1985 K100 Comprehesively Screwed

[Motorhobo]

Weird. Tonight, I hit the button, and it idled smoothly for over ten seconds, then it started struggling, slowing down.

 I may drain the tank just to see if that does anything.

That really sounds to me like an ignition problem rather than an anything else problem to me. I've had it so many times over 18 years and three K75s...just again last week. Ran on all three cylinders for 1 mile, then on two for no apparent reason. Pulled the plugs, cleaned them off gently with solvent and a wire brush, let them dry, sprayed contact cleaner on the connection ends in the OEM wires and on the plugs, reinstalled, contact cleaner on the 4 pin under the tank and on the ECU contacts under the seat, has been fine since then and will hopefully be fine until the new wires and plugs I ordered get here.

Total time expenditure, about 15 minutes.

[k]

That really sounds to me like an ignition problem rather than an anything else problem to me. I've had it so many times over 18 years and three K75s...just again last week. Ran on all three cylinders for 1 mile, then on two for no apparent reason. Pulled the plugs, cleaned them off gently with solvent and a wire brush, let them dry, sprayed contact cleaner on the connection ends in the OEM wires and on the plugs, reinstalled, contact cleaner on the 4 pin under the tank and on the ECU contacts under the seat, has been fine since then and will hopefully be fine until the new wires and plugs I ordered get here.

Total time expenditure, about 15 minutes.

Mechanic said the coolant sensor is reading cold, despite being changed three times in 200 miles. The inaccurate reading is said to cause the fuel/air mixture to be way off, causing running problems. I may investigate the wiring to and from the coolant sensor.

[Laitch]

Mechanic said the coolant sensor is reading cold, despite being changed three times in 200 miles. I may investigate the wiring to and from the coolant sensor.

This information should been posted at the early stages of the thread. I'd ask your mechanic what "reading cold" means and how that was determined.

If the sensor is sensing that the coolant is cold when the engine is cold, the engine should start and run for more than ten seconds but the engine will run poorly if the sensor doesn't sense that the engine is warming up. If the sensor is sensing that the coolant is warm when the engine is cold, the engine will have trouble starting. If it can be started using the throttle and kept running long enough, it's likely to settle down and run ok if all other systems are correctly adjusted—until the engine is shut down and cools again.

If you have purchased three defective coolant temperature sensors in a row, there might be some bad juju involved. The coolant temperature sensor in your moto's engine can be tested in position or removed for the boiling water test. Ask your mechanic how it was tested.

Did you drain the fuel tank and inspect the interior?

All this is going to take up time. Are you certain you wouldn't rather be riding off on the Harley to some exotic locale instead?  :idea2:

[k]

This information should been posted at the early stages of the thread. I'd ask your mechanic what "reading cold" means and how that was determined.

If the sensor is sensing that the coolant is cold when the engine is cold, the engine should start and run for more than ten seconds but the engine will run poorly if the sensor doesn't sense that the engine is warming up. If the sensor is sensing that the coolant is warm when the engine is cold, the engine will have trouble starting. If it can be started using the throttle and kept running long enough, it's likely to settle down and run ok if all other systems are correctly adjusted—until the engine is shut down and cools again.

If you have purchased three defective coolant temperature sensors in a row, there might be some bad juju involved. The coolant temperature sensor in your moto's engine can be tested in position or removed for the boiling water test. Ask your mechanic how it was tested.

Did you drain the fuel tank and inspect the interior?

All this is going to take up time. Are you certain you wouldn't rather be riding off on the Harley to some exotic locale instead?  :idea2:

Fuel tank is pristine. I cleaned it when I replaced the fuel pump and filter, last year. It remains to be determined whether the gas in it might be bad, but the interior looks clean and shiny.

It is mathematically impossible to buy three faulty sensors in succession. I will accept as a given that the sensor is fine.

"the engine will run poorly if the sensor doesn't sense that the engine is warming up." This is a hypothesis worth exploring.

Thanks for the suggestions on the bike. As for the personal content, any reason you're busting my balls?

[mw074]

 "It is mathematically impossible to buy three faulty sensors in succession. I will accept as a given that the sensor is fine."



 New doesn't mean good.

[Laitch]

Thanks for the suggestions on the bike. As for the personal content, any reason you're busting my balls?

