Weak and sporratic spark on left side, HELP!!!

[PRoberts317]

My first post here, hope you can help!

I bought my first motorcycle at the start of this summer; a 1983 XS650 Heritage Special. The bike seems to be in pretty good shape, other than a few electrical problems.

The bike wouldnt run when I bought it, then I had the carbs cleaned and rebuilt it ran wonderfully. At this point the bike wouldnt hold a charge, I thought I needed to replace the regulator/rectifier, then found out I actually needed to replace the charging rotor, so I changed them both at the same time.

*Now on to the real problem*

So at this point the bike is running around town pretty good for about 10 miles, then I decide to take her out on the highway for the first time. I run on the highway for about 10 miles, then about a mile after I get off the highway the engine starts to misfire a bit. At first it only misfires between 2500-3500 rpm (in all gears, including Neutral), but if I keep it about 3500 or so I can ride fine, up through all the gears. This continues until eventually I cant get the bike to revany higher than 2500 or 3000 rpm (top speed is about 35 or 40mph at 3000 rpm in 5th gear). The decline in performance was gradual although very quick, but not immediate (maybe a connection shook loose or something??)

My first thought was that maybe some crap from the old (original) air cleaners got stuck in the carbs, so i take the carbs off, clean them out (nothing in there), and replace the airbox with pod filters. NO CHANGE.

I talk to a few old gear-heads, mechanics, and the usual lot... Most advice pointed to my ignition coils. I ordered performance coils from Mikes XS, and to help add to my peace of mind I also ordered new NGK performance plugs, plug caps, and plug wires... Hooked everything up, still no change... Sputtering and puffing sound from the left cylinder and out the back end of hte carb.

Checked out the resistance on the pickup coil (both wires are the same at about 770 ohms)
I graba timing light (I did mess with the timing plate a bit while I was exploring and replacing the alternator rotor), and when I hook the timing light up to the left-side spark plug wire the light fires sporratically and rarely, and furthermore I cant get the timing mark to come to where it's supposed to be. Then I hook the timing light up on the right-side plug wire and the light is firing away like its supposed to, but I still can't set the timing and I still cant figure out why my left side isn't firing correctly..



PLEASE HELP, IM DYING TO RIDE!!!

 

[Travis]

Might be the soldering connections in the TCI box..

Maybe try buying one on ebay and plugging it in to see if that's your problem.

What happens if you switch the spark plug leads or put the pickup sensor from the timing light on the right lead? Do you have 12 volts getting to the coil? If not, could be bad electrical connections or a bad a crappy ground somewhere.

 

[xjwmx]

It's not the tci box, since he says the right side is firing normally. Which means he should be able to set the timing by connecting to the right side wire. The problem is probably the plug wire end or the plug or less likely, the coil. Replace with old parts if you have them and see what happens. It all vibrates so much it might measure right when you measured it but be intermittent.

 

[Travis]

^^ good call. Guess I skimmed over that part.

 

[xjwmx]

We both skimmed over the part where he's already replaced all those parts with no change. Second impossible situation reported this week. The first was 14v on a good battery but it wasn't charging

 

[xjwmx]

Out of curiosity, clip the wires on the opposite plug, don't change anything else. Report back

If the prob doesn't go to the other side, it's the plug. If it does go to the other side, then switch the wires on the coil. If it goes back, it's the wires, if not it's the coil. If there's no change at all then the inaccuracy of your original discription qualifies you for a job as a TV news reporter.

 

[PRoberts317]

Thanks for the advice, but I dont think I made any progress today.

So here's where I stand today,

I switched the wires to the opposite plugs and I still have the same problem with spark; left side is weak and the bike wont reva about 2500. I by passed the entire electrical system by disconnecting the positive on the coils and ran a wire directly from the positive pole on the battery to the positive on the coil.... No change....

Any help would be awesome guys!!

 

[XSLeo]

It sounds like you have eliminated the ignition as a cause of the problem.
I might pull the carbs and clean them.
If you only got it at the start of this summer then you haven't ridden it much. Any crud from old or dirty gas in the tank will get into and plug the carbs. Depending on whats plugged it can cause your problems.

 

[pamcopete]

PR......,

I guess you're running two threads for this, so here's what I posted on the other one.

Unplug the reg/rect. Sometimes the magnetic rotor field will interfere with the TCI pickups.