Flywheel Magnetic Rotor Damaged

[Kentman7]

Hello. I have a 1982 Suzuki GS300L. The bike has about 1500 original miles on it.

After ALOT of work on this bike I finally got it running great last month. It was riding great!

Carbs have been cleaned and rebuilt, valve clearances done, no vacuum leaks, new cleaned and sealed gas tank, petcock filter is clean and working.

Then out of nowhere, my RPMs started fluctuating and the bike was bogging down when accelerating. Most notably, the bikes RPMs would randomly start to increase at idle when the throttle wasn’t engaged. The bikes RPMs will increase when the throttle is engaged as well, but, after a certain increase the bike will start to mis fire.

(In the past I had issues with the voltage regulator/rectifier. The RPMs would increase and decrease with the blinker as it was engaged. The RPMs would also increase when the high beams or brakes were engaged. I changed the voltage regulator and all was well after that.)

So I decided to change the voltage regulator again to a brand new one, instead of an extra one laying around. It didn’t work and we’re still experiencing the random RPM increase when the throttle is not engaged. I then opened the bike up to check the stator after some confusing multimeter tests. The stator looked great, no burn marks or anything unusual. I then noticed that the magnetic rotor that powers the stator had a chip in it. It’s probably a 1/2 inch long chip in the magnet portion. I remembered that I had damaged it trying to remove it to repair the starter clutch. I ended up just super glueing it back together. when I opened it up, it was still in place but loose to the touch.

So, my question is, do you think a chipped magnetic rotor would cause weird voltage issues causing the bikes RPMs to fluctuate randomly?

I have been getting good continuity tests on the stator as well as it looking in good physical condition. Continuity on the stator without the engine running was 0.5 on all wires. A continuity test on the stator while the engine was running was difficult due to the rpm fluctuations.

The battery tests showed it going up from 12.8 volts off to 13.2 volts at the idle, but wouldn’t go up past 13.5 when increasing the RPMs by the throttle.

any help is appreciated!

-Kent

 

[GregT]

I doubt if a chipped magnet would cause what you describe. Over the years I've opened up a lot of bikes and probably 50% of the time you'll find a chipped magnet.
If a segment as big as possibly 30% of the circumference is missing you'd notice the out of balance but I'd doubt if it would make a significant difference electrically.

 

[unfocused]

I ran into this problem with a later model GS500. The pilot jets needed changed. The lean mixture would cause the idle to increase unexpectedly and or randomly. After custom fitting ( hand drilled ) some jets to this motorcycle, the rider never complained again.

 

[bwringer]

That RPM fluctuation puts me in mind more of a lean condition, a vacuum leak and/or clogged/clogging pilots.

 

[Redman]

RPM increasing at idle is a sypmtom of intake air leak, maybe inlet boot cracked or the orings deteriated in the intake boots. I never really understood why an intake air leak increases the RPM (but weak power). AIr intake lead would reduce the fuel to air ratio and didnt seem like that would incread the RPM. Maybe its just that if sucking air thru intake boot, that is easier than having to suck air thru the carburator and allows engine to turn easier. But, anyway, Air intake leak is known to cause the idle RPMs to increase as engine warms up. IF adjust the idle stop when engine warm, then it will not idle when cold. Adjust idle stop when engine cold, then idle will run up higher when engine warm.

QUOTE
A continuity test on the stator while the engine was running was difficult due to the rpm fluctuations.
​EndQUOTE
No No, Dont do that. WHen engine running the stator is putting out voltage (AC voltage), and meter cant check continuity when meter is getting voltage put to it. (FOr meter to check continuity, it puts out DC volts, and monitors the current to determine the resistance. and so it gets messed up if something else interfering with that.)

WHat you want to check on the stator when engine running is AC volts. Should be about 60 or 70 Volts AC (meter on AC Volts) acrtoss any/all two wires. So three readings.
DOing this will give you good idea that stator windings are OKAY, and the rotor magnets are okay.