Because this subject was brought up, while conversing with another forum member, I wanted to explain why the rumor exists, that it is bad for your bike, to run the petcock in the "Reserve" postion. This is just to clarify things, for any guys and gals out there who just might not have a clear view of how it works.

It is not bad to run in "Reserve", but it can be bad... here's why:

What divides the fuel tank into a primary capacity, and a reserve capacity, has nothing to do with the tank itself, but merely the petcock.
When the petcock is in the "On" position, fuel is drawn from the top of the tube, which stands vertically in the tank, from the bottom, when the petcock is installed - this is circled in green, in the picture below. Bear in mind, these are NOT F2 petcocks pictured - these are just used to illustrate the concepts.




When the fuel level falls below the top of this tube, the bowls dry up, and you begin to experience the stuttering associated with fuel starvation, then you switch to reserve. When you switch to reserve, a valve rotates to where fuel is then drawn from a hole in the lower section of the petcock - that area is circled in red.

This is a picture of a petcock from an old Ural bike, and you can clearly see the separate hole that continues to allow fuel to flow, to a much lower level in the tank.



The key to this functioning properly, without the issue of drawing in dirt, and other sediment, when in reserve, is the presence of the screen, that the screen is not torn or damaged in some way, AND that the sealing washer is in place, and is also undamaged.
Here's the first petcock again, with the screen in place:



As you can see from the construction of the screen, even if the sediment particles are small enough to permeate the screen, that can no longer happen below a certain level, and it's at the bottom of your tank that sediment will most likely exist, which is why they are made this way.

Both of my fuel tanks are squeaky clean, with no visible "junk" in them at all, but in a case where a tank does obviously have things floating around and/or settled at the bottom, and there is no screen present, that is in proper working order, you should avoid using reserve, until this can be addressed.

So, the reason a lot of guys just associate the "Reserve" setting, with possibly contaminating their carbs with sediment, stems from learning of situations where there was no screen there, or it was faulty, and not doing its job.

The concepts are nothing complexed, but like anything else, you don't know it until you learn it! Hopefully this will be helpful to some.

 

Interesting post. I've never taken apart the petcock on my F2 and I always imagined the 'screen' to be a little disc somewhere in the actual fuel line. It's good to have a better understanding of how it works in case I have to deal with any problems in that area.

 

I was unaware I was running my F2 on reserve when I first got it. Before that, it ran absolutely perfectly from zero, all the way up the tach. Then the carbs got so clogged, I could barely start it. Tried tanks and tanks of cleaner. Trying to ride it out. Got carbs cleaned now is fine. Fuel screen AND tank were very clean, but something from the bottom must have got in there. It was such a pain in the A$$, that I will NEVER. EVER. Run on reserve unless I am in a desparate situation. To me, it's simple. If you have anything on the bottom of tank, there's always the chance it can get into your carbs, period. And tanks never all of the sudden get cleaner. Not tanking any chances.

 

Great write up!! This is something that should have been addressed for some time

 

I guess the O' Ring could have issues, but I don't know honestly. Everything else is in such good condition, I can only assume.

 

I get where you're coming from, but if you did suddenly get some clogging in your carbs, and you can surely tie it to times when you were in the reserve position, I would yank the tank and pull the petcock, and give it a thorough examination, and just have one of those o-rings on hand, so you can replace it when you go back together, in case it is bad (O-ring is $2, screen is $15)

Like I said, you shouldn't have any issues with reserve, if all of these components are doing their job... with both of my F2s, I don't fill up until I have to switch to reserve (well, except when I'm on the track! ), so that I'm keeping mostly newer fuel at all times, and I have never had an issue with any junk being introduced into the fuel bowls.
For the record, I'm not running an additional inline filter on either bike, but I don't think there's anything wrong with that - if there were more room to splice something in, I might have done it before, just as an extra layer of defense.

 

"Tanking" any chances... you're a funny guy!

 

Did I write that!? Haha that is funny. Didn't realize my misspelling until now

 

I'll take your advice and look into getting an O-ring and screen. Funny thing is that about a week ago, I accidentally ran the bike on reserve and didn't notice until I got home. Did about 15-20 miles. And it didn't have any noticeable effect. Sigh. Funny thing though is that for most all vehicles (used) i've ever owned, most major things that go wrong with them, happens within the first few weeks. This happened within the first couple.