For the last 2 years, I have a funny problem with the 1985 RT-sidecarL.

The bike is running well and suddenly, it starts to run on 2 cylinders. On idle it's running almost perfectly but if I open the throttle it sputters.
If I stop the bike and restart the engine, same problem. If I stop the engine for at least 2 minutes, it will run perfectly again for sometimes up to 2,000kms.

What could be the problem? Not the Hall sensors, because they don't have time to cool down within 2 minutes.
Ignition or FI....
Anybody experienced the same problem?

CF

If you let it cool down to cold and then restart the bike. Feel which exhausts are cold. Each coil runs two cylinders 1/4 and 2/3. Sounds very possible its a coil issue. Once you find which two are cutting out you can swap the coils. If the non running cylinders change then a new coils likely. If it stays same check the electrical connections into the coil and also the plug leads. If you have a spare bike or a friendly K owner you could swap them.

I can't say that I have had similar problems but as soon as I read the post I thought fuel and a partial blockage.
Reason is that many years ago my father and I and a friend of dads used to go fishing in a boat that the friend had built himself. For ages the engine would just splutter and then come good or occasionally stop. Dad got him to pull the top off the carby and sure enough no fuel but as soon as he tried to start it ,it would pump fuel up and away we'd go.
It ended up after months of frustration to be a large Gum nut (seed nut from a eucalyptus tree) rolling around in a flat bottom tank and every so often would get sucked over the inlet tube and stop the fuel but  of course when the engine stopped so did the suction and the nut would drop off the tube and the pump would fill the carby and away we'd go, sometimes for the rest of the weekend and sometimes for only 10 minutes.
I have heard of a flap of rubber from the inside of a fuel line doing similar things but at a far more regular rate.
Idling OK means to me that a very small quantity of fuel is always getting through and that stopping the engine removes the blockage until the right set of circumstances arise and it happens again like maybe when there is a high demand on fuel.
I think you have a second tank in the sidecar do you draw fuel directly from that or pump up to the regular tank and always use fuel from there. Just looking at places a problem could be as you have more than usual.

92KK K100LT 193214 wrote:If you let it cool down to cold and then restart the bike. Feel which exhausts are cold. Each coil runs two cylinders 1/4 and 2/3. Sounds very possible its a coil issue. Once you find which two are cutting out you can swap the coils. If the non running cylinders change then a new coils likely. If it stays same check the electrical connections into the coil and also the plug leads. If you have a spare bike or a friendly K owner you could swap them.

The bike restarts perfectly within 2 to 5 minutes. It's almost impossible to check anything as without moving the bike or turning the handle bar it starts to work again. The time lapse between the failure and the bike running is so short that you don't have any time to do any testing.
Within 2 minutes, the exhaust don't cool down and this is why I don't know where to start.
If it was a bad connection, it wouldn't fix itself.

If you could swap one coil with another one and see does the problem show itself again.you can try one coil and then another. It sounds like a coil problem.

RicK G wrote:I have heard of a flap of rubber from the inside of a fuel line doing similar things but at a far more regular rate.
Idling OK means to me that a very small quantity of fuel is always getting through and that stopping the engine removes the blockage until the right set of circumstances arise and it happens again like maybe when there is a high demand on fuel.
I think you have a second tank in the sidecar do you draw fuel directly from that or pump up to the regular tank and always use fuel from there. Just looking at places a problem could be as you have more than usual.

Thanks Rick.

Today, the first thing that I did was to open the tank's gas cap to be sure that the tank was not in depression or sucking mode (This can happen when the air vent is plugged).
I am now thinking that the Pressure Relieve Valve may have a problem. With the sidecar attached to the right of the bike, this is a big job to access it.
The auxiliary tank on the sidecar is just to refill the bike's tank.

92KK K100LT 193214 wrote:If you could swap one coil with another one and see does the problem show itself again.you can try one coil and then another. It sounds like a coil problem.

This is easy as I have spare coils   . This is not a bad idea as I have to start troubleshooting somewhere.

Check the HT leads, they go when cold, not when hot if faulty

could be leads ....was my first thought ....with the added load of acceleration - revs ...snuffing out the spark ?
I had a similar experience a while ago ....bike felt off tune or at times would load back to 2 cylinders ... till I bumped one of the high tension leads back into the tower on a ride with twb out to drake for lunch (to meet rick ) ....was a while ago now ...I guess the really bumpy roads out there just wiggled the lead out a bit more so it became a more permanently noticeable fault .

All good tips. I don't hink it'll be the FPR, as that would affect all units equally.

With a lead problem I wouldn't expect two units to fail, but what do I know :-)

I would try to identify which cylinders fail (water spray on exhaust or even better a laser thermometer?? but meantime have a good look at the wiring/connectors under the coils (the 'input' side of them) It might be that one is wonkey and therefore not always have that coil working correctly, which would affect two units at the same time.

Hi, I think that the most probable culprit would be a coil, go for the swap.
Best regards
JAP

If the coil, HT lead swap don't give succes......it could be a idea to check the
hall sensor connector under the tank, the rubber cap that should protect it is
usually rotted away after just a few years.

charlie99 wrote:... till I bumped one of the high tension leads back into the tower on a ride ....was a while ago now ...I guess the really bumpy roads out there just wiggled the lead out a bit more so it became a more permanently noticeable fault .

I had this too, one of the leads just "fell" out, bike began running on 3 , thought it had thrown a plug, limped to the nearest cycle shop, replaced the plugs, no, change . checked where they plug in to the coil and there it was, just hanging there. Another time I replaced the leads due to intermittent misfiring on 2 of the four cylinders. Basic trouble shoot says fuel, plugs, leads, then off in to deeper territory

Bert,
A quick way to check if the pump is supplying pressure to the fuel rail is to squeeze the fuel line at the input of the fuel rail while pressing the starter button. You can feel the pressure build up in the line.
Just a thought.
Paul.

sidecar paul wrote:Bert,
A quick way to check if the pump is supplying pressure to the fuel rail is to squeeze the fuel line at the input of the fuel rail while pressing the starter button. You can feel the pressure build up in the line.
Just a thought.
Paul.

Thanks Paul, that's a good tip. I was also checking if the fuel was returning to the tank to be sure that the pump was working.

I've just had another idea, could the problem be caused by cavitation at the fuel pump?

Later pumps had an 'anti-cavitation' vent tube fitted to the pump filter, so that implies that earlier pumps could be affected. I suppose that after a couple of minutes standing, the air bubble would disperse and things would revert to normal running.

Paul.