Fuel Reserve

[great white]

Seems to me a simple experiment could sort it out.

Drain the tank, set up a gravity feed like what I use for carb synch. Simulate the fuel sender showing empty with the RES off (ie normal position).

If the bike stumbles on a straight gravity feed and the gauge showing empty (or near it) it would seem the bike is pulling ignition. If it keeps chugging right along, then it's manipulating the fuel pump.

Would be easy enough when doing a carb sync to perform that simple little test.

I might check it out myself when I do my 4 gas and carb balance for this season....more for the sake of my own curiosity as anything else....

[Pat Conlon]

My response is in green
A few questions based on your theory.

1) So, there is a "quick fill" function of the fuel pump.

How does that work?
Regulated voltage to the pump?
No, just the regular fill rate

2) Are you implying the pilot jet circuit is still in play at 60 mph?
Sure,  Speed has nothing to do with it, throttle position does. At 1/4 throttle opening the pilots are flowing. When a rider runs out of fuel the bike starts to stumble. The rider naturally opens the throttle further and the bike momentarily recovers as it draws fuel from the mains (feeding the needle jets) this continues until the fuel level in the bowls drop below the level of the mains, then the engine stalls.


If that is not the case, how does the engine start to sputter when the pilot circuit is not in use?

3) finally, since the only function is the fuel pump being shut down how do you explain the function of the 86-87 reserve system.
My experience (that supports my theory) is with the fuel pump FJ's. I do not have, or ever had an '86/87 FJ so I can only guess...Ok so we are back to the non fuel pump '86/87 with a reserve switch. Obviously not a fuel pump interrupt.
***Tell me the purpose of the wires going to the petcock on the '86/87?***
Ignition interrupt? Not likely.
I would like to experiment with a '86/87 petcock, see what happens to the flow

[Pat Conlon]

Seems to me a simple experiment could sort it out.

Drain the tank, set up a gravity feed like what I use for carb synch. Simulate the fuel sender showing empty with the RES off (ie normal position).

If the bike stumbles on a straight gravity feed and the gauge showing empty (or near it) it would seem the bike is pulling ignition. If it keeps chugging right along, then it's manipulating the fuel pump.

Would be easy enough when doing a carb sync to perform that simple little test.

I might check it out myself when I do my 4 gas and carb balance for this season....more for the sake of my own curiosity as anything else....

Good idea   Certainly safer than what I went through.....

[Mike Ramos]

Gentlemen,

In response to Great White here is something along the lines you suggest - but in actual riding.  It may not be conclusive and I do not claim it is, however it is based on repeated experiences...  [I trust dear Mr. Cass is not offended...]  Anyways, below is from a post from September, 2013...!  Keep smiling...

"Howdy everyone,

Well, while Mr. Conlon's statement implies the fuel pump is involved in the operation of the reserve switch it does not disprove that the CDI unit is not canceling out the ignition as well.  

If I may state my experience, which while it may not be conclusive to this discussion, it may have some merit.  

I have an auxiliary fuel tank that I have plumbed through a fuel transfer valve which in turn leads to the fuel pump.  

As I run the auxiliary tank dry, without involving the CDI unit or fuel pump shut off in any way, the engine stumbles and misses, prompting me to transfer to the main tank and there is a delay before the engine is up and running again.

Now, running on the main tank as I go on reserve the engine again begins to miss but it seems to be just that, an engine misfiring, not running out of fuel, AND it is noticeably different from when the auxiliary tank runs dry.  And when switched to the reserve (on the main tank) and the engine resumes its' normal cadence, it is noticeably different and quicker than when the engine has actually run out of fuel.

So for what it is worth, that is my experience with the reserve switch...."

[Mark Olson]

I am glad I have an 86 .

with all this information on the fuel pump models cutting out the ign. I thought this was solved years ago and somebody figured out it just cuts 1 of the coils and runs on the other till you click onto reserve. Basically running  on 2 cylinders .

