HELP! Intermittent power loss/poor idle&performance 77 GS550B + Dyna

[Chuck78]

I've just started to tackle this problem again after discovering that it was not a faulty dyna-s as a similar problem the same bike had 5 years ago.


77 GS550 runs pretty darn fine mist of the time for me with occasional acting up. For my wife, it acts up much more frequently.

when it acts up, it is almost as if it is running on 2 cylinders. Sometimes it seems that it clearly is, other times all for pipes are warm, but always overall engine sound is much different, sounds deeper and not healthy, no power, and when you go to give it throttle it dies out.
then all the sudden after shutting it off and restarting or sometimes just revving the engine after 5-10 minutes of poor running, it starts running fine.

Carb was overflowing after winter storage, cleaned/o-rings/rebuilt/new float needles. Bench synched.
Intake boot o-rings 5 years ago.
Valves adjusted.
Swapped a different Dyna s on. Same issues.
New spark plugs

Swapped entire coils plug wires Dyna s off good known running bike, fixed bad factory connection on coil power before running. Same issue still.

12.68 volts battery, 12.67 volts at dyna-s/coil power feed wire (bike off, can't recall if this was his test was when it was acting up or when it was running fine)

Put on Gunson Colortune clear spark plug when acting up.
Spark looked orangeish/whitish/purplish mostly. Ran poorly 10+ minutes. Revved it up and all of the sudden running fine. Spark looks purple-ish blue

Disected run/stop kill switch. Looked good, shot with contact cleaner.

Ignition switch died once all of the sudden 100% no working, 4+ yrs ago. Swapped used one way back when. It just went completely out when it failed.

Have gone thru harness many times fixing things cleaning connections etc. Everything in the bucket is pretty good.

Ohmed out white and black coil trigger wires to cois from Dyna S connection, .5 ohms and .6 ohms. My good running bike showed 1 ohms.

Charging system was working awesome, 14+ volts when revved up. Shindengen SH775 regulator rectifier installed since after the first road trip this problem showed up.




More in a minute.

Wife's trying to ride cross country, trying to depart today, pulling my hair out!!!! HELP!!!!

[Chuck78]

Have not checked bike voltage when problem occurs.

No fuse blowing. Wired via posplayr 's suggested rewiring power distribution method.

Have not torn into ignition switch. Has a shoei fairing on it as of 4am, more difficult now! 3 hours sleep...


Sooo..... Purplish spark when running good, when running horribly, orangeish whitish spark....


Do I have some elusive poor connection somewhere?????

Or a slight short to ground????


I'm about to run new coil power wires and coil trigger wires. Bike is running fine now tho, hard to tell if it fixed it without trial and waiting for failure!!!

[bonanzadave]

Swapped entire coils plug wires Dyna s off good known running bike

I see the wires and plug caps have been changed. Possible those caps are compromised ? I like to do the easy (cheap) stuff first. Run it in the dark to see if you can see arching from the caps, or just change them for GP. What is the coil voltage when its running ?

[Chuck78]

Okay...at DynaS 12v+ connection, I have very little voltage drop from battery voltage. Dyna connector wire is now spliced in and soldered and heat shrinked into the orange wiRe where one orange wire split off into 2 at a faulty eliminated connector, all 4 soldered together, source/2 coil feeds/Dyna feed.

NOW...

WHEN I PLUG DYNA S BACK IN, 10.2 VOLTS AT COIL 11.9 AT BATTERY!!!!
WITHOUT Dyna-S's load on the wire junction of the feeds to dyna-s and ignition coils, I have same voltage as battery. WITH DynaS 's load, 10.2 volts (BIKE OFF)
12.2 volts everywhere engine off kill/ign on Dyna unplugged new AGM battery slightly drained from all the troubleshooting.

Dirty ignition switch? Coil relay mod candidate???

