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1Back to top Go down   1990 K75S no start Empty 1990 K75S no start Mon Aug 13, 2018 9:31 pm

Jim H

Jim H
New member
New member
The bike had sit for 5 years and I decided to start riding again (long story).  It was working when I put it away.  I decided to change out the tank guts with ethanol resistant parts.  That all when fine.  Now it won't start.  Symptoms include flooded wet with gas plugs on cranking.  It might fire and run on one, then two then all cylinders but won't idle  Then after it warms above 2k rpm it will run on choke and then finally idle.  It will restart immediately but won't after sitting for 30 minutes.

Have done a lot of testing.  Fuel pump and regulator working and putting out ~37 psi during cranking.  It has spark on all three plugs and plugs have been replaced.  The injectors can be heard clicking away with a stethoscope and their resistance in 16 ohm each. I built a lamp system and hooked each injector lead up to it.  All flash when cranking.      The air flow meter (AFM) checks out per Bert Vogels tome on the subject.

The coolant temperature sensor is reading 8300 ohms at the computer connector (pin 10-13)and the online number says it is supposed to be ~2500 ohms at RT.  

I removed the connector from the from the coolant T sensor today and measured the sensor resistance there at 4100 ohms.  No corrosion, clean. When connect it the reading at the computer is 8300 ohms.  There seems to be something wrong there. What else does the coolant sensor connect to? How do we get the resistance at the computer back to 2500 ohms? One diagram I looked at showed it didn't connect to anything.  Another showed it connected to the temperature switching unit. The diagram shows the sensor body is grounded the the pipe to which it connects  I haven't checked that yet.

Finally would such high sensor reading at the computer allow for the flooding problem discussed?

Any help would be appreciated.



2Back to top Go down   1990 K75S no start Empty Flooding? Mon Aug 13, 2018 10:27 pm


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Sounds like you did your home work and checked all the right things. If all the connections look good I would suggest you pull the fuel rail with injectors and see if they are leaking when pressured up.


3Back to top Go down   1990 K75S no start Empty Re: 1990 K75S no start Tue Aug 14, 2018 5:19 am

92KK 84WW Olaf

Life time member
Life time member
If the coolant sensor is giving one reading 4100b and the reading at the computer is 8300 check the connections too. Those pins can need cleaning to get the electrical connections correct.

Doing the injectors is easy enough but when you are doing it have new seals to hand plus a few spares, clean out the area well before you remove the injectors. The rail comes off as a unit with the injectors on it but you have to disconnect the fuel lines. If those are original they will be cracking so replace them. There are two on the injector rail but you have three fuel lines and you should replace all three. Make them slightly longer than original too so you can move the tank around for servicing without disconnecting it.

If the computer thinks the engine is cold due to faulty temp sensor it will over fuel.

But it will also over fuel if there is a damaged vacuum line to the fuel pressure regulator [FPR], rear of the throttle bodies is the vacuum line and if a hole in that you will overfuel by 60-70%. The vacuum is also affected if the little caps are faulty and again you will over fuel. Finally the FPR itself can also go faulty with overfuelling the result.

Leaky injectors will normally show up as wet plugs if you check them before starting the bike.

Its unlikely enough for all injectors to go faulty at the one time.

If your injectors have the cover that goes over them be careful, despite its location its not petrol resistant and petrol will eat it double quick.

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