[Cass]

I am so sorry for opening this can of worms and so glad that I put that I was new to the forum at the beginning of my question.
Not being aware of the previous history of this subject I apologies to Mr Ramos for  being short with him.
Having said that I did try and search the forum on details of the reserve switch but came up blank so I blame the forum search engine for not being any good.
Thanks for all your replies and I will keep an eye on the trip rather than rely on the switch.

[Mark Olson]

yeah , just like the old days before fuel guages on bikes... wow how spoiled we are now.

I remember just opening the gas cap and looking in as you rock the bike side to side and telling your buddies " ya , I can go another 50 miles".

Final note from me on the fuel reserve is that it works on the FM electrical principal ... Fuck'in Magic .

[Rich Pleines]

In my opinion,with a few notable exceptions, this has been a very informative, educational thread on the reserve switch. Lots of knowledgeable exchange of opinions and theory's. There is apparently still a lot of meat left on this bone. Maybe it is time for another oil thread. 

[ZOA NOM]

Oh Jesus... this again?  


edit: never mind... I remember Randy was right.

[Flynt]

it works on the FM electrical principal ... Fuck'in Magic .

Ha...  and the magic smoke got out of mine I guess since it doesn't work at all.

I've never bothered to figure out why, but Wiz only runs the fuel pump with the switch in reserve.  If you switch to normal, it also runs fine until the fuel bowls start to run dry and then it sputters and gets worse until it dies.  Switching back to reserve quickly, but not immediately fixes the problem as the bowls refill...  this supports the thought it just interrupts fuel pump power when low fuel light comes on (Wiz was ABS, so it has no low fuel light).

My $0.02...

Frank

[ribbert]

What a way to welcome in the weekend with the resurfacing of this old chestnut.

Let me make it very clear. How the reserve switch functions is not and never has been in doubt. The only issue has ever been who understands it and who doesn't.

How do you like your proof served up...

Anecdotal
professional
Empirical
Scientific

It has been proven every which way.

FFS, this is kindergarten level diagnostics. I know this is an owner's forum and not a mechanic's forum but proving it for yourself for those who have even basic mechanical knowledge is simple. This idea that it is an ongoing mystery is absolute rubbish.

Some years back when this was discussed at length, I conducted some tests, not for my benefit but to demonstrate beyond doubt how it worked. The results were irrefutable, until Randy called into doubt my professional credentials and suggested that my findings were not credible unless supported by video. Errr, that would be a video showing a test light on......then off......then on......  The suggestion that I couldn't tell the difference or that I was misrepresenting the facts beggars belief.



Rich Pleinnes- there is no meat left on the bone. This is not the space shuttle, it is the reserve switch on a motorbike. Figuring out how it worked was instant, proving it took 5 mins (and has been previously posted)

Mark Olsen - the symptoms of electrical vs fuel interuption cannot be mistaken one for the other. Especially a bike cutting to 2 cylinders as opposed to running out of fuel. There is a chasm between the two. The idea you mention that it cuts to 2 cylinders was not the resolution but the myth that was dispelled. I see no point in being glad you don't have a fuel pump, it is the only way to get proper filtration and in use, are trouble free. Petcocks seem to give far more grief here than pumps.

Mike Ramos - I don't know where your reserve fuel tank is but presumably it is further away from the pump than the bike tank. Of course it's going to take longer to draw fuel from it. The time it takes is relative to the distance it has to travel and the amount of fuel it has to move).

Great White - the test has been done a number of ways. The simplest one being putting a test light on the pump when the main tank starts to splutter. Tip the bike to left so that what little fuel remains flows away from the sender unit and the light goes out. Stand the bike upright (or to the right} it comes back on. With it tilted to the left and the test light off, move the switch to "RES" and the light will instantly come on. Or, as Pat described, simply pull over when the bike stops running on the main tank, with the ignition on and switch to RES and you can hear the pump spring into action.