[JTGS850GL]

Yes, you do still have some losses but 11.9V at the battery isn't so hot either. Besides a low battery, you may still have corrosion at the ignition and related harness connectors. Not uncommon to see melted connectors along the main harness.

[Chuck78]

Yes, you do still have some losses but 11.9V at the battery isn't so hot either. Besides a low battery, you may still have corrosion at the ignition and related harness connectors. Not uncommon to see melted connectors along the main harness.

Entire harness has been gone through numerous times and repaired/upgraded.
12.26v @ battery with everything off. Was 12.6v earlier but too much troubleshooting too little running to charge it since. 11.9v at battery bike not running, with ignition switch and kill switch on. No problems here, brand new battery, excellent connections, new regulator rectifier, 14 volts at mid RPMs when running.

no corroded connectors anywhere on this bike, everything has been gone through many times throughout the past six years. The only thing I have not looked at is internal to the ignition switch. I always crimp loose connectors or replace them, lube everything with silicone Dielectric grease.
I even went as far as to put silicone Dielectric grease on the coil terminals, tighten them down, wipe the excess off, then put RTV silicone sealant on top of them to waterproof them. New ignition switch connectirs, old one failed 2-3 yrs ago, corroded, brittle crumbling plastic

[Chuck78]

Ran back to my old house to move another load of shop stuff including a Bosch automotive relay and pigtail intended for a coil relay mod on my bike.

12v power at starter relay does not drop at all when ign+kill switches are on and Dyna is plugged in, whereas I lose 2 volts when the load of the Dyna s is put on that run of wiring looping through the ignition and kill switches and back into the harness to the coils and dyna... when the coils are charging/discharging running, I bet that 10.2 volts is far less even, scary!

Hope this does the trick.

Only positive of this aside from a more reliable bike is that my wife didn't gave to leave for a 9 hour ride in 31 degrees F, it's 44 degrees now! That Shoei FM2 fairing and winter riding gear will be very beneficial still! Ohio to Memphis, Mon Memphis to Austin TX. 12 days then TX to FL... Then back to OH....

[Chuck78]

What is the coil voltage when its running ?

Just checked before making coil relay mod and cleaning switch. 10.8volts running at 1 100 rpm

Should have done this mod a long time ago... or put in new OEM switches in all of our bikes. I'll send a spare with her and instruct her to order a new ignition switch from a dealer in Austin

[Chuck78]

600 miles so far last night and today, 120+ more to go today to Little Rock Arkansas. the bike has yet to act up on her! taking apart ignition switches to clean them, coil relay mods, or just replacing ignition switches is going to be another one of my mandatory procedures for any used GS or vintage motorcycle in general from now on

[60ratrod]

Dynas are really bad about causing vdc drops. Relay mods are about the only fix for that

[Chuck78]

Well she just proved that the coil relay mod fixed the voltage drop through the ignition switch, kill switch, and all associated extra lengths of wiring... 1,300 miles in 48 hours... Wow, she outdid me! Usually she yells at me when I want to ride mountain twisties for 7-9 hours a day on vacation (and then hike 3-5 hours in there somewhere)!

Only problem she had was a lower crankcase bolt started dripping oil. I guess that proved my justification wrong... I was in trouble for not yet starting to build her hot rod engine - 77 GS550 kicker bottom end with 1,800 mile transmission thrown in, clearanced to fit 650 cylinders, with 650 pistons and head, and BST33 Katana carbs. I wanted to wait for a group purchase for Wiseco custom run of K740 pistons to make it 740cc 10.25:1 instead of 673cc 9.4:1...

That and the headlight bulb must be acting up, bleeding a slight bit of voltage from the low beam filament into the high beam circuit, as her bright indicator LED which requires very little power to light up, keeps slowly starting to glow brightly.... To get the oil and neutral indicators to go out after killing the ignition switch, you have to throw the kill switch back into the on position to let the remaining tiny amount of electrons slowly feeding the LED's to get rapidly discharged into the ignition coils!