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weak power coming to spark plugs
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dustin.kerber
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PostPosted: April 16, 2006, 10:06 am    Post subject: weak power coming to spark plugs

I have a 1975 xs650b. I rebuilt the carbs this spring and installed a new coil on the left side (wasnt getting ANY power coming off of that side). Now, the system isnt putting off enough power to even creat a spark. I have managed to get a little spark if I use a screwdriver to gap the plug wire to the engine. I am getting nowhere enough juice to start it. I have a brand new charged battery, good points, and an intact fuse. I talked to the guy who had it last year and apparently he stuck a battery charger on it and put it on "start" to try to get it to start up (major amps). Do you figure that this damaged something in the electrical system, and if so, what? If it wasnt that, what is going on?
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grizld1
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PostPosted: April 16, 2006, 5:58 pm    Post subject: Re: weak power coming to spark plugs

You haven't mentioned plug wires, caps, or condensers. Wires and caps break down after a hundred years or so. You'll find a test for the condensers in your manual. They're both mounted in a single unit on your head stay and are hard-grounded to the frame by a ring connector which tends to corrode; the issue might be as simple as cleaning that ground contact thoroughly. If you suspect charging system damage, get a good multitester, one that has a 10 Ohm setting among the options, and work the steps in your manual.
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dustin.kerber
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PostPosted: April 30, 2006, 5:58 pm    Post subject: Re: weak power coming to spark plugs

Let's see here. I replaced the plug wires, caps and condensers. I have have traced along most of the ignition system with my multimeter and see I am getting 10.5 volts to the coils when the points are open and 8.5 to each as it's point closes. I know the problem is not with the battery or alternator, since I have hooked up a car battery with jumper cables and have had no luck.
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jayel
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PostPosted: April 30, 2006, 6:45 pm    Post subject: Re: weak power coming to spark plugs

what is the battery showing for voltage? voltage drops are caused by resistance - start at the battery with voltage reading and using wiring diagram go to switch (take reading) kill switch (take reading) ect. find where it's dropping the voltage
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Phred
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PostPosted: April 30, 2006, 9:29 pm    Post subject: Re: weak power coming to spark plugs

Never forget-new parts aren't always good parts! When troubleshooting, also check the new parts, when possible.
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dustin.kerber
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PostPosted: April 30, 2006, 9:54 pm    Post subject: Re: weak power coming to spark plugs

Jayel, thats what I thought, so I tested. The drop comes from the main switch(key). Going by the wiring diagram in the shop manual, the battery leads to the fuse and then leads off to the main switch, then the coil. From the coil you have your lead to the points and condensers, and your plug wire. The lead to the condensers and points are all good. I am showing about 0.1 ohms resistance scross closed points. I need to look at the diagram again, but I dont think that the kill switch is affecting the voltage.

Phred, that is what I am starting to think. The only question I have, is how do I test condensers? I imagine that I can check the coils off the list seeing as the old one and the new one both produce the same amount of spark. I have noticed that the new coil I bought of mikesxs.com gets warm after turning the bike over, while my old one doesn't.

I would also like to add a word of thanks for the advice. I am relatively new to repairing bikes, being 19, and with this my first bike I am really glad that there is a supportive community out there. Thanks guys!
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jayel
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PostPosted: May 1, 2006, 6:27 am    Post subject: Re: weak power coming to spark plugs

could be dirty switch, but did you you unplug the other wires to take them out of the equation? don't forget the ignition runs thur the kill switch also thats where i was losing my ignition
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dutch
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PostPosted: May 1, 2006, 9:22 am    Post subject: Re: weak power coming to spark plugs

Hey, a whole lot of electrical issues can be traced back to poor grounds. Check your battery cables and the other negative cable leading to your frame. On a bike that old, they are probably shot. On my 72 this was the case. Also, you may want to clean all of your wire and fuse box connections. Good luck.
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dustin.kerber
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PostPosted: May 1, 2006, 9:26 am    Post subject: Re: weak power coming to spark plugs