Randy - there is no "quick fill" function and there is no relevance to earlier non fuel pump models. The restoration of normal power is NOT instant when you flick the switch, it takes a number of seconds to regain normal operation. The time depends of the how long you have let it stumble before switching it over. If you are tuned into your bike and pick it up at the very subtle onset, it is very quick, it you wait until the thing will barely run, it takes longer after switching over (more fuel needed to fill the bowls) As for the manual not mentioning the switch in the circuit, as you know, workshop manuals have many errors and omissions. However, what you have in front in you is what it is.

Pat Conlon - you are right, it starts out so subtly you can barely pick it and gets progressively worse until it eventually dies, switching to reserve if left until this stage takes longer to restore power.

Randy (again) much of you argument seems to stem from the belief that power is restored "instantly" when switched to reserve, it's not. The longer you leave it stumbling before switching over, the longer it takes to run clean again.
I don't know whether you ride this model yourself and if so how often you run it to reserve, but the restoration of power is definitely not instant.

Zoa - maybe you could contribute your own findings on this subject.

Frank - makes sense.

The bottom line is, there is no mistaking an engine running out of fuel with one that is running out of spark.

Great stuff guys, just like the old days!

IMO

Noel

[JOMPPA10]

I  hope you undestand my bad english : reserve switch work that vay (AND IT VORKS OPPOSITE WAY BY SWITCH) , first cut off 2 cylinder (one coil)  then bike run rough, if contininue driving pump cut fuel fuel supply(all in cdi brains)
as you parked bike abouth 5min reseve switch reset (cdi) and you can drive abouth 3-5 miles, then it will do it again IT was pain in ass to find
problem aboth 1000 dollars for pieces, hope no one dont have to fix 1dollar problem that way) now days dont use that switch bypassed by cdi and prefer gauge and tank .

yours SEPPO

[Mike Ramos]

Good morning fellas (notice I did not say Gentlemen; wanted to include everybody!).

Holy Toledo!

Noel, nice to see you so inclusive!  I think you covered almost everyone & some more than once!

Speaking only for myself, it is not the distance the fuel travels but the symptoms observed over several years, many a mile & repetitions.  That being said, I make NO definitive claim other than it is merely an OBSERVATION.

Mr. Cass – no apologies necessary as it is all in good fun – actually that word cannot be found on this Forum so let's "blame the useless search engine for not being any good"... in fact how can you be "short" with someone who is a Midget...?!

Uh oh...  Now I see Reply #26...   a possible refutation of the test which are (were?) irrefutable... Noel, you may not believe this coming from me but I hope you are not (once again) going away...

Oh my, never thought I would see the day where it may be better to discuss oil – would the gentleman from southern California like to begin...?!

Keep smiling!!!

And of course ride safe,

Midget

EDIT: Mr. T: just kidding

[racerrad8]

Once again this topic will just go away with no true, factual supported resolution; although it was again a nice debate. But there are questions that cannot and have not been answered.

I give up,   I concede and you guys can run with your synopsis.

I thought that was put to bed several years ago....the reserve switch re-activates the fuel pump...period.

I don't know why everyone's making such a meal of this, it's simple enough to check, and I just have.

My bike happens to only have a cupful of fuel in it and has been on reserve for a few days.
I just started it on the side stand, switched it back to main, waited for it to splutter, probed the live wire to the pump, nothing. While holding the test light on the terminal, switched to reserve, light immediately comes on, power restored to pump.

Repeat cycle 3 times, same results.

Noel

ETA: Looks like Noel just proved it's a FUEL-cut, not spark, for the pump-equipped models...

Someday someone, somewhere will actually have to apply a little more diagnosis and research and present the facts. But until then kindergarten diagnostics and personal interpretation/observations will have to suffice.

Man, I wish it was the weekend here, Friday has just begun.

I have a rally to work on, I'm out of this one for now...

Randy - RPM

[aviationfred]

I have a tank that is empty. I will pull the fuel sending unit out and investigate and see if I can get some definitive information this weekend.


Fred