 bikes were 'blessed' with that stupid piece of "engineering".

The 850G and 1000G have proper petcocks with levers.

There might be others, be we happen to have one of each of these in the stable.

.

[UncleMike]

I was puzzled by this, too.

No matter WHAT position you use, you are always "operating on gravity".

The only thing that "vacuum" has to do with the process is to turn on the tap.

.

Then why doesn't gas flow freely from the petcock when it's set to ON. On my petcock, when it's set to ON the gas only flows when the engine is running and pulling vacuum. When it's set to PRI it just flows freely, no need for vacumm.

I was under the impression that the same was true for RES, but I guess I'm mistaken.

[Steve]

Go back, read my last line.

The only thing that "vacuum" has to do with the process is to turn on the tap.

Yes, you need vacuum to enable flow in the ON and RES positions. The PRI position does not need vacuum, unless you have the "dreaded '80 petcock".
If you are 'blessed' with one of those, it takes a brief 'puff' of vacuum to get fuel flowing, then it will continue until you move the selector or the tank runs dry.

.

[tkent02]

PRI needs no vacuum on most petcocks, RES does. It's just like ON but from the bottom of the tank..

When you turn off the engine the flow should stop in reserve, just like in on.

PRI will flow until the tank is empty.

[UncleMike]

PRI needs no vacuum on most petcocks, RES does. It's just like ON but from the bottom of the tank..

When you turn off the engine the flow should stop in reserve, just like in on.

PRI will flow until the tank is empty.

I'm guessing this bit of misinformation is due to a crappy old petcock and tank I used to use as my fuel container when balancing carbs. Petcock wouldn't go to PRI but I could set it to RES, and the fuel would flow freely. Probably just a worn seal?

[BigD_83]

I'm guessing this bit of misinformation is due to a crappy old petcock and tank I used to use as my fuel container when balancing carbs. Petcock wouldn't go to PRI but I could set it to RES, and the fuel would flow freely. Probably just a worn seal?

or a misbuilt petcock...