reserve switch

[Pat Conlon]

That would explain the reason for the wires on the 86/87 petcock.... (And thus the higher cost)

[NJona86FJ]

G'day
  Ok my fuel light is on the dash on the LH side between the speedo and tachometer,up high but below the neutral and turn signal. It gets brighter the less I have, and you can make it go out by stopping  hardish. I have ridden it too empty a few times without flipping the reserve switch. I honestly think it makes no difference on my bike. Know this for certain as I have a reserve switch no more. I am losing fuel though, not sure all this talk of fuel systems makes me think its time to have a bo peep in there maybe replace a few odd hoses. ( this will possibly be another thread)
  Just to throw a spanner in the works.
Cheers
Neil

[NJona86FJ]

  oh and just asking but if the ignition cut on 2cylinders would this not have potential to destroy engines? Hypothetically asking? The idea of draining the fuel bowls sound more inline with Japanese workings, the principle of " pay attention !!!  Remember motorcycle verrrrrrrry heaven!!!!"
Cheers
Neil

[Capn Ron]

oh and just asking but if the ignition cut on 2cylinders would this not have potential to destroy engines? Hypothetically asking? The idea of draining the fuel bowls sound more inline with Japanese workings, the principle of " pay attention !!!  Remember motorcycle verrrrrrrry heaven!!!!"
Cheers
Neil

It would certainly seem more logical...and beter for an engine to just cut the fuel when the bike is low on fuel...either by an old school dual-height petcock, an electric fuel pump cut-off or a petcock selonoid.  ...but then there's that pesky article early on in the FJ days that claims they *intentionally* misfire a couple of cylinders to get the job done.   

I'm inclined to put the late model FJ issue to rest tomorrow by throwing a multimeter on the fuel pump and simulating a fuel-low situatiuon.

Cap'n Ron. . .

[ribbert]

oh and just asking but if the ignition cut on 2cylinders would this not have potential to destroy engines?
Cheers
Neil

No

[racerrad8]

Cancelling cylinders by the cdi is much better than running the engine lean.

I can tell by the seat of my pants feel, the fact the engine will stumble on left corners and not on rights, it is spark and not fuel.

There is no way to cancel the pump, run the bowls dry and fill them up that fast.

I believe the "reserve" system has all to do with the cdi because Yamaha would not like to have to warranty a bunch of engines because they leaned they ran them out of fuel to "remind" the rider he is low in the tank.

Randy - RPM

[NJona86FJ]

  all good. The whole issue is interesting although mine doesn't do what's described I'd be interested to find out. Mine just stops when it's empty, yes your right randy it sucks runnin em dry.

[chocker]

Hi,
I have a 93 FJ and when the low fuel light comes the fuel pump does not switch off.

Mark

[movenon]

Cancelling cylinders by the cdi is much better than running the engine lean.

I can tell by the seat of my pants feel, the fact the engine will stumble on left corners and not on rights, it is spark and not fuel.

There is no way to cancel the pump, run the bowls dry and fill them up that fast.

I believe the "reserve" system has all to do with the cdi because Yamaha would not like to have to warranty a bunch of engines because they leaned they ran them out of fuel to "remind" the rider he is low in the tank.

Randy - RPM

Motorcycle manufactures have been cutting the fuel by various means for years. Most notably by the old dual-height petcock system with no lean burn conditions causing any problems that I am aware of ?   I rode them for many, many years... Even had an old 56 VW with a fuel lever to switch to reserve, gravity feed.

In the 88-93 bikes if you got a fuel cut out signal and made a left hand turn you would throw or cause the fuel level to lower on the right side which is where the sensor is located. Yes you will stumble first in a left hand turn. Sensor and fuel level is mounted on the front right side of the tank.

Still got my money on fuel not spark

George

[ribbert]

I can tell by the seat of my pants feel, the fact the engine will stumble on left corners and not on rights, it is spark and not fuel.

Randy - RPM

I can't see how that would indicate one or the other.
Wouldn't that just be the sender unit bottoming out as the bike leans left and activating the reserve function?

