Sudden, brief loss of power - 1987 K75C

[deilenberger]

Quick ignition switch test..

Turn ignition on (don't start the bike.)
Wiggle key. Don't turn it, just wiggle it in the on position.
If the dash/instrument lights flicker, your ignition switch needs disassembly and cleaning (you can't clean it without disassembly.)

[JamesInCA]

When my engine cutout , I instinctively ( ingrained spanish 2 stroke dirt bike reflex ) pulled in the clutch and coasted off the road . It immediately restarted at the side of the road and continued on ( for a while ) before it happened again . Ambient temp was 70s . My first failure was probably 25 miles from home, then failure 15 miles after that, then 10 miles after that , then 5 miles . The last time it didn't want to start immediately , though after sitting for a minute fired right back up as if nothing happened ! This was to be a 300 miles ride day and at that point I was spooked about it cutting out in traffic.

Since it was dry day and I suspected that it was heat related ignition failure since failures were becoming more frequent .... and I wanted to continue , I removed the T shaped cover over the Hall sensor to cool it off then kept on riding . It did fail again , but this time after 150 miles or in traffic and then restarted immediately. To me that pointed to a heat relationship to hall sensor. I replaced it with used unit and it hasn't hiccuped in the past 25,000 miles . Fixed !

Thanks, that's a very helpful description for what it could look like in a running context. I think I'll do a pre-emptive Hall sensor heat test, as it's still chilly here in SoCal, so even if the sensor is failing it might currently be getting enough ambient cooling to conceal that.

[075038]

I've solved this problem with NAPA "contact enhancer" CE-1, $70, aka Stabilant 22. The eye dropper bottle comes with "Q tips" to touch the posts and or the pinching finger tips of the computer connectors and others. The fluid will make a hissing sound as it cleans off the slow buildup of 15+ years of corrosion that also servers as a growing insulator. This stuff makes fuel injectors behave better when you touch their connector parts. It has helped numerous older fuel injected cars and bikes I've owned. I carry the bottle and Q tips to rallies in hopes of helping people like you. I've helped a few.

Sometimes just opening and closing a connector causes enough "rubbing" to clean off corrosion. Connectors are best designed if they wipe as plugged in and out. New parts installed also perform the wiping of the other connector, so the new part appears to have solved the problem when the old part with cleaner connectors would have been fine too. I also think many K bikes go for sale because the owner has trouble like yours and can't "trust" them anymore and then try some expensive troubleshooting . . . when clean connections could really make a big difference.

My 85 K100RS with 146,000 miles hasn't needed many parts, mostly just connector cleaning when trouble pops up. I have done several of the K bike tech page switch cleanings etc. as well.

Waiting a week or so for the bottle and spending $70 years ago felt bad, but since then using it has felt so good every time, many old Volvos, an old BMW 525i, several old K bikes, some old Chevy Suburbans. The fuel injection, computer and signal connectors are real low voltages so connector resistance can wreak havoc when beyond a decade old.

[JamesInCA]

Quick ignition switch test..

Turn ignition on (don't start the bike.)
Wiggle key. Don't turn it, just wiggle it in the on position.
If the dash/instrument lights flicker, your ignition switch needs disassembly and cleaning (you can't clean it without disassembly.)

It passes the wiggle test, thanks.

[JamesInCA]

I've solved this problem with NAPA "contact enhancer" CE-1, $70, aka Stabilant 22. The eye dropper bottle comes with "Q tips" to touch the posts and or the pinching finger tips of the computer connectors and others. The fluid will make a hissing sound as it cleans off the slow buildup of 15+ years of corrosion that also servers as a growing insulator. This stuff makes fuel injectors behave better when you touch their connector parts. It has helped numerous older fuel injected cars and bikes I've owned. I carry the bottle and Q tips to rallies in hopes of helping people like you. I've helped a few.

Sometimes just opening and closing a connector causes enough "rubbing" to clean off corrosion. Connectors are best designed if they wipe as plugged in and out. New parts installed also perform the wiping of the other connector, so the new part appears to have solved the problem when the old part with cleaner connectors would have been fine too. I also think many K bikes go for sale because the owner has trouble like yours and can't "trust" them anymore and then try some expensive troubleshooting . . . when clean connections could really make a big difference.

My 85 K100RS with 146,000 miles hasn't needed many parts, mostly just connector cleaning when trouble pops up. I have done several of the K bike tech page switch cleanings etc. as well.

Waiting a week or so for the bottle and spending $70 years ago felt bad, but since then using it has felt so good every time, many old Volvos, an old BMW 525i, several old K bikes, some old Chevy Suburbans. The fuel injection, computer and signal connectors are real low voltages so connector resistance can wreak havoc when beyond a decade old.

It's possible that cleaning the old connector might have done the trick, but I noted quite some time back that it's a mechanically unstable design in the first place. The male pins are held in place mainly by 25-year-old squishy rubber, and I've observed the action of closing the connector pushing them out of place. Replacing it with something more physically stable was already on the "when I get to it" maintenance list.

Just to reiterate, there's no evidence at this point that the problem remains unsolved. When it occurred, it happened several times in 60 miles. Since I've resumed riding after changing a few things, it hasn't happened in 600+ miles. I'm going with "solved" until otherwise indicated.

Oh, and I picked up a teensy bottle of Deoxit Gold at the local Fry's Electronics. It's marketed as a cleaner & contact enhancer like Stabilant 22 and has been used for this purpose for years by musicians. I intend to put it to the test on my dodgy tachometer.