Author Topic: Ignition / Spark issue while bike is hot and at high RPM  (Read 3728 times)

Offline Mike Flores

  • ^ Motobrick Curious
  • Posts: 75
Ignition / Spark issue while bike is hot and at high RPM
« on: May 19, 2018, 04:35:19 PM »
Hello everyone,


A couple months back, I was riding back home from a taco shop here in LA (it was a warm day and the bike was warmed up) and when I hit the throttle the engine bogged down above 5-6k RPMs. I pulled over, and shut the bike down. I initially suspected a vacuum leak at the throttle bodies or crankcase breather hose, but ruled that out (Also, all of my vacuum lines, hoses, and even the rubber intake manifolds are new on my bike). This process probably took me about 3-5 minutes. The bike fired right back up, and I started riding again. After a couple blocks the same problem happened. I shut it down again for a few minutes and contemplated what it could be. I fired it up again, and rode home without any problem.


I thought maybe it was an electronic fluke - I have been having intermittent issues with my speed sensor in my bike, and thought maybe I was having electronic issues in general. The shutting down and restarting seemed to cure the issue, and I went about life. I haven't been riding my K100 much, and instead I've been daily riding my Multistrada just because it's a bit more practical for everyday commuting.

Fast forward a couple months, and I take my K100 out for a ride on Angeles Crest Highway with a couple friends. After riding 20-30 miles, stopping for gas, giving the bike plenty of time to get up to temperature the same problem pops up. Only happens when I'm on the throttle, and while the bike is hot. At this point I realize that it's probably a bad coil or bad coils - because it idles fine, starts fine, and the issue only presents itself at higher RPM. I figure the bike (and coils) are hot, and unable to produce spark. So I let the bike cool down for a while, and ride back home. I make it home without further incident (again, a 20 mile or so ride at freeway speeds).


When I get home, I fire up the laptop and start searching and reading motobrick for other people with similar issues. Lots of good info. I learn all about the problematic HES sensor, how to diagnose it, how to fix it, where to get cheap sensors online and make the budget repair... all of that. I haven't tested anything yet because I haven't had the time to work on the bike because of my work schedule lately. That being said, I'm 95% convinced it's the HES, and 5% leaning towards bad coil(s) or plug wires.


My question is this - what is the best possible replacement for the HES?


I've read elsewhere that the real culprit is insufficient wiring insulation between the sensors and the harness plug. I'd like to fix this issue in the most bulletproof way possible. That likely means not going with an OEM HES assembly, since the insulation is likely to fail again in the future at some point - right?


I've found this, and it seems like it might be the best option - as well as being significantly less expensive than the OEM HES assembly. What are the collective thoughts on this unit?


http://www.euromotoelectrics.com/product-p/boignsen-k033edl.htm


Any advice would be appreciated. Also, most of the threads dealing with this issue and the replacement individual sensors are several years old at this point, so it might be appropriate to have a more current thread dealing with this.
  • Los Angeles, CA
  • 1987 K100

Offline Martin

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  • Posts: 4437
Re: Ignition / Spark issue while bike is hot and at high RPM
« Reply #1 on: May 19, 2018, 05:14:20 PM »
I had problems with my 75 cutting out and failing to rev up when I hit the throttle. It occurred on really hot days mainly in traffic. It was due to a couple of things, the underside of my tank was never fitted with insulation and the hoses to my FPR were never insulated. Rectifying this partially cured the problem.

The other thing that was happening was that when the bike got hot, the non OEM fuel return line was collapsing where it went into the tank. Fitting a Unicoil over the hose where it enters the tank has cured that problem. Due to the fact that we are now in autumn and the days are cooler I won't know whether the problem is fully cured.

 I did also fit a home made fuel cooler which worked fine at cooling the fuel substantially at highway speeds, but didn't do a lot in traffic where it was needed most. I also found that the problem could be alleviated more by running with a full tank in traffic.
Regards Martin.
  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Offline E30_Crazy

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  • Posts: 105
Re: Ignition / Spark issue while bike is hot and at high RPM
« Reply #2 on: May 19, 2018, 06:21:14 PM »
Sounds a lot like how my current issues started, and am still fighting. I hope yours is a simple fix. I have 3 pages on here testing parts, wires, etc...


