'86 blown fuse = fuel starvation

[Old Rider]

Yesterday i was trying to find out what makes a knocking sond going over bumps on my 86 1200 (I have recent replaced the headbearings and also re tightened them) .while doing that i sat on the bike
wich stod on centerstand.i grabbed innside the rubberboot at the headlight and pulled it up and down while doing that i could feel
the bulblight spring coming lose i then repositioned the spring.The knocing sound did come from my headlight the reflector innside is knocking aginst the housing. Then i fired the bike and heading for home then after riding mayby 3kilometers i suddely lost much power and engine making noises similar to when you run out of fuel i also discovered that i had no blinkers and the free gear light didnt work also the horn was dead.i almost made it home with engine running on 1 or 2 cylinders but then it was completely dead.
This sonds similar to your experience when you bike stopped.I then pulled of the seat and it was the 15ampere fuse blown (instrument).
I replaced the fuse and bike started again after the carburettors filled up again and i rode home.Today i took a look at the headlight
bulb connector and it was very badly melted with much of the metal connectors visble i replaced it with a ceramic connector.
So here is what i think has happened: the spring on the bulbfastener did chortcut the connector when i was pulling on the mounting even if the ignition was off.
this also explain why the engine stopped after a while of fuel starvation.Because the fuelsender unit also shut down because of the blown fuse.Dont know if this helps you and im sure you have checed the fuses .

[Pat Conlon]

....this also explain why the engine stopped after a while of fuel starvation. Because the fuelsender unit also shut down because of the blown fuse.

I would like to learn more about this "fuel sender unit" that's powered by the headlight circuit on your '86. Please enlighten me.

Thanks  Pat

[Old Rider]

Well i dont know why the fuel sensor/sender unit did shut down but it sure did because i ran out of fuel.When replaced the fuse the signal lights worked again and also the instrumental light the green free gear light.Then when restarted the bike i took some time before it fired becaus the carburettors neded to fill up again. the stange thing was that my headlight still worked when the fuse had blown.The fuse i replaced was marked as signals i the fuse box lid.Mayby the sender unit cuts out the petcock for safety reasons when that fue is blown.And hey im just trying to help so i dont need bullshit

[FJ_Hooligan]

Could the petcock solenoid have been on the circuit with the blown fuse?

Without power, the solenoid would stop fuel flow?

[Old Rider]

i took a quick look at the circuit diagram now and it seems that even if i shorted the wired in the headlight connecor it could blow the fuse for the signals nr33 15Amp  and not the headlight fuse nr 39 in diagram. the fuel sender nr14 fuelmeter nr13 fuel indicator nr15 and horn nr17 horn switch nr18 relay unit nr20flasher unit nr21 and all turn/signal lights and more goes on that fuse because its connected with the circuit going for headlight  and dimmerswitch nr40 and more..

[Pat Conlon]

...And hey im just trying to help so i dont need bullshit

Sorry, I came across that way, it was unintentional. I was curious, trying to understand what you posted.

[Old Rider]

Nothing to be sorry about its me who misunderstand and i was a little grumpy
well anyway today i was out riding and the same happened again after mayby one hour of riding my 15A signal fuse blows again and engine stopped of fuel starvation .It happened twice so it was not the headligtconnector who had chorted.
So i just hawe to lay down flat I was lucky and did find the reason it was the rear brake light connectors one of them was out of socket and schorted against the metal on the top of the adjust mecanism for the shock when i pressed the brake.It was hanging loose so it only touched the metal in some angle .I had yesterday
changed wheelbearings on rearwheel and bleed rear brake and when fiddling with the brakereservoar the wire for rear brake had come out of the socket and shorted.

[Pat Conlon]

Ok, so it sounds like blowing that 15a signal fuse is shutting off the fuel tank petcock, thus the engine starvation.
Sound about right?

The opening/closing of the petcock occurs with engine vacuum (we know that) but when you lose power in the signal circuit (blown fuse) this loss of power closes the petcock. I did not know this could happen.

Question: How much gas did you have in the tank? Where you by chance on reserve when this happened?
I'm thinking that if you were on reserve, (switch in reserve position) the petcock needs 12v power to stay open. When this power stops, the petcock returns to the normal run position, starving the engine.

If you were not on reserve, then the petcock needs 12v power to stay in the normal run position. In this case if the power is interrupted, the petcock should move to the reserve position and you shouldn't starve for gas.


Of course all this would occur on the '86-87 FJ's which have the switch reserve feature.

The '84/85's have a straight vacuum petcock with no reserve function.

[Old Rider]

Ok, so it sounds like blowing that 15a signal fuse is shutting off the fuel tank petcock, thus the engine starvation.
Sound about right?

The opening/closing of the petcock occurs with engine vacuum (we know that) but when you lose power in the signal circuit (blown fuse) this loss of power closes the petcock. I did not know this could happen.

Question: How much gas did you have in the tank? Where you by chance on reserve when this happened?
I'm thinking that if you were on reserve, (switch in reserve position) the petcock needs 12v power to stay open. When this power stops, the petcock returns to the normal run position, starving the engine.

If you were not on reserve, then the petcock needs 12v power to stay in the normal run position. In this case if the power is interrupted, the petcock should move to the reserve position and you shouldn't starve for gas.


Of course all this would occur on the '86-87 FJ's which have the switch reserve feature.

The '84/85's have a straight vacuum petcock with no reserve function.

The tank was over half full and the switch is in the reserve position pressed down at front end.I always have the switch in that position.

[Pat Conlon]

That's interesting. The petcock was energized in the reserve mode, yet when the power was interrupted the petcock closed?
I thought it should have reverted back to the normal 'run' function. You had plenty of fuel. I don't know how that could starve the engine.

[Bezmozek]

Similar thing happened to me on my FJ600, but the reason was poor charge from generator as connection was melted.
Is there possibility, that if you have short circuit, there is not enough power for spark/fuel pump?

[Pat Conlon]

No fuel pump on the '86.....Gravity flow.