Fuel reserve systems?

[Timbo-1]

Hi guys, been doing some maintaince on my 1WK 87 the last couple of days and after removing the tank to gain access etc thought I would flush the tank and clean pet cock etc. While I had the pet cock apart cureousety got the better of me to how the reserve system operates. Seems when the fuel becomes low enough, the sensor in the tank sends a signal to the fuel light and to the solenoid in the pet cock. The solenoid effectively bypasses the vacuum to the main valve so it doesn't work and remains closed, permitting no fuel to flow, am I correct??
The solenoid signal, (ie voltage), is eliminated or cut by the reserve fuel switch, basically returning the pet cock to normal. I have found the reserve switch confusing in the past to which position is on or off, push forward for reserve....
Then I found this on the web, have read of the last part in the electrical system section about fuel reserve...

http://motorbike-search-engine.co.uk/classic_bikes/yamaha-fj1200.php

Does anyone know what years/models have this function?
Food for thought,
Cheers Timbo.

[Bones]

Hey Timbo, grab a beer or three and have a read through this.


http://www.fjowners.com/index.php?topic=9996.msg95770#msg95770

[Timbo-1]

Hey Timbo, grab a beer or three and have a read through this.


http://www.fjowners.com/index.php?topic=9996.msg95770#msg95770

Opps....   Thanks Bones...

[Earl Svorks]

  It's been ages since I logged in but today I'm home from work with some free time. Either way,,I followed the link that Bones put up and after digesting this I'm in agreement with Noel. My '90
works as he describes. IMHO,,, why would the reserve switch need "instructions" to be any different  from what is seen on any conventional gas tap?  ON or RES. Most folks seem to know what to do with that.
It's good that there's no PRI position on the FJ rocker switch! Can you imagine?

[flips]

Hi Guys.

I read the thread with interest also.
With out making any comment on the later models,  when my 86 runs low on fuel the engine stumbles like its losing spark
and instantly returns to normal when the reserve is turned on, which seems to confirm what Randy has experienced.

Cheers,

Jeff P

[Pat Conlon]

Then, what do the wires going to the petcock do?

I noticed at the race track, bikes with quick shifters have a popping sound as they up shift at WFO.
Sounds like little backfires, which actually is accurate. The quick shifters use ignition interrupt. The popping sounds comes from the accumulated unburned air/fuel which is then is ignighted when the spark returns.

So, I was thinking, if the FJ's use ignition interrupt as the fuel reserve, wouldn't the same popping symptom be present as the spark returns when you flip the switch to reserve?

We know that the fuel pump FJ's ('89-93) use a fuel pump interrupt, not a spark interrupt. There's no doubt.

I suspect the '86/87 FJ's use an electric valve on the petcock to do the same thing.
It's just a suspicion on my part because I do not own a '86/87 or I would know for sure.

[FJmonkey]

The '86/'87 has a small solenoid powered by the wires going to the petcock. Having taken my old petcock completely apart and finding the solenoid, I am very sure the reserve system on the '86/'87 stops fuel flow and not spark. If I get bored I may dig around in my old parts to see if I can take a photo of it. 

[FeralRdr]

The '86/'87 has a small solenoid powered by the wires going to the petcock. Having taken my old petcock completely apart and finding the solenoid, I am very sure the reserve system on the '86/'87 stops fuel flow and not spark. If I get bored I may dig around in my old parts to see if I can take a photo of it. 

Bingo! 

I also took my old petcock apart to see how the mechanism worked.  However, I already new that it worked on a solenoid mechanism as the '86/'87 FJ1200 "Supplemental " GYSM, provides troubleshooting steps for the "Fuel Reserve" Mechanism.  As I recall, they said to disconnect the petcock's electrical connector from the main wiring harness, and then 'jumper' the connector to the battery.  You should hear the solenoid "Clicking" (if it is working correctly), when you complete the circuit.

[racerrad8]

...when my 86 runs low on fuel the engine stumbles like its losing spark and instantly returns to normal when the reserve is turned on, which seems to confirm what Randy has experienced.

Jeff P

Then the link provided by Timbo says this:
Electrical system

The FJ1200 features a standard 12 volt electrical system. The alternator and starter motor are mounted behind the cylinders. Yamaha's self cancelling indicator unit is used and a variable resistance gauging system is used to monitor engine oil contents with associated warning lights. A large fuel gauge is provided as is a low level warning light. Nippondenso Transistor Controlled Ignition (TCI) is used in conjunction with two coils. The FJ1200 fuel reserve system is unusual in that when the fuel level reaches approximately 5 litres remaining ignition is cut to two cylinders giving the impression that the vehicle is running out of fuel, a reserve switch mounted in the fairing restores the cut cylinders allowing the rider to continue normally.