As an FYI, I got the cheaper hall sensor just the other day, and it didn't quite fit under the "T" cover. The screws that hold the metal clips that hold the wire harness are a bit too tall and wide. Had to grind down some of the material on the backside of the T cover
  • Newport News, Virginia
  • '85 K100, '93 K1100RS
God created Crew Chiefs so Fighter Pilots could have heroes, too.

Offline Mike Flores

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  • Posts: 75
Re: Ignition / Spark issue while bike is hot and at high RPM
« Reply #3 on: May 19, 2018, 06:48:44 PM »
I had problems with my 75 cutting out and failing to rev up when I hit the throttle. It occurred on really hot days mainly in traffic. It was due to a couple of things, the underside of my tank was never fitted with insulation and the hoses to my FPR were never insulated. Rectifying this partially cured the problem.

The other thing that was happening was that when the bike got hot, the non OEM fuel return line was collapsing where it went into the tank. Fitting a Unicoil over the hose where it enters the tank has cured that problem. Due to the fact that we are now in autumn and the days are cooler I won't know whether the problem is fully cured.

 I did also fit a home made fuel cooler which worked fine at cooling the fuel substantially at highway speeds, but didn't do a lot in traffic where it was needed most. I also found that the problem could be alleviated more by running with a full tank in traffic.
Regards Martin.


Martin, thank you for this thoughtful reply and insight. I don't think this is my issue though;


a) I have the OEM insulation fitted to the underside of the tank.
b) I have OEM fuel lines all around, and I know there are no kinks.
c) I've already gone through an entire Los Angeles summer with my bike, in temperatures exceeding 105F (above 40C) with no such problems.
d) Along with all the rubber hoses, vacuum nipples, etc. I also replaced the fuel pump and fuel filter with OEM units, and my injectors are new 'upgraded' 4 hole units.


I don't think it's a fueling issue.
[size=78%] [/size]

E30_Crazy, I'll look into your thread.

  • Los Angeles, CA
  • 1987 K100

Offline Scott_

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  • Posts: 2190
Re: Ignition / Spark issue while bike is hot and at high RPM
« Reply #4 on: May 19, 2018, 08:08:59 PM »
It's possible the electronic ignition control module could be on it's way out. Age and heat could be causing it to begin to fail.
Electric contact cleaner couldn't hurt the connector, worth a try.
  • My Garage
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Offline caveman

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  • Posts: 196
Re: Ignition / Spark issue while bike is hot and at high RPM
« Reply #5 on: May 20, 2018, 08:20:05 AM »
Could be the air flow valve/door binding up and not opening or not sending proper signal to the ECU. I would think a failing HES would kill engine when hot.
  • Kennerdell, PA.
  • 87 K100RT, 88 K100LT

Offline Mike Flores

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  • Posts: 75
Re: Ignition / Spark issue while bike is hot and at high RPM
« Reply #6 on: July 18, 2018, 12:50:45 AM »
I just wanted to update this thread, it ended up being the HES. I've had no issues since replacing it.
  • Los Angeles, CA
  • 1987 K100

Offline Laitch

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Re: Ignition / Spark issue while bike is hot and at high RPM
« Reply #7 on: July 18, 2018, 07:31:01 AM »
Thanks for the update. Did you use the Euro Motoelectrics product?
  • Along the Ridley in Vermont.
  • 1995 K75 89,000 miles
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Offline Mike Flores

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  • Posts: 75
Re: Ignition / Spark issue while bike is hot and at high RPM
« Reply #8 on: July 18, 2018, 09:26:45 PM »
Thanks for the update. Did you use the Euro Motoelectrics product?

Yes, I did use the Euro Motoelectrics HES.
  • Los Angeles, CA
  • 1987 K100

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