Thanks guys, in 2 weeks I will be out for summer vacation and go home. As soon as I get home, I will try working on connections, grounds, and kill switch.
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Phred
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PostPosted: May 1, 2006, 6:17 pm    Post subject: Re: weak power coming to spark plugs

Good suggestion about cleaning all the terminals. Might I also suggest using Truck-lite (not sure of the spelling-I seem to be out at the moment) on your connections. It is a grease made for coating battery and starter terminals, fusebox connections (wires and fuses can be coated), light and switch connections, etc. You just smear it on until the terminals are well coated, and it keeps water and oxygen off. Regular bearing grease would also work, but may be a bit messy. I am a mechanic, and we use the stuff on our fleet vehicles-it really works.

While on the subject of shop chemicals, "PB Blaster" is far and away the best penetrating oil I have ever found. Liquid wrench and WD-40 don't even compare. I highly recommend it!

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dustin.kerber
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PostPosted: May 15, 2006, 1:31 am    Post subject: Re: weak power coming to spark plugs

Well, another day and a lot more frustration passed. I spent the better part of the afternoon tightening and cleaning all the connections inside the headlight fixture.
My Haynes workshop manual has an wiring diagram in it that is supposed to be for the xs650 B, yet I am finding a lot of things that aren't right. For instance, the diagram shows the kill switch being on a blue wire coming from the main switch to the starter switch, YET in reality, the switch is on a brown lead that then goes to the coils. Does anyone know where I could get an ACCURATE wiring diagram?
I also spent a lot of time cleaning contacts with absolutely NO progress. I still have a spark so small that it can barely jump 1mm from a screwdriver.
I even went so far as to hook the damn thing up to a car via jumper cables to make sure that it wasn't a battery/alternator issue.
Any more ideas? Any hidden grounds? Replace wiring harness? Thanks for all your help guys... I appreciate it.
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dustin.kerber
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PostPosted: May 15, 2006, 2:12 am    Post subject: Re: weak power coming to spark plugs

As an afterthought, I snapped some pics of my bike. As you can see, the tank is off and it gets pretty dusty riding on the gravel rodes up here. Once I finally get everything going I will clean it up and post some pics.









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Wulf
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PostPosted: May 15, 2006, 5:10 pm    Post subject: Re: weak power coming to spark plugs

Hey Dustin, I seem to remember seeing a electrical schematic cd rom on 650 central.com that some guy came up with because most of the manuals out there have bad info on the wiring diagram. I'll see if I can find the link for it. You may want to consider checking the plug wires and spark plug boots for excessive resistance. I would think that you should have right at 12 volts at the coil so you probably have an excessive voltage drop somewhere.
Wulf

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Phred
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PostPosted: May 15, 2006, 6:23 pm    Post subject: Re: weak power coming to spark plugs

I agree with Wulf-there should be full battery voltage at the coil (within 0.1 volt or so)-anything less indicates dirty or loose connections. Also, bad grounds are *VERY* common culprits in vehicle electrical problems.
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Wulf
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PostPosted: May 15, 2006, 6:29 pm    Post subject: Re: weak power coming to spark plugs

Ok, I found the schematic page. www.650motorcycles.com...atics.html

Wulf

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Wulf
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PostPosted: May 15, 2006, 6:32 pm    Post subject: Re: weak power coming to spark plugs

Ok, I found the schematic page. www.650motorcycles.com...atics.html

Wulf

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dustin.kerber
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PostPosted: May 15, 2006, 8:43 pm    Post subject: Re: weak power coming to spark plugs

I have been using my multimeter to chech the voltage of the battery, and I notice that when I turn the key on, I immediately get a drop of ~0.7 volts. Is this a sign of a short somewhere along my system? Maybe in the wiring harness? Tomarrow I am going to begin by disconnecting different systems after the main switch to see if I can find where I am getting that drop. Thanks again for all the help guys. By the time I get done with this, I should be fairly familiar with this bike's system, at which point I hope to be an active member in this community. Thanks guys!
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kingwj
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PostPosted: May 16, 2006, 9:34 am    Post subject: Re: weak power coming to spark plugs