I was simply suggesting the return to a pathway of happiness already mentioned by you in Reply #13. If that idea is causing groin pain, that's beyond my control.

[k]

I was simply suggesting the return to a pathway of happiness already mentioned by you in Reply #13. If that idea is causing groin pain, that's beyond my control.

I only provided personal details in #13 because you prodded me into such revelations.

All I'm trying to do is fix this bike.

[Laitch]

10-4

[Motorhobo]

Thanks for the suggestions on the bike. As for the personal content, any reason you're busting my balls?

Laitch is one of the more knowledgeable people on this forum. Having said that, and no disrespect intended, he's also -- shall we say -- somewhat persnickety about new poster's manner of expression and his own manner can be -- shall we say -- somewhat off-putting. A good rule of thumb might be to take the useful information in that particular context and ignore the rest.

[Motorhobo]

Mechanic said the coolant sensor is reading cold, despite being changed three times in 200 miles. The inaccurate reading is said to cause the fuel/air mixture to be way off, causing running problems. I may investigate the wiring to and from the coolant sensor.

While I respect your mechanic's credentials, swapping out any part three times because of 'bad readings' might indicate that this person is dependent on measured values taken from some documentation that might or might not be correct. If I were in your shoes, I'd be trying to wean myself of dependence on this particular mechanic. Your profile doesn't say where you are. If you add that information and ask for some recommendations via PM you might get a reference to someone locally who's specializes in K-bikes or is willing to give you a hand in tracking down this gnarly gremlin.

[k]

While I respect your mechanic's credentials, swapping out any part three times because of 'bad readings' might indicate that this person is dependent on measured values taken from some documentation that might or might not be correct. If I were in your shoes, I'd be trying to wean myself of dependence on this particular mechanic. Your profile doesn't say where you are. If you add that information and ask for some recommendations via PM you might get a reference to someone locally who's specializes in K-bikes or is willing to give you a hand in tracking down this gnarly gremlin.

I don't want to name any names, but this mechanic is famous around these BMW parts.

That said, a lot of BMW mechanics are stronger on Rs than Ks.

I tend to agree with your view of the mechanic and the rigidity of analysis.

[k]

Your profile doesn't say where you are. If you add that information and ask for some recommendations via PM you might get a reference to someone locally who's specializes in K-bikes or is willing to give you a hand in tracking down this gnarly gremlin.

I'm in the Midwest. I'd really appreciate a directory of K mechanics.

[Motorhobo]

Sorry, I'm nowhere near that or I'd help.

Have you cleaned the ignition switch?  The reason I say that is that I recently had a similar issue that was resolved by (veeery carefully) taking apart the ignition switch and cleaning it up, see the link "No Start ~ Slow Start ~ Whackness" here:

http://www.motobrick.com/index.php/topic,11033.0.html

I didn't want to believe that it was the switch since it manifested in inconsistent ignition, but I finally bit the bullet, took out the switch and cleaned it to the tune of a couple hours. Lo and behold -- it was the culprit.

Your bike is over 30 years old, and if that switch has never been cleaned, it needs it. Be VERY careful! Do NOT try to clean it in situ! Disconnect it and take it to the bench. There is a tiny ball bearing that servers as the detent. Lose it and weep. There is is a white plastic bucket that will crack if you pry it too hard, then you'll be looking for a new switch. Take pictures of every step in the disassembly. If you do that, it will only take 45 minutes. Good luck.

[rbm]

I find it very hard to believe that your coolant sensor has failed three times in 200 miles.  That part can last the life of the bike.  I published an Excel sheet listing measured resistances against sensor temperatures, which produces a typical NTC temperature curve.

If I were you , I would validate the mechanic's work by checking the condition of one of the failed sensors, if you still have it in your procession.   Measure the resistance of the sensor between one of the spade connectors and the body of the sensor while immersed in a pot of water, the temperature of which you gradually raise by heating it over a stove. Be careful -- Don't measure the resistance between the two spade connectors.  BTW, Are you sure your mechanic was aware of this procedure and followed it?  It's quite easy to get wrong, which would lead to a failed diagnosis. an artificially high resistance would make the sensor appear "cold".

[Laitch]

Measure the resistance of the sensor between one of the spade connectors and the body of the sensor while immersed in a pot of water . . .

Just to forestall unintended consequences, I'll add that it is the sensor you immerse in water, not yourself.