Flooded?

[yurinaut]

Bike: '88 K100RS

A while back I posted about a starting issue I thought was related to the battery and fouled plugs. I found out yesterday that although the battery needed to be replaced (it was) the starting issue was not spark plug related.

I stopped on the way home to pick up a few things from the grocery store. Was in there about 10 minutes after a half hour ride from work (leaving me about 1.5 miles from home). I loaded the groceries in the saddle bags and attempted to start the bike. It kicked over and tried to start then cut off. I felt a cold chill go up my spine...would it start or leave me stranded? The answer...stranded.

I hit the starter again and although the battery spun it nicely, no fire. I waited 5 minutes and tried again. Once again it tried to start and then more spinning with no fire. This is the pattern. Wait a few, try, it almost starts then, no joy. I didn't smell gas but I opened the throttle wide open and same, no joy again. I tried combinations of these techniques including trying to push start it down a hill and accomplished nothing more than making myself sweat profusely.

I got a ride from my wife to the parts store and got a new set of plugs in case they were fouled. Installed and had no change in the behavior whatsoever.

I had to get it towed 1.5 miles for $50 and 2 hours of annoying wasted time. I really want to keep it but I can't have a bike that will leave me stranded every third time I stop on the way home. Does anyone have experience with this type of behavior from K bikes and if so, is there a solution? I promise I'm not gassing the throttle when I try and restart a warmed up bike and the choke was completely off. Ideas oh' wise ones???

Thanks in advance and sorry this was so long,
Mike

 

[deilenberger]

OK - some terminology - the "choke" isn't - it's a fast idle device. BMW liked to think we're so dumb we wouldn't understand that and called it a choke. Using it when starting warm will have no effect except making it idle much faster when it does start.

When you say the starter spinned over - do you mean the engine was turning over, or you heard the starter spin up and no engine turn over? If so - search for "sprag clutch" and you'll find your answer.

If the plugs you removed were wet and the engine was turning over, then there was an ignition failure of some type. If the plugs were dry and the engine was turning over there was a fuel-injection failure of some type.

The 4 cylinder bikes do not normally flood (the 3 cylinder K75 is prone to this as the plugs get old.) On any K engine that has flooded - besides replacing the plugs, you should leave them out long enough (overnight usually..) for the cylinders to dry out a bit. Then on starting you should try starting with the throttle fully open (to allow more air in..) and once it sputters to a start, keep it at high RPM (2k or so) until it smooths out.

Question is - the condition of the plugs when you pulled them out. Something IS wrong since it apparently has done this before. Need more info to suggest further troubleshooting steps to determine what is wrong.

 

[yurinaut]

Thanks for the fast idle tip. I use that when it's cold and adjust it down to as low as possible once the bike is running just high enough to keep it from stalling.

By spinning I meant the engine was turning over. Doesn't appear to be a starter issue and the battery is new and was turning it over pretty rapidly.

When I pulled the plugs they were damp (it was dark) but not soaked by any means. It sure does wreak of an ignition issue. Unfortunately, I don't know where to start and when it runs, it runs beautifully. It's just strange that it does it sporadically if it isn't flooding.

Any tips on starting to diagnose a spark issue? Like I said, the plugs are new and the wires don't look very old at all. Plus, in the past (other vehicles) I've been able to detect when a plug wire was going south by the hesitations you get. Of course, these bikes could be different.

 

[deilenberger]

Any tips on starting to diagnose a spark issue? Like I said, the plugs are new and the wires don't look very old at all. Plus, in the past (other vehicles) I've been able to detect when a plug wire was going south by the hesitations you get. Of course, these bikes could be different.

The most common ignition failure on old K bikes is the Hall-Effect-Sensor (HES) that is used to trigger and time the sparks (and injection.) It lives under the T shaped cover on the front of the engine. What happens is it usually goes bad thermally - when it warms up it cuts out.

To test it - in the comfort of your garage..

Remove the T shaped cover. The HES is on the back of the round plate you'll see under it. No futher disassembly is required.

Steal your wifes hair-dryer. Put it on HOT - and with the engine idling - point it at the round plate. Heat the plate up until it's uncomfortable to touch. If the engine dies, while heating it up, chances are good the HES is going south.

To confirm this - cool the HES off by using the hair-dryer on air-only. If the bike now restarts, chances are excellent your HES is going kaput.

You can repeat the test as many times as you'd like.

Replacement of the HES is fairly simple - mark the position of the old one (the edge of the cutout on it is a good guide to use) - and install the new one in the same position. You may want to visit a dealer to get the timing checked after doing this. The connector for it is up on top of the engine - follow the wire.

If it's not the HES - then it will require some deeper troubleshooting...

 

[yurinaut]

Fantastic description of troubleshooting the HES. This would also explain why it doesn't cut off when riding the bike (the wind keeps it cooler) and then when stopped, the extra engine heat would cause it to fail. It also explains the secondary issue of flooding when the HES stops working.

I'll try that first and see if that works. Thanks again for taking the time to explain that to me!

-Mike