The voltage drop may be from power to the alternator as it is not a permanent magnet type and also the ignition system.
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dustin.kerber
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PostPosted: May 16, 2006, 11:52 am    Post subject: Re: weak power coming to spark plugs

So the drop is normal? Or is it not?
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dustin.kerber
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PostPosted: May 16, 2006, 2:21 pm    Post subject: Re: weak power coming to spark plugs

Just got done doing a few hours worth of teting with a multimeter.... Looks like grizld1 is right, the voltage drop is coming from the alternator. What is the deal? Should I be getting this drop from the alternator? The rest of the system looks fine, with the alternator connector unplugged I only get about a 0.08 volt drop when turning the key on (that is when both points are open). I feel as though I can almost see the light at the end of the tunnel.... What do you guys think about the alternator voltage drop?
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Wulf
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PostPosted: May 16, 2006, 5:39 pm    Post subject: Re: weak power coming to spark plugs

Just for general info, a voltage drop is caused by resistance to current flow. For instance, a length of wire by itself should have very little resistance. If you put one end of the wire on the positive post of your battery and the other end on the negative, you would have massive current flow because there is practically no resistance ( not to mention lots of heat and sparks too) If you added a light bulb to that length of wire you would see an increase in resistance, and voltage would be dropped across the load (light in this case ). If you add a switch in series to the wire and bulb you now have a way to controll current flow (on/off) and you will have also increased the resistance in the circuit as well. Each item in the circuit (ie. loads and connections) increase circuit resistance. As was stated earlier, most electrical problems are bad grounds which increase resistance, and thus decrease voltage. Never assume that because the bolt for a ground wire is fairly clean that the actual connection underneath is a good ground. When in doubt, clean the connection to bare metal if need be. One sure sign of excessive resistance at a connection is excessive heat so feel the connectors. If you get blistered, HEY!!!! There might be a problem there! Hope that gives you a little something to work on.
Wulf

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kingwj
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PostPosted: May 16, 2006, 6:11 pm    Post subject: Re: weak power coming to spark plugs

Check the manual, it has the resistance measurements for the stator and rotor. If you don't have a manual I would recommend you get one. The factory manual can be found at biker.net.

Just be glad we don't have lucas bullet connectors to worry about.
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dustin.kerber
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PostPosted: May 16, 2006, 7:12 pm    Post subject: Re: weak power coming to spark plugs

Wulf, I am sorry that I wasn't clear. I have been checking the votage at the coils. Since I should be getting full votage at my coils, I know something is wrong. I also notice that when testing the votage on my battery, as soon as I turn on the key I get a ~0.8 volt drop at the battery, even with the contacts open. Now, the current comes from the fuse, to the main switch, to the kill switch, and then to the coils. To make sure that this path was good, I tested resistance from the positive cable on the battery to the coil and found under 1 olm resistance; no problem here. I also tested and found no resistance from the coils to the motor when each point is closed. Knowing that this system was good, there had to be a something in the line that is causing a 0.8 volt drop along the whole system.

To test where the drop was coming from, I kept the multimeter on the coils and turned on the key (once again, points open). I then started unpluging parts of the electrical system until my voltage went back up to full. After a while of this testing, I found that unplugging the alternator connector caused the voltage to go back up to normal along the whole system.

My understanding from what you guys have helped me with is that I am supposed to be getting full voltage at my coils. So then this alternator is where the problem is right?

(also, I know it's not a weak battery, as I have hooked it up to a car with jumper cables and still had the problem)
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Phred
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PostPosted: May 17, 2006, 9:39 pm    Post subject: Re: weak power coming to spark plugs

Well, try starting the bike with the alternator unplugged (it will run quite a while on batt. alone)
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