Fuel Reserve

[great white]

What I enjoyed about the fuel pump FJ's is the long fuel hose running from the filter to the fuel pump.

When it was time to sync the carbs, I left the tank connected and simply rotated the tank 180 degrees and rested the tank on the subframe. This allowed plenty of room to the carbs.

Looking forward to your results .... Thank you in advance, for taking your time to do this.

Yessir, I rotated the tank once. Works, but I never became comfortable with it perched on the frame rails.

I'm usually a prime target for Murphy if I'm not watching for him, so I remove the tank and use my aux tank. I use one like this:



If it drops on the floor it doesn't spill, has a shut off valve on the bottom, holds plenty of fuel for extended running and I have a hook system that I hook on the bars or triples. A bungy holds it snug, just for insurance.

That Murphy, he's a b@st@rd.....

[racerrad8]

I believe Pat meant on the fuel pump bikes it is possible to spin the tank 180 and use the two rear mounting bolts to hold the tank in place. I believe I have seen my dad do this at a rally possibly. We also have an aux tank that is on a stand with fans and tools.

Robert - RPM

[great white]

I believe Pat meant on the fuel pump bikes it is possible to spin the tank 180 and use the two rear mounting bolts to hold the tank in place. I believe I have seen my dad do this at a rally possibly. We also have an aux tank that is on a stand with fans and tools.

Robert - RPM

Hmm, never thought of seeing if the bolts would work with the tank reversed. Would be a good work around on the side of the road or something.

I've thought of building a stand to hold my 4/5 gas and the rest of the stuff, but I just don't have the room for it.

An 83 Venture, an 83 Mustang, the FJ and all my tools don't make for a lot of space left over in a 1+ garage space.....

[Super]

Here is my experience with my 86.  No electric fuel pump on my model.  I wanted to satisfy my curiosity to see if/how the reserve switch worked.  I drove the bike until the red low fuel light illuminated solidly.  I had driven about 300k on the tank of fuel before the low light started to flicker, much was pretty "spirited" driving.  With the low light on solidly my gauge was two needle widths below "E", almost on the pin.  I drove it with the reserve switch off for approximately 60 kilometres, until running out of fuel.  Switching  to reserve didn't help, obviously the tank was bone dry.  I was carrying a 1l fuel bottle which eventually got the bike started.  It made no difference which position the reserve switch was in, the 1l continued to flow so I surmise my reserve valve solenoid has frozen in the reserve position as that small amount of fuel in the tank wouldn't normally be picked up in the "run" position.   I drove a short distance to a fuel station and added 21.5l of fuel.  The tank holds 22l so I know that it was fully drained when I ran out.

My points are:  the gauge works, the low light works, the reserve switch/fuel solenoid doesn't work and is stuck in the reserve position allowing the tank to be drained completely.  I see no point adding a manual type fuel valve, it would be pretty inaccessible under the tank.   Next time I have the tank off I may test the solenoid with 12 volts to see if it moves.  I can live with the gauge, light and odometer, but my bike is near mint and it would be nice to have it working as intended.

I'd like to know if 12v holds a properly functioning valve in the run or reserve position.  I'm assuming that the valve is normally in the reserve position with no power to it and when the bike is running and the reserve switch is not in the "on" position, the valve is receiving 12 volts to trigger the solenoid to take fuel from the taller of the two tank inlets.  Can anyone confirm?  I assume that when the bike begins to sputter, switching to reserve will remove the power from the solenoid and switch the valve to reserve.

Thanks,

Dave

[vegetta58]

I don't want to know how or why it works. I want to know in what position is the reserve disabled? RES or ON. I read through 10 pages and never saw a clear answer. Thanks and may this thread rest in peace.

[Pat Conlon]

On

[Super]

I would agree Pat, on my 86, depressing he rocker "up" to the "RES" position reveals a black sticker on the rocker "RES".  In the "down" position, the black "RES" sticker is hidden.
I'm good with all that, but as I found on my bike, the tank will drain to completely empty no matter what position the switch is in.  Bad switch, wiring or tank valve solenoid, all which I can check when I get the urge.

I'd hoped that someone can confirm without doubt how the system is supposed to work.  It would seem that the simple solution from Yamaha would be an electric solenoid fuel valve, similar in mechanical function to a manual reserve valve (with different length fuel pick-up tubes) controlled by the rocker switch.  No fuel pump disconnection, no coil interruption etc. 

Drive the bike with the switch down until the fuel level drops, at some point the fuel level will fall below the longer pickup tube and the bike will starve.  Flip the rocker and the solenoid will trigger fuel flow from the reserve tube.  Sometime during this process, the low fuel light will illuminate, hopefully just prior to requiring a switch to reserve. 

