Reserve switch. What does it actually do?

[wakdady]

I did a search and read that it was a simulated electronic reserve. but what the hell does that actually mean?
further search mentioned something about the petcock doing something as well.

i was low on fuel the other day and flipped the switch not knowing if it really did anything. when i was cleaning out my tank i also noted that there is nothing electronic about my petcock. just a simple "on" "off" valve for when you remove fuel lines.

so if the petcock doesnt do anything. What's going on in there?

[tqmx1]

On the fuel pump bikes it shuts off the pump so you have to go to reserve to start the pump again. Sounds screwy but that's YAMAHA for you.

[WS]

The fuel sending unit gives a signal to the black box which turns off one ignition coil. The bike starts running on two cylinders and it feels like you are running out of gas. By switching to reserve you turn on the coil again.

[wakdady]

At what point does that occur? Right when the light turns on? Or after its been on for a little?
Thanks for the proper info btw!

[WS]

It happens after the light turns on. You still can go for a while with the low fuel light.

[Pat Conlon]

At what point does that occur?

.....the point when your bike starts running on 2 cylinders COULD BE exactly when you don't want this to happen... Like when you're passing a string of RV's on a uphill grade with opposing traffic coming at you....Yea, that is exciting.

With a working fuel gauge, low level light and a trip odometer, do you really need a reserve switch?

[chapindad]

Thanks for asking the question.  I have be trying to figure it out myself and kept forgetting to ask myself.

[Travis398]

What year FJ are we talking about?  They're not all the same you know.

[tqmx1]

Let me change my statement. The 89/90 cut fuel pump power the 91 and up just might shut down a coil.

[weymouth399]

I'm glad my 86s works. The light comes on just as I need to turn reserve on. So far so good 5000mi later and it still works, tried it the other day.
If it's there, it will be hooked up. It might save me a dumb shit of the day award, I get enough of them lately thank you.

Bob W

[LA Mike]

Let me change my statement. The 89/90 cut fuel pump power the 91 and up just might shut down a coil.

I have also wondered how this switch works, I know some have posted they have disabled this function. I have a '89 so what needs to be done to the switch/bike to disable it?  I normally just watch my miles to know when I'm low on fuel.

[RichBaker]

The fuel sending unit gives a signal to the black box which turns off one ignition coil. The bike starts running on two cylinders and it feels like you are running out of gas. By switching to reserve you turn on the coil again.

This is INCORRECT.... on all years FJ(except 84 & 85), the fuel flow is shut off, 86/7 use a solenoid at the petcock, 88-on shut off the pump.....

[Kopfjaeger]

At what point does that occur?

.....the point when your bike starts running on 2 cylinders COULD BE exactly when you don't want this to happen... Like when you're passing a string of RV's on a uphill grade with opposing traffic coming at you....Yea, that is exciting.

With a working fuel gauge, low level light and a trip odometer, do you really need a reserve switch?

cool.... im guessing i found my flaw.... chuckles... my light comes on but its only when it irratates me that i hit my res switch.... havnt had it drop out or cut out on me..... only once when it was dead empty and within the last 10 meters ( 30 odd feet in old speak  ) of the servo. agree with ya pat... watch the little numbers go round and know the mileage/kilometerage is always good.... also as my fuel needle has popped itself all the way round to the other side of "E" and i couldnt be bothered fixing it for the gazillionth time..... so im just a numbers guesser now..... interesting read this to know what happens i actually thought it just switched off the pump and turned it to gravity/ vacuum feed

[Harvy]

The fuel sending unit gives a signal to the black box which turns off one ignition coil. The bike starts running on two cylinders and it feels like you are running out of gas. By switching to reserve you turn on the coil again.

This is INCORRECT.... on all years FJ(except 84 & 85), the fuel flow is shut off, 86/7 use a solenoid at the petcock, 88-on shut off the pump.....

Agreed!


Harvy

[Harvy]

also as my fuel needle has popped itself all the way round to the other side of "E" and i couldnt be bothered fixing it for the gazillionth time.....

Neil, I have a fuel gauge here if you want it........its still on the right side of the stop....... removed it when I installed the Acewell dash.

Harvy