Those are key statements above.

I made a video of Pat's engine with carbs that were full running until out of fuel and the engine stumbles. I set up a fuel pump to see how long it would take to get fuel back to the carbs to get it running  smoothly after it "ran out of gas". This simulates the petcock solenoid shutting off the fuel at the petcock as some believe occurs.

The video shows the engine hits its first stumble at 1:42/3 and then really falls on its face at 1:44 and it takes until 1:47 to come back to full song. That means at the minimum there is a 2-3 second delay before the engine starts running smoothly again, with a fuel pump no less.

I can only imagine the recovery of a gravity feed bike would be longer than that.

That is anything but instant recovery after switching the reserve switch like Jeff states above.

As I stated prior, there are two (2) fuel system inputs to the ignition system

Here is the ignition circuit with inputs & outputs.

There are two input circuits to the CDI regarding the fuel level and reserve systems and only one output to the fuel pump.

"I" - Fuel censor input circuit
"J" - Reserve switch input circuit
"H" - Digital ignitor unit
"P" - Fuel pump driver circuit

Like I said the last time around this system, I do not fully understand how it works and do not have the skill & ability or time to figure it out. I just have the GYSM above along with my personal experiences available to base my findings and I believe the ignition circuit is interrupted.

I would hate to be riding my bike in the twisties and have it stumble for a significant amount of time to recover...seems like a crash waiting to happen. Where a slight change to the coil saturation causes a stumble, the rider flips the switch and he has it back under full power instantly, not 2-3 seconds why the fuel pump recovers the fuel level in the carbs.

That is my take on all of this.

Randy - RPM

[Burns]

coming back home from my Yellowstone jaunt we were running 90 plus for a goodly stretch. nary a glitch. As I pulled into a rest stop the motor stumbled once and died. I coasted to a stop. The bike would not restart.

Of course the fuel gauge was well past "E" and had been there quite a while. There were exactly 200 miles on the tripmeter. Like I said we'd been running pretty fast since the last top-up.

From this experience I'd guess the reserve solenoid acts like a traditional petcock, i.e. the "main" part of tank draws from an intake that is higher than does the "reserve" part of the tank.

I'll check that by looking at the intake side of a petcock, or a picture of one. Some day.

[Pat Conlon]

Negative Burns. There is no high or low fuel level intake points on your petcock. There is no solenoid on your petcock. (like the gravity flow '86/87's)

The reserve system on your '89 either works via the fuel pump interrupt or by ignition interrupt, thus the debate.

[CutterBill]

The reserve system on your '89 either works via the fuel pump interrupt or by ignition interrupt, thus the debate.

Simple test... hot wire the pump, then ride the bike until the Low Fuel light comes on.  If the engine keeps running, it's a fuel pump interrupt.  If the engine stumbles, it's an ignition interrupt.
Bill

[movenon]

coming back home from my Yellowstone jaunt we were running 90 plus for a goodly stretch. nary a glitch. As I pulled into a rest stop the motor stumbled once and died. I coasted to a stop. The bike would not restart.

Of course the fuel gauge was well past "E" and had been there quite a while. There were exactly 200 miles on the tripmeter. Like I said we'd been running pretty fast since the last top-up.

From this experience I'd guess the reserve solenoid acts like a traditional petcock, i.e. the "main" part of tank draws from an intake that is higher than does the "reserve" part of the tank.

I'll check that by looking at the intake side of a petcock, or a picture of one. Some day.

There is a sensor in the tank that starts the events happening. The Petcock is just a small wire screen with no high and low intake.
Here is the float system showing the sensor. 1990 Fj


Here is the petcock

George

[Burns]

The reserve system on your '89 either works via the fuel pump interrupt or by ignition interrupt, thus the debate.



thanks for the info Pat.  It does not make sense to me that yamaha would turn off the ignition to two jugs and let the gas flow to those carbs. Surely both the gas and the sparks are stopped.  Does the fuel pump have any sort of provision for such a cut-off?

[Pat Conlon]

The fuel pump is controlled thru your ignition box.

We know there is a safety circuit that shuts off the power to the fuel pump after 3-5 seconds if the engine is stopped.
After servicing your carbs and you reinstall them with the fuel bowls empty, when you turn your key on, notice that the fuel pump runs for only a couple of seconds then shuts off? You have to turn the key off, then on, a couple of times for the pump to fill the bowls.....that's the safety circuit.

Could the reserve system be both, fuel and spark?  That seems redundant to me, but stranger things have happened.