Newby here. Does the fuel pump need to be continuously running? If not, how does the fuel get through the filter to the carbs?
In tank fuel pump...when should it be operating? Just at start-up or all the time?
- Thread starter TexasGJ
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Andrew Shadow
Site Supporter
Yes.
If the engine is running, so is the fuel pump.
If the engine is running, so is the fuel pump.
It will run when ignition switched on, for a short burst, then stops until engine fires up and causes vacuum to open fuel tap.
Not sure if it runs all the time if the vac switch has been bypassed, which is a mod carried out often when the vac tap plays up or fails/leaks.
Not sure if it runs all the time if the vac switch has been bypassed, which is a mod carried out often when the vac tap plays up or fails/leaks.
I think the way it works is it pumps continually. When the fuel bowl is full and the float shuts off the flow, the flow stops, but the pump continues to create a small amount of pressure in the fuel line. Then when the fuel is used and the float drops to allow more fuel in, the existing pressure in the lines flows fuel until the float once again shuts it off. The fuel pump relay energizes from pulses coming from the ignition module, so if its generating pulses the fuel pump is pumping.
Not 100% sure about this, so if I have it wrong hopefully someone with more knowledge of the system will chime in.
Not 100% sure about this, so if I have it wrong hopefully someone with more knowledge of the system will chime in.
Turn key on, fuel pump will run for a few seconds and shut off. Fuel pump relay get turned on again when it sees engine rpm. Runs until it's turned off by the ignition switch or the tip over sensor. Doesn't change with fuel bowls or Vacuum cut valve. But the cut valve can turn off fuel flow to carbs by blocking fuel flow thru the valve. It does not turn the pump off.
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I noted on the ST1300 the other day after repeatedly turning on and off the ignition - (to save the headlights flattening the battery while I was testing something) - that the fuel pump did not activate when I turned on the ignition. After I checked that the engine would start OK, I turned off the ignition and then turned it on again. The pumped whirred into life as normal.
I wondered if there is a device which recognises the amount of pressure, or a 'back EMF' circuit or a gray coded disc to detect whether or not the pump motor is turning at the speed consistent with the power that is being delivered to it.
I wondered if there is a device which recognises the amount of pressure, or a 'back EMF' circuit or a gray coded disc to detect whether or not the pump motor is turning at the speed consistent with the power that is being delivered to it.
Last edited:
wjbertrand
Ventura Highway
Not sure if the ST1100 has a crank position sensor, but I think so, certainly I know the ST1300 has one. Many cars and bikes are set up so that upon key-on, the pump runs momentarily to pressurize the system for EFI and to fill the float bowls in the case of carburetors. This may be a fixed timed run in the ECM the manufacturer has worked out so as to avoid the need for additional sensors. The fuel pump won't begin running continuously until the ECM starts receiving a signal from the CPS that the engine is rotating.
New electronic flasher relay arrived today and, whilst fitting it, I decided to check out the fuel pump operation as the feed pipe to the filter is easy to get to.
Sure enough AI st110 (No #5 above) is correct,
I was of the impression that the pump stopped due to back pressure in the fuel line from vac switch or floats in the carbs cutting off fuel flow.
I was wrong.
With the pipe from the tank disconnected the pump runs & shuts off when ignition switched on, then runs continuously when engine starts.
You learn something new everyday.
I also discovered when I went to pull the fuel pipe of the top of the tank, there was a small pin hole in the pipe which probably explains the cause of the occasional faint petrol smell I have been trying to find the cause of for some time.
So all in all I have not only learnt something new, but have saved my self a possible breakdown or a possible fire!
Thanks Guys!
Cheers....
Sure enough AI st110 (No #5 above) is correct,
I was of the impression that the pump stopped due to back pressure in the fuel line from vac switch or floats in the carbs cutting off fuel flow.
I was wrong.
With the pipe from the tank disconnected the pump runs & shuts off when ignition switched on, then runs continuously when engine starts.
You learn something new everyday.
I also discovered when I went to pull the fuel pipe of the top of the tank, there was a small pin hole in the pipe which probably explains the cause of the occasional faint petrol smell I have been trying to find the cause of for some time.
So all in all I have not only learnt something new, but have saved my self a possible breakdown or a possible fire!
Thanks Guys!
Cheers....
yep, that's consistent with these comments earlierSure enough AI st110 (No #5 above) is correct,
I was of the impression that the pump stopped due to back pressure in the fuel line from vac switch or floats in the carbs cutting off fuel flow.
I was wrong.
With the pipe from the tank disconnected the pump runs & shuts off when ignition switched on, then runs continuously when engine starts.
John OoSTerhuis
Life Is Good!
That would be highly unusual… a first in my 24+ years on the forums. Would love to see a picture of it. TIA
John
Sorry John, I think I didn't explain that quite right.
The pin hole was in the hose, not in the actual metal pipe.
Have cut the end off Pushed back on untill new hose arrives.
Do you have an 1100? The 1300 has FI.