GT550 charges well when cold but stops charging when hot.

[Ebayru]

I have a 1974 GT550 with under 6000 miles on the odometer that I found in a scrap yard and have restored. It wasn't charging consistently and I discovered a toasted lead in the connector from the stator harness where it connects to the electric panel on the left side of the bike. I bypassed the bad connector wire and the charging system works perfectly UNTIL the engine unit gets hot. The battery is new and all the rectifier, regulator, stator and rotor readings are in spec, when cold. It has the Kokusan alternator and other components. I have an extra rectifier and regulator and swapping them out makes no difference. The brushes have plenty of length left and the rotor is clean. I have bypassed the regulator when hot and not charging and the stator output is low. When cold it is within specs for the Kokusan alternator. I have added a voltmeter to the bike so I can monitor the output. The accuracy of the voltmeter has been verified.

I'd sure appreciate any suggestions to help resolve the problem.

[oldjapanesebikes]

Sounds like you've got a good handle on most of what I would have suggested. The only other things I'd consider looking at is the harness itself, and also the fuse holder. The bullet style fuse holder originally fitted can cause lots of problems - usually if you can install one of the more modern cartridge styles in its place that would be best (IMHO). The harness wears where it rubs anywhere on the frame plus the connectors corrode badly - if you haven't already done so, I would take the tank off and then go through each main harness connector from the alternator to the headlamp bucket and starter button and clean the connections and then put them back together with some dielectic grease. The connector joining the two halves of the main harness has been known to over heat.

[Ebayru]

Sounds like you've got a good handle on most of what I would have suggested. The only other things I'd consider looking at is the harness itself, and also the fuse holder. The bullet style fuse holder originally fitted can cause lots of problems - usually if you can install one of the more modern cartridge styles in its place that would be best (IMHO). The harness wears where it rubs anywhere on the frame plus the connectors corrode badly - if you haven't already done so, I would take the tank off and then go through each main harness connector from the alternator to the headlamp bucket and starter button and clean the connections and then put them back together with some dielectic grease. The connector joining the two halves of the main harness has been known to over heat.

Thanks, Oldjapanesebikes.

I believe the problem was just as you stated. It dawned on me that my assumption that the engine temperature was a factor could be incorrect. I went back to the connector from the alternator to the connector board and took another look at the remaining blades within that connector and realized they were all in bad shape. I purchased another connector set and replaced that connector set. It seems that that may have been the problem. I haven't had a chance to put any time on the road with the bike as I just finished it and it's late. I probably won't get a chance to test it for a few days, actually. BTW, I replaced the fuse holder with the blade type before I ever had the bike running.

I'll post the results after I've had a chance to verify that replacing the connector solved the problem.

[rbond]

Not wanting to burst your bubble, but just to warn you. The problems also sounds like a charge coil on the stator is bad, that description is a classic example of coil failure. I hope that is not what the problem is, just giving a 'heads up'.

[Ebayru]

I finally had a chance to get out for a ride today and the battery is charging. Apparently, the stator/board connector was the culprit. I will check and clean the other connectors and use dielectric grease on them.

Thank you for that suggestion.

[Ebayru]

Rbond,

Thanks for your info regarding stator coil failure. Is there a relationship between running time or heat? I realize it's not easy to separate the two factors other than in cold weather riding, perhaps.

[rbond]

The culprit is heat. The wiring is very tightly wound in the coil, when a break occurs (factory defect in the wire it-self) the ends of the break are still touching. This still makes an electrical connection, so it still works. But as it heats from use and engine heat, everything expands very slightly, but enough at the break that the connection is lost. Sometimes the connection is barely there so you will get a lower reading with a meter than when it is cold. Then you may get closer to, or even the proper reading on the meter. If a coil is suspected, readings need to be done first when cold, then when it gets hot and quits working. If there is a big change in resistance, coil or even the connection to the coil is bad. If the readings are almost the same (within spec), coil is good, possible bad connection somewhere. Electrical problems can be both easy and almost impossible to fix.

[Ebayru]

Rbond,

Thanks for your excellent explanation. I'm sorry it took me so long to get back to the problem, but I was involved in a big project and had no available time.

Here's the latest: I ran the bike until the charging weakened to the point it would not produce more than 12 volts at about 4,500 rpm with the lights on. I then checked the stator resistances and much to my surprise, they were normal. I rechecked the rectifier and the regulator and everything is within specifications regarding resistances.

The only odd thing I've noticed, is when it is charging, my add on voltmeter tends to jump around as if the regulator is acting "sticky". The voltage will jump momentarily to over 15 volts, but then down to normal range. Also, the LED dial light on the meter, which is only on when the lights are on, flashes with the fluctuations. This tends to calm down after the bike runs for a while but then it gradually looses charge output. When the charging capacity is low, after the engine is hot, there is no more fluctuating or flashing of the gauge light. With the lights off, the output is obviously better and probably would keep the battery charged, but in our area I must run with the lights on.

I have another regulator which I swapped in just for the heck of it and it is the same. I purchased another stator, because I thought the problem probably was a bad wire (and the price was very good for a clean one), but have not installed it because the existing one checks out to be in spec, cold or hot.

I have changed to a 35/35 watt headlight bulb and a LED tail/brake light to lessen the lighting draw on the system.

Any thoughts or suggestions would be appreciated.

[Ebayru]

I forgot to state previously that the problem still existed, but to a much lesser extent, after I changed the connector to the electric panel. The charging was improved, but still degraded after running the engine for a while. I still worry about getting stranded if the battery voltage drops too low so I don't venture far from home.

I first realized I had the charging problem when I got stranded away from home. The bike is kept on a battery tender in the garage so I always start out with a full charge.

[oldjapanesebikes]

Grounds ?

[Ebayru]

Grounds as in bad grounds or leaking to ground? I have checked the ground connections before but I will take another look. I still haven't done anything with the dielectric grease on the connectors as I need to purchase some.

Are there any specifications as to how much draw there should be with the ignition on? I'm not referring to starting or running; just having the ignition on. I haven't quantified the draw, but there appears to be a significant draw just having the key in the on position with the lights off. I can not detect any battery draw with the ignition off.

[Craig380]

I've been running total loss on my 380 for a few years, due to charging issues.

On a fully-charged 9Ah battery I get around 2 hours riding (lights OFF), which is all I need from the bike anyway ...

[Coyote]

Is the heavy braided ground strap in place? The one that mounts on battery neg. to the engine through a bolt near the kicker. There is also a secondary ground (much lighter wire) that runs from the coil pack mounting bolt to the front center of the head shroud. Seems like more than 50% of electrical problems are due to poor grounds.
Also double check the tail light ground. That ground can really wreak havoc.

[oldjapanesebikes]

Grounds as in bad grounds or leaking to ground?

I was thinking of just grounds in general. Putting component failure aside (and one case of a chaffed wire harness) - the problems I've had generally fall into either bad connections (and I include bad in-line fuse holders in that category) or bad grounds. On a couple of my bikes, I've added in additional ground leads running from the original connection points back up to the battery lead just to eliminate any doubt.

[Ebayru]

I've checked all the grounds and connectors along the route to the termination of the ground. They all seem clean and sound.

I would think that the problem would lie within the charging circuits unless there is an increasing drain as the engine runs over time, heat related or not. I did not find any harness chaffing anywhere.

This is strange, but I'll keep thinking about it and rechecking.

Thanks for all the suggestions. I appreciate all of them.