Bike Suddenly Broke Down

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MAW117

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Hi, my name's Michael; this is my first post. I bought a completely stock 1980 XS650 a few months ago for my first bike. Previous owner told me the engine was recently rebuilt. It's had been running fine and the bike would start first or second kick from cold (starter never worked great from cold). No pinging or any other weird noises or behaviors during those rides once I give the bike 10 mins or so to warm up. I've been putting 93 octane gas in it since I bought it.

Anyways, I rode around all day a few weeks ago. Rode about 60 miles of back roads taking stops every 30 minutes or so. Bike rode fine on the highway for about 20 miles at about 70 mph. Then, after I rode off the highway and into some traffic lights, my bike started to backfire and the power dropped significantly. Every time I had to stop, the harder it was to get the bike going again no matter how gingerly I controlled the clutch. Eventually, I couldn't get the bike going again and my friend carried it back to my place in the bed of his truck. I let my bike cool for a couple days and tried to start it up again. The bike would backfire and cut out under throttle just like it did while it was hot.

I dug around this forum but I am reluctant to dig into the carbs just yet, since I am not confident what problem(s) could have developed during that ride. Do you more knowledgeable people have any theories on what could've gone wrong? Thanks in advance.

-Michael
 
You can do a test by unplugging the rectifier/regulator. With it unplugged, start the engine and see how it runs.
If it runs normally, it means the small magnet on the alternator rotor has weakened. There is a simple fix.
 
it Sounds like the Varnish inside the carbs from setting a long time has decided to come off and plug all the tiny holes in the carbs
you could try draining the carbs but I doubt that will help.... what it needs is a good and through carb cleaning back firing is an indication of a lean condition too much air for too little fuel...... OR a timing/spark issue. my bet is carbs. there may well have been gasoline in the gas tank when it was stored for years and that evaporated away leaving a bunch of crud in the tank that will plug the carbs up....
so the entire fuel system should be cleaned tank, petcock, carburetors. Batteries are lucky to last a year or 2 on motorcycles , chances are it's needing replaced.... follow the carb section in the tech reference it's worth it's weight in gold !
and buy a can of WD40 and drown everything on that bike ! you won't hurt it doing that !
..... sorry to be the bearer of bad news but that is what I expect you need to do to get it going good again. get a manual and do reading in the Tech section before you tackle it !
good luck !
Bob.........
 
Welcome to the Forum, Michael.
If you gave us more background and data on the bike's history and condition, advice might be more forthcoming.
Did a shop do the rebuild, and when was that, etc.
Adding pics helps, too.
 
Um did the spark plugs go bad on you ? that is a constant possibility .. so you always carry extras with you !
could be just a plug dieing ! they act like that !
.....
Bob..........
 
The previous owner rode the bike last season. She got the engine rebuilt for preventative maintenance because she didn't want anything big to happen with the bike this season. She fully intended to ride the bike this season, which is why she had all this work done to it including new tires. The bike was in good running condition with only a little surface rust on the frame and exhaust. It was also garage kept while she had it. I am not sure about its life prior to the few years she had it, though. She got rid of it because she received a newer/nicer bike as a gift and no longer had a need for the XS. Bike has approximately 12,000 miles.

I replaced the spark plugs after I went to check on the bike a couple days after it broke down. The plugs I installed were BPR-7ES I believe (recommended per the Clymer Manual that I don't have on me), which replaced the BPR-6ES plugs that were installed with the bike I purchased. The old plugs were black with carbon deposits on them. The behavior of the bike didn't change much after I switched the plugs. The only other thing I have done to the bike is swap the uncomfortable special handlebars.

I don't think the battery is the problem, since the bike will idle.

Again, thanks for the help.
 
Sounds like the carbs need cleaned real good ! and checked !( float height etc,etc.)
...and those Idle air screws will need opening up sense the factory sets then at only 3/4 a turn out .... you gott'a drill out the stupid plugs over the idle air screws to get to them ( thanks EPA! ) but that's probably 90% of your problem right now !
.....
good luck !
.....
Bob.........
 
For some reason the human mind seems to be hardwired to blame the carburetors whenever the engine misbehaves. I've done it, the worst bumblers I've seen do it, some of the savviest wrenches I've known have done it. But you can't directly eyeball the A/F mixture the way you can read a multimeter, examine fuse contacts and connectors, or read a compression tester. So the first rule for identifying carb trouble? Check everything else first!
 
You're running resistor plugs, which you shouldn't be. There is already resistance built into the plug caps. Now you may have too much which could be giving you a weaker spark and that would explain the black plugs. Get the plain BP plugs, not the BPR.
 
retiredgentleman said:
You can do a test by unplugging the rectifier/regulator. With it unplugged, start the engine and see how it runs.
If it runs normally, it means the small magnet on the alternator rotor has weakened. There is a simple fix.
Click to expand...
Any weak magnet wouldn't happen suddenly. If it had weak magnet symptoms all of a sudden, I'd test the magnet pickup.

Re: carbs already off the bike, might as well go through them now since you should eventually anyway. Don't start wholesale replacement of parts, since the parts are all probably good and good new parts can be harder to scare up, for the unwary. You may have a leaking o-ring around the float valve seat, in which case replace only the o-ring for example.
 
Griz is Right again ! check everything you can first ! it's easier that way !
..... Bob........
 
For the 1980 to 1984 years, there are a couple of common problem areas that keep popping up.
1...............A weak magnet on the alternator rotor.
2.............. The old original, 4 position, fuse panel using glass fuses.

I suggest you eliminate these two potential problem areas, before chasing other less likely areas.
I already told you how to test for the weak magnet.
If your bike still has the original fuse panel, then its worn out, and must be replaced. Buy some automotive, in line blade type fuse holders, and install them (solder and heat shrink insulation).
 
I second the suggestion by RG regarding the fuse panel. After buying my '80, I inspected every electrical connection on the bike as a routine matter. The fuse panel looked OK upon visual inspection, but when I started manipulating the fuses, the prongs began to easily break off, one by one. Replacement with blade fuses was easy, one option is to use standard push-on crimp connectors (I solder them, as well). Then I tucked the whole bunch in a piece of old bicycle inner tube. Fits nicely in front of the battery.


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Last edited:
Yamadude:
Hay Nice ! great idea ! thanks for the idea ! I might be able to afford that mod !...... mine needs it !!!!!!!
......
Bob.......
 
Plus 1 for yamadudes response with one further step. Pair your circuit wires with a small band of heat shrink that way if you pull more than one fuse it isn't so hard to sort them out. That step would be before you install the female spades.
 
So you think a bad fuse connection could cause something like that. It just seems odd to me that a bad fuse connection would allow the bike to idle. Not that I am at all opposed to checking it out.
 

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