K100RT Heat Problems

[Oz Dave]

Whenever my 1985 K100RT gets hot (in town or highway after about 40 mins) the engine starts to intermittently cut out. It gets worse and worse until you have to stop and let it cool down for 15 mins. I need to solve this as my commute is 55 mins, so the last 10 mins either way i look like a complete twit as my bike lurches along the road, with some maniac with throttle control problem riding.

My two guess's are fuel starvation due to a build up in heat, which i believe was a problem on these earlier bikes, or the halls sensor playing up as it gets hot. As much as this feels every bit like fuel starvation, i have to ask myself the question that surely that would have been fixed by a previous owner considering it has done more than 150k miles (it a bike that has done a lot of k's). They would have never been able to put up with that sort of behavior and do all those miles if it was an original design problem such as not enough airflow.

Any other areas i should check. Your advice is greatly appreciated.

[Bruce C]

It sounds like your problem is vapor lock related.

Most of the old K-bikes already have the heat-fix kit in them. That included insulation on the underside of the tank and rubber & tin wind deflectors bolted on the inside of fairing and the engine.

I would first change the fuel filter in the tank(real easy on an old "K".

Bruce C

[Oz Dave]

Thanks Bruce,

I have already changed the fuel filter as that was my first thought. Any idea were i might get one of these heat kits? Cheers!

[Bruce C]

Dave

I have NO idea if those kits are still available. Maybe you can lift up the tail of the tank and see if there is any aluminum backed insulation glued to the tank.

How about pulling the lower fairings off to see if that helps.

Real easy to do. Take off the fairing storage compartments, then the fairing knee pads, and finally remove 3 screws holding the upper fairing to the lower fairing inside the fairing compartment holes, 2 screws at the radiator shell to lower fairing and a couple of brackets holding the fairings to the motor.

[Oz Dave]

I'll do that. I've had the whole fairing of a while ago so i know it doesnt take long. i'll ride like this for a commute or two and see if it stops the problem. Thanks.

[bmwmick]

I'll do that. I've had the whole fairing of a while ago so i know it doesnt take long. i'll ride like this for a commute or two and see if it stops the problem. Thanks.

 

Dave,

To localize the problem, remove the T-Cover over the Hall Effect Sensor Plate and carry some Quick-Freeze ( http://www.miller-stephenson.com/aero_002.htm ) or something similar. When it fails, spray the area and see if it starts running good immediately. If so, you've found the culprit.

You could also try cracking the fuel cap open when it acts up. Maybe the tank isn't venting properly? That problem is pretty rare on a fuel injected bike though.

You may also be able to look down in the tank when this occurs and see if the fuel is boiling. If the fuel boils, the intake port of the fuel pump CAN be sucking vapor. This is NOT vapor lock but it acts similar.

 

HTH,

 

Mick

[Oz Dave]

Mick,

Thanks Mate! I have already cleaned out the fuel vents and have been riding with the fuel cap slightly ajar even though i now know this is not a problem with vacuum build up in the tank. That, fuses for the fuel pump and the fuel filter were my first thoughts when this fist happened a while ago.

I should explain that this is my spare/second bike, which i bought a couple of months ago (on the cheap). I have been mainly wrenching it with very little riding as i have had up until just recently a 1150RT which was may main ride. I thought that i would have cleared up the problem with all the servicing and cleaning out of things but I see that isn’t the case.

I have just check the bike for insulation (its in the city and I’m in the country so I had to wait a couple of day to get hold of it) and it is as I remembered when I took the tank off. There is insulation under the tank and a think insulator pipe running down the outside of the main fuel line. I new no-one could put up with this sort of behavior from a bike as soon as it got above 20 degrees C/ 68 degrees F when it is 20 years old.

I guess my main question now is whether the halls effect sensor is likely to cause these sort symptoms (read, like some one else is rolling the throttle on and off by remote control just to make you look like an idiot in traffic) and is there anything else such as leaks or the main computer that could cause this when the bike warms up.

I will definitely try your check on the halls sensor with the freeze spray (if I can get some).

If this is the halls sensor (which I’m beginning to think it must be) can I fit a new one here in the city and then ride 45mile home and then do the timing on the engine. Or will this greatly affect the engine and I should I do it straight away? I have some experience with car engines and as long as the timing is not wildly out it isn’t a problem. The replacement sensor is likely to be second hand as its way cheaper and also the guy will give me another if its no good in the first little while. Thanks for your help.

 

BTW, there nothing wrong with the throttle control or the linkages to the top of the engine. They are all fine.

[Alien_Hitchhiker]

Dave, just how hot is your bike getting? Is this at least partly an overheating problem?

 

1) Does the fan come on as the bike gets hot?

2) How's the coolant level?

3) Does coolant flow through the radiator when the engine is hot (thermostat and/or water pump)?

 

The K engines, being water cooled, normally operate in a fairly narrow temperature range. The engine should not be running hot.

 

Steve