throttle mystery

[kaput]

Greetings:

Recently I bought an 85 K100RS of indeterminate mileage :dunno2:

It was too cheap to pass up so I though I would simply re-sell. I used to think my K bikes were boring but that was probably because at the time there were also Airheads, Ducatis and Guzzis in my garage.

Older and wiser, I now consider my KRS to be magical, especially when it comes to seating position, comfort, build quality, overall balance, fairing performance, and engine braking. After 80mph the bike is even, ahemm.... exciting! 

I had recently experienced a hunting idle, so this morning I replaced the crank vent hose. The hose was clearly bad so hoping for joy I took the K for a ride.

The bike ran great for about 5 miles until suddenly the engine raced toward the redline independent of the twist grip. :eek:

Thankfully there was not a lot of traffic. I killed the engine, pulled over, and checked the throttle and cable. Everything looked normal, no sticking cable, and the twist grip and throttle closed normally. I restarted the engine with throttle fully closed and the injection system again immediately gave full throttle.

The only thought I have so far concerns the idle switch, which is in close proximity to where I was twisting my screwdriver working on the crank hose.

The nice troubleshooting guide by Bertrand Vogel suggests: "A bad switch may send a wrong signal to the EFI computer. When this switch is disconnected, the EFI thinks you are twisting the throttle."

Is my understanding of this correct? Would a bad idle/throttle switch possibly cause this to happen? Am I on the right track here or :hehehe

Any diagnostic help would be greatly appreciated because this bike will never see the dealer.

Help me get riding. :riding:

[johnny]

is your choke on...

j o

[kaput]

Thanks for responding. Choke was off.

[Scott_]

because this bike will never see the dealer.

That's probably a good thing as the bike is most likely older than the staff in the shop....... :hehehe

Clean and check the connections at the tps switch and the multipin plug at the jetronic computer. They can do funky s__t when dirty.

[Grim]

For it to rev means the engine has to be pulling the air through the AFM. The AFM control the fuel. Knowing this you can stop looking for a air leak between the AFM and head.

It sounds like the throttle is not closing. It's possible that the throttle cable has frayed and not allowing the throttle to fully close. I'd start by disconnecting the throttle and choke cable from the throttles and see if it will idle normally.
If not I'd pull the air box and look and see if the throttle blades are sticking.

I use to have a toyota supra that had a very similar fuel injection (the injection is built under license from Bosch). I had the rubber elbow that connected the intake to the AFM it was in bad shape and when I re installed it a piece on the under side actually broke off and got stuck on the throttle blades days later and kept the throttle from fully closing. Not saying that's what happened but when you replaced that crank case breather hose was it crumbling? 

[komandoalicante]

on one occasion I was passing the same and that the throttle cable was bent and took shape and from time to time stopped in that position well check the cable sheath...

[kaput]

I had the rubber elbow that connected the intake to the AFM it was in bad shape and when I re installed it a piece on the under side actually broke off and got stuck on the throttle blades days later and kept the throttle from fully closing. Not saying that's what happened but when you replaced that crank case breather hose was it crumbling?

Grim: I could see how this could happen but the vent hose was still in one piece. Good idea about disconnecting the throttle. Will try that when I have time this weekend. Thanks.

Scott: Thanks. The connection to the tps switch and the multipin plug look OK.

Komandoalicante: Thanks for the input. Throttle cable looks to be in good order.


 :dunno2: :dunno2:


Any other ideas please let me know.

Still not clear on one thing: Can a bad tps switch cause the engine to rev independently of the throttle? 

[Inge K.]

Still not clear on one thing: Can a bad tps switch cause the engine to rev independently of the throttle?

No, the TPS only senses two positions.....fully closed throttle, cuts the fuel if above 2000 rpm
and fully open throttle, fuel enrichment.

But a misadjusted TPS can prevent the throttle from from closing completely.

[kaput]

Thank you Inge.

[johnny]

if my throttle was sticking open i would be looking for some nice sweepers...

j o

[mystic red]

if my throttle was sticking open i would be looking for some nice sweepers...

j o

That;s some funny shit right there... :clap:

[komandoalicante]

Still not clear on one thing: Can a bad tps switch cause the engine to rev independently of the throttle?

No, the TPS only senses two positions.....fully closed throttle, cuts the fuel if above 2000 rpm
and fully open throttle, fuel enrichment.

But a misadjusted TPS can prevent the throttle from from closing completely.

There are several problems that can occur with the Accelerator.

That the chain fist is not well oiled.

The output of the cuff (below the brake fluid reservoir 8 V) this deteriorated.

The cable tensioner is not in condition, there are two models to one that is protected output by a rubber fist or half of the cable under the tank.

Or ramp butterflies this spoiled.

Release the cable and test each separately.

[kaput]

Riding again. :riding:

Had to send back though my mail order degree in advanced brick fuelinjectionology.

It ended up being a piece of broken fairing rubber cleverly disguised as part of the throttle stop.

Sometimes you feel like an idiot. :yes

Thanks for all the help and info.

[kaput]

if my throttle was sticking open i would be looking for some nice sweepers...

j o

Nah. Not if you live in curve less South Florida.