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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: RobP on March 26, 2015, 09:44:23 PM

Title: Troubleshooting my barn find
Post by: RobP on March 26, 2015, 09:44:23 PM

Bike:  1985 K100RS, 48k miles

Disclaimer:  I am fairly mechanically-inclined, but I have never owned or worked on a K bike before, or any other bike with fuel injection

My K100 was unused for at least 3 years before I bought it and brought it home on a trailer.  I dumped out the old gas and added a few gallons of new fuel and a shot of Techron.  I cleaned the plugs and installed a new battery.  After cranking for a bit I finally got it to fire after turning the throttle back a ways.  It ran extremely rough as if it were only running on a couple cylinders.  I did a few start / run / stop cycles and it seemed to smooth out a wee bit, but would not idle. After shutting it off I took a small paintbrush, dipped it in water and used it to test the temperature of the header pipes.  Cylinders 1 & 2 hissed and steamed off immediately but #3 and #4 were cold. 

What's the next logical step here?  Is there a DIY approach for cleaning injectors that I should attempt?

Title: Re: Troubleshooting my barn find
Post by: Chaos on March 26, 2015, 10:20:55 PM

Plugs on 3 & 4 wet?  Check for spark, I think the K100 has 2 coils, may be able to switch them.  Could also try new plugs, cleaning doesn't always do the trick.

Title: Re: Troubleshooting my barn find
Post by: The Mighty Gryphon on March 26, 2015, 11:30:30 PM

Trace the plug wires for cylinders 3&4 back to the coil.  I think they both share the same coil and are fired together.  First thing is to check the primary wiring.  There might be a wire off.  I can't help much more than give moral support.  There should be someone more knowledgeable coming around to add more useful information.

Title: Re: Troubleshooting my barn find
Post by: RobP on March 27, 2015, 01:49:25 AM

Quote

Trace the plug wires for cylinders 3&4 back to the coil.

Bingo.  That was it.   

I had checked the HT wires at the plug ends earlier - and they were correct at those ends per the wire markers.   I pulled the coil cover off and compared the connections to instructions in my Haynes manual and found the PO had switched the HT leads across the coils. Refitted everything correctly and fired the beast right up and it ran great!

Thanks much!!

Title: Re: Troubleshooting my barn find
Post by: The Mighty Gryphon on March 27, 2015, 02:39:19 AM

 :clap:

Title: Re: Troubleshooting my barn find
Post by: richarddacat on March 27, 2015, 05:52:20 AM

Hope you have checked the air box too.

Good luck, sounds like you will be on top of it before long.

Title: Re: Troubleshooting my barn find
Post by: Chaos on March 27, 2015, 09:23:05 AM

PO's can be a bitch!

Title: Re: Troubleshooting my barn find
Post by: The Mighty Gryphon on March 27, 2015, 10:11:04 AM

Some of the best deals are on bikes that PO's messed up!

Title: Re: Troubleshooting my barn find
Post by: bocutter Ed on March 27, 2015, 12:39:17 PM

Yeah, my 250 'twingle' was $200.  :yes