Lots of posts about this, but I've not found a definitive answer for the 86 model.

[racerrad8]

I can tell you this, there is not different draw tubes on the petcock. The petcock has a single inlet.

Unfortunately, in my opinion, there is not a "without doubt" conclusion oh how the reserve system works. As you have already read in the other posts, there is a lot of speculation and theory but no documented proof of the system functions

Randy - RPM

[Pat Conlon]

With Dave's experience on his '86, we can rule out ignition interrupt and a function of the reserve.

[Super]

I can tell you this, there is not different draw tubes on the petcock. The petcock has a single inlet.

From images of the part, I agree.  So my theory now is that something (gauge float lever or low fuel light) triggers the reserve valve to close.  Your engine starts to stumble, prompting you to move the rocker switch which either adds or removes 12v to the solenoid.  I'm betting that the solenoid is normally open, so somehow the low fuel/fuel gauge triggers something through the rocker switch to cause the fuel valve solenoid to change its state.

Hard to believe that 31 years later with all the knowledge here that it hasn't been discussed and confirmed.

I may get out the multimeter and check the wires to the rocker switch now that my tank is full and check it again when I drive it to empty.

Standby.

Dave

[Super]

And yes, my ignition was working fine when I ran out of fuel, from the time I noted the beginning of lack of fuel stumble to complete shutdown took me about a kilometer at 60kph.  Nothing shut down the ignition.

[Super]

I read a 2011 post on MCN from a guy with a similar problem that unfortunately has no solution.   The guy references a Haynes manual and a "fuel reserve control unit" located behind the rear master cylinder.  Anyone familiar with this module?  I don't have a Haynes manual.

[racerrad8]

With Dave's experience on his '86, we can rule out ignition interrupt and a function of the reserve.

Pat, are you sure Dave's bike is not stuck on reserve based on his new theory...?

Dave,

Based on this statement:

...Your engine starts to stumble, prompting you to move the rocker switch which either adds or removes 12v to the solenoid.

Dave

When you switched the reserve function, was the stumble gone instantaneously or did your bike stumble for several seconds while the gravity fuel flow refilled the carb bowls?

If the stumble was gone instantly, do you think the fuel can flow that quickly down into the carbs to refill them?

Also, do you think based on the wiring diagram provided earlier in the post, the switch might also have an effect on the CDI. (See reply #9) I know this is for a fuel pump version, but there is a total of six (6) input sources to the CDI and only three (3) outputs. On this diagram one of them controls the fuel pump, the other two outputs control the ignition coils.

Could the CDI alter the dwell/saturation time of the coils for diminished spark to cause the stumble?

By the way, I rode my wife's 86' bike this week and my experience is again; when the low fuel light comes on the bike begins to stumble, I rock the switch to "reserve" and the stumble goes away instantaneously...

So, unfortunately there is still doubt. Until I am to purchase a dyno and hook up an oscilloscope to see the secondary KV output of the coils I will continue to have my doubts of the experiences, theories and speculations on how the reserve system functions.

I have been told there is another forum member who has access to a different wiring diagram and also believes the CDI is part of the "reserve" function....more to come...someday.

I also have an experiment planned with Mike Ramos and the use of his auxiliary tank. When we get that sorted out in the next couple of months, the findings will be posted.

Until then, I will not continue to speculate on how the reserve system works, my post today was simple to advise there was no dual height draw tubes. My additional questions are based on your experiences and theory because Pat has clearly stated...

With Dave's experience on his '86, we can rule out ignition interrupt and a function of the reserve.

Randy - RPM

[Super]

I was driving very gently at 60 kph when it started to surge a bit.  This was after the low fuel light had been on for many kilometers.  I switched the rocker up to reserve but the bike ran out of gas about 900 meters down the road.  The tank was bone dry.  The 1 litre bottle of gas (took a lot of cranking to prime the carbs btw) carried me to the closest gas station where I pumped 21.5l into the 22l tank. 
Yes, I'd say the valve is stuck open.  I don't understand what triggers it to close, perhaps something that relates to this "fuel reserve control unit" referred to in another post?   

As I said, I drove over 30 miles with the reserve light on solidly before it began to stumble and ran out of gas.  There must be something that triggers the fuel valve to close when the low fuel light first illuminates.

Dave

[Super]

The bike will stumble and fart for some time when it runs out of gas, mine ran almost a kilometer before it died.  If I had an operating reserve and switched the reserve on at the first sign of stumbling, it would only take a matter of seconds for the float bowls to fill up and restore normal power, imo.  Randy, my low light flickers for a few miles prior to illuminating solidly.  Does your bike stumble when the light begins to flicker or does it start to starve only when the light is on solidly?