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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: NMPete on February 17, 2026, 11:28:55 AM
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Hi - I am close to getting my K75 project finished and ran into a problem I can't solve:
When I start it and it idles, the starter and fan keep running! I've searched the Forum, but can't find a similar issue.
I have tried switching relays, no help
Good almost new battery full charge
With fuel pump disconnected, hit the start button and engine cranks then stops with button release
All dash lights etc working with ignition on
Clutch handle wired open
Any suggestions?
Why is fan running?
Many thanks for any ideas
Pete
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Here's one possible, simple, explanation, the starter relay might be in the stuck closed position, the temperature relay might also be in the stuck closed position.
Some workshop manuals have the relays incorrectly labelled, verify them against the wiring colours in the wiring diagrams.
To simplify the way forward, you could deal with the starter relay problem first, then look at the fan problem.
Removing the temperature relay will probably prevent the fan from working (this would also indicate that the fan problem is with the relay or upstream of it) Now check the starter relay, you should not have continuity between pins 30 and 87, if you do, that's a problem. A start attempt with a sad battery often results in a stuck relay. If you put a new battery in, it could still be stuck. If it has continuity, hold it two feet above a concrete slab, let it go, pick it up, it might now be fixed.
With the temperature sensing relay, you should not have continuity between pins 15 and A2, if you do, that's a problem.
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If the wire from the temp sensor to the temp relay has its insulation worn and is grounding then that will keep the fan running. Check resistance from ground to terminal E of temp relay socket. If that is less than 200 ohms then the fan will run.
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Hi Folks - Thanks for the helpful tips!
Here is the good and the bad:
- The wierd rattling noise on first start-up: I was afraid it was dangerous, so quickly turned it off. Checked things over and decided to try again and and this time the rattle was a little less, so let it warm up and reved it a little and after a while the noise went away. Great! Never did figure that one out.
- The fan issue: Checked the wire from the temp relay (E) and finally found the connector hidden under the tank and cleaned all - no short. So checked the temp sensor per the "Troubleshooting Guide" and it has a resistance similar to the guide chart.
- Started it again and no fan running but temp light is on in the dash. Took it for a first ride around the block (Slow to return to idle) and it ran good. What a smooth bike! I think I will like it a lot if I can sort out the little things.
- Got back, let it idle a while to get hot and fan did not come on; finally boiled over.
Guess I will drain and test the thermostat, however the fan should have come on?
Comments?
Thanks
Pete
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You've done a bit of tinkering which seems to have helped, so keep going with that.
Sometimes a lot of problems disappear after just a service. The cooling system also wants a good looking over by the sounds of it.