The Khan - a fools attempt at a K100 build

[Laitch]

Cut down mudguard implies shit hitting the fan!

  :clap:  It's a certainty and might even lubricate it!

[rbm]

I don't think that's the correct board.  There's to few components and connections on it; there should be a couple of adjustment pots, a couple of BD240 transistors, a couple of BD877 Darlington drivers and I don't see them.  Did you trace the circuitry from the external connector to that card to verify that it is the correct board?

[DJC]

Here we go.

[rbm]

Yes, that's it!! The schematic for this card is attached to this post.

[DJC]

So, T1 and T2 look to be the thermistors.
The four pins at the base are Gnd, +,  T1, T2. Diagram suggests that those two T1/T2 pins are the thermistor inputs. Top right two pins are the +12V for each corresponding thermistor.

[rbm]

None of the components on the card are thermistors.  The thermistors are on the inside of the fuel sensor in the tank.  Here is a cross-sectional photo showing the insides of one.



Check the schematic I posted against the board and carefully trace out the circuitry to make sure you have the correct connections.  My guess would be that the four connections at the bottom of your photo are the thermistor inputs from the sensor and the power connections.  The two connections at the top of your photo are the 4L and 7L outputs given their proximity to the two power transistors ... but that's a guess.

[DJC]

Yes, apologies. That's what I meant.
The T1/T2 pins in the four block are the thermistor inputs from the tank.

[revisitedmotorcycleco]

So what happened w the M-unit & that install?
Can you post a few pics & a write-up?

[DJC]

M-Unit is in and sorted.
The wiring at the moment works. Its not pretty and has all the redundant old wiring harness still.
Next project is is clean the wiring up, use nice plugs etc.

At the moment it's all in the original relay box under the seat.
I need to get/make a wiring diagram of what is needed from the EFI unit / temp and all that. Then strip all the old wiring out.

If you want an easy installation, 100% go the BEP from Maru Labs.
I only went the M-Unit because I wanted new hand switch controls to clean the handle bars up and I'm a bit of a twit.

[DJC]

None of the components on the card are thermistors.  The thermistors are on the inside of the fuel sensor in the tank.  Here is a cross-sectional photo showing the insides of one.



Check the schematic I posted against the board and carefully trace out the circuitry to make sure you have the correct connections.  My guess would be that the four connections at the bottom of your photo are the thermistor inputs from the sensor and the power connections.  The two connections at the top of your photo are the 4L and 7L outputs given their proximity to the two power transistors ... but that's a guess.

Hey RBM,

Whats stopping me just plugging one of 600Ohm thermistors onto the speedos input itself?
Granted i'd only have two states - full and empty, but it will only be 1 less stage of "full-ness" than with the board/relay/resistor setup we talked about.

Or will the tank thermistors just not function at all if they don't get the correct voltage fed from the board..?

[rbm]

Your latter statement is the most correct one... "will the tank thermistors just not function at all if they don't get the correct voltage fed from the board..?"

Both thermistors are supplied a 95mA current by the circuit to heat them up.  They sense the presence of fuel because the thermal mass of the liquid cools the heated thermistor and the thermistor assumes a given resistance.  When the fuel depletes and the thermistor gets exposed to the air , the resistance changes and that shift in value registers in the circuit.  You need that special circuit board to sense the change and switch on the indicator light (or in your case, switch on the relay).

Hooking up the raw thermistor to the fuel gauge will not work at all, period.

[DJC]

Right. I thought that might be the case.
Give a couple of weeks and I'll test the rig and report back.

As always. You're the best RBM.