fuel gauge flashing and odd readings

can anyone help and tell me whats going on?
we were away last weekend, covering some 2000kms with no problems, apart from in the mornings when the bike was started the whole fuel gauge would flash with no readouts and after a period of time (various) it would go back to normal readouts, I have now noticed that even with a tank filled to the brim one moment it reads full then it will drop 2 bars or more then read full again after a while. any thoughts? the bike is running fine, average fuel consumption 43 to the gallon (us) I thought it might be a fuel pump/pressure problem but this does not seem to be the case.

Chris-the-sweep

Possibly a sender/float problem?

I'm going to guess it is the thermo resistor, or whatever it is called on the fuel pump assembly. Mine went out (under warranty), took the mechanic forever to find out the problem before replacing the pump unit. It is possible to replace that resistor (might be able to find info about it in the forum by seaching for it. Good luck!

Don't know what the readout does with a full tank and the thermistor in the lower tank acting up?
The bars dancing around sounds like maybe the upper fuel sender. A float hooked to a pot (variable resistor) After you burn say a quarter tank does the read out settle down? You can pull that and check it with a multimeter.

The thermistor in the lower tank just knows if it's in gas or in air.
Check this thread for a replacement option.
https://www.st-owners.com/forums/showthread.php?111929-Why-not-sell-the-fuel-pump-assembly

Fuel pressure shouldn't have anything to do with the readout.

I still have a very full tank, maybe one bar should be gone, so far its told me I have everything from a full tank to a third of a tank it varies each time i start the bike and when riding (this makes me believe its is the sender unit sticking) but as to why the whole display would just show bars for the consumption and the whole display flash with no readout for fuel level or consumption even when riding?

Check page 22-17 in your service manual.
All bars blinking including the lower --.- digits.
- open or short in fuel level sensor or wiring
- faulty fuel level sensor full should be 1-6ohms empty should be 213-219 ohms.
- short in the fuel reserve thermistor or wiring
- faulty thermistor
- faulty combination meter.

Since you also get a goofy reading a few bars too low and then back to actual level without flashing it sounds like the upper sensor or wiring.
Could be a dirty connection, chafed wire etc. or a dirty pot dropping out in its range of travel in the upper sender float assembly.

many thanks, thats just the information i need, I dont have a service manual for the bike yet, but as my riding season is just about done up here in the great white north I will check everything out when i store the bike at the end of the month, i have a feeling it will be easy to find, as my wife said she could smell burning plastic at one point on our trip last weekend!!! so a short in the wiring now makes perfect sense, will keep you posted as to what I find.

When my thermo resistor decided to quit working, my fuel gauge also quit working, along with the mile per gal readout. (Actually, it didn't just quit, it would work, then not work and then work and not work, until finally, it wouldn't work at all.

They (the Honda shop I took it to) wound up replacing the entire pump assembly to fix it. But first they tried replacing the upper sending unit, that didn't work, then they tried replacing the speedometer assembly, that didn't work, so by that time, there weren't too many other things to replace, so they tried the pump assembly...that fixed the problem.