Yamaha would not like to have to warranty a bunch of engines because they leaned they ran them out of fuel to "remind" the rider he is low in the tank.

Randy - RPM

I don't believe a 4 stroke briefly running lean under those circumstances would be an issue. It's only running lean for as long as their is sufficient fuel and spark to ignite it, which isn't very long.
If you lean out a motor with an EGT gauge, the temp rises immediately but it takes longer for that soak into the engine.

I'll still go with MY "seat of my pants" feel.

Noel

[Pat Conlon]

.....Still got my money on fuel not spark

Yep, me too  again, what do the wires to the 86/87 petcock do...??

Good discussion....all good points, I will learn something here....

[movenon]

.....Still got my money on fuel not spark

Yep, me too  again, what do the wires to the 86/87 petcock do...??

Good discussion....all good points, I will learn something here....

I would start a "Poll" but I am afraid it would start another thread.   
George

[racerrad8]

I can't see how that would indicate one or the other.
Wouldn't that just be the sender unit bottoming out as the bike leans left and activating the reserve function?

Yes, so the sender is sending the signal and cutting the ignition not draining fuel fuel bowls and refilling them every 100 yards while I ride in the twisties. There is not enough time to drain the carbs and refill them in that time span.

I don't believe a 4 stroke briefly running lean under those circumstances would be an issue. It's only running lean for as long as their is sufficient fuel and spark to ignite it, which isn't very long.
If you lean out a motor with an EGT gauge, the temp rises immediately but it takes longer for that soak into the engine.

I'll still go with MY "seat of my pants" feel.

Noel

Well, mine will run on the reserve function for almost 30 miles...that is a long time to be "lean" and will damage the engine. So the EGT (exhaust gas temps) rise immediately...hmmmm, I wonder if the piston also sees a immediate increase in temps...?

...But wait, the piston is aluminum and expands at twice the rate of the steel sleeve. Also, the piston is what is exposed to the leaner hotter, hotter mixture. Since the piston is the source of air movement by its up & down pumping movement, I bet it gets really hot, really fast too, maybe even faster than the exhaust. So, I think the most important part of making the engine run, gets hot pretty quick and has the opportunity to seize in the bore due to the expansion rates. I will be showing Pat his seized sleeve when he picks up his bike.

I tell you what, here is practical application test everyone can do.

   I want everyone to disconnect their fuel pump. Start their bike and see just how long it takes to deplete the fuel in the carb bowls with the engine running. Then hook up the fuel pump and see how long it takes to refill them.

You will then be able to tell how much time it takes to do that with the "low reserve" function while you are riding. And if that was the case, you still have to activate the switch and you still have the required time to fill the carbs before the bike fills the carbs and rides away. But, in fact, when you activate the switch the bike instantly runs better. Maybe there is "turbo fill" to fill the carbs faster when the switch is activated, maybe the pump pressure jumps up and the pump volume increases. Oh, but wait there is still the small fuel supply hoses and needle seat orifices, maybe those expand upon the additional pressure & volume.

Think about it, do you think Yamaha made the early non fuel pump bikes cut the ignition and then change the CDI system to then cut out the fuel pump on the later models, which would require an extended amount of time to cycle the fuel bowl fuel level?

Yamaha is just like every other manufacture, keep using it as it is already developed and paid for...

If, you think that, show me the wiring schematics and a volt meter inline with your fuel pump showing the "reserve" function working and the fuel pump with no voltage.

All you have to do is bring the tech and prove it to me otherwise.

Randy - RPM

[Pat Conlon]

Remember, you don't need to run the bowls dry, when the bike is running on the needles the fuel level needs to drop just to a point below the mains before studdering begins.

Why don't you just disconnect the fuel line and run it into a bucket, and energize the wires going to the petcock and see what it does to the flow of fuel?

[weymouth399]

Mine works on both my 86 and 89, and yes I was very glad to find out they did work, as was my wife.

Bob W