'77 GS750 No Spark, Coil & Condenser Test

[McSkillet]

Greetings All,

I have been searching the GS forum for my answer and I'm getting bits and pieces from several post, but none seem to answer my question outright. If there is a post(s) that covers my topics in detail, please post the link and I will check it out.

I have acquired 2 '77 GS750's, 1 is assembled and is supposed to run and the other is a skeleton with all of the parts in boxes. After an oil change, the assembled bike ran erratically for a brief period of time after I first got it, and by brief I mean 10 minutes tops. When the bike was running, if I let off of the throttle the bike would die. My research told me that since the bike had sat up for such a long period of time (1yr+) I should do an extensive carb cleaning. So I did. Each carb soaked for 24+ hrs and received a new O-ring kit. Intake boots too. Well, the bike was still a no go. I decided to checkout the points and condensers. They appeared to be like new. I tried starting the bike to see if the points sparked any, and they were not. So now I get to my question. Do I test the condensers while they are installed on the bike or off of the bike? I tested them off, but did not get a reading. From my understaning the ohm meter should go up to infinite ohms then start to fall gradually. The ohm meter was set at 200 max ohms.
Then I tested the coils. My first test was to see if there was any spark at the plug. With the plug out of the cylinder head and grounded to the head I tried starting the bike. There wasn't any spark being delivered to the plugs, all 4. So my next test was to see if there was any voltage at the orange/white wires going to the coils. There was 12+v to each. There was contuity from the points to the black & white wire at each coil. I measured the primamry resistance for each coil, one @ 5.0 and one @ 5.4 ohms. Both OK. When testing the secondary resistance for the coils I got 20k+ ohms for about 2 seconds and that was the only and last reading I've gotten from either coil. I tested the coils by measuring the resistance form plug wire to plug wire, is that right or wrong? Either way, I didn't get anything when testing from any of the other wires. My guess is the coils are original, but I can't say for certain since the guy I bought the bikes from did a tiny bit of work to it before storing it.
I went ahead and bought a Dyna S ignition setup to replace the whole ignition, but wanted to see if there's something else that I can test to see why I'm not getting any spark.
I've also tested the neutral switch, it functions properly.
I'm not sure how to bypass the kill switch to see if that is my problem. Add that to my list of questions that I could use an answer for.
Any help on these items will be greatly appreciated.

Rgds,
Jeff

 

[Steve]

Let me see how many of these issues I can address:

I have been searching the GS forum for my answer and I'm getting bits and pieces from several post, but none seem to answer my question outright. If there is a post(s) that covers my topics in detail, please post the link and I will check it out.

I have acquired 2 '77 GS750's, 1 is assembled and is supposed to run and the other is a skeleton with all of the parts in boxes. After an oil change, the assembled bike ran erratically for a brief period of time after I first got it, and by brief I mean 10 minutes tops. When the bike was running, if I let off of the throttle the bike would die. My research told me that since the bike had sat up for such a long period of time (1yr+) I should do an extensive carb cleaning. So I did. Each carb soaked for 24+ hrs and received a new O-ring kit. Intake boots too.
So far, it sounds like you are on the right track.

Well, the bike was still a no go. I decided to checkout the points and condensers. They appeared to be like new. I tried starting the bike to see if the points sparked any, and they were not. So now I get to my question. Do I test the condensers while they are installed on the bike or off of the bike? I tested them off, but did not get a reading. From my understaning the ohm meter should go up to infinite ohms then start to fall gradually. The ohm meter was set at 200 max ohms.
I take it you are using an analog meter? Set it to a higher range, like 20k. If the needle moves, then slows down and stops, reverse the leads to see if it does it again. If so, it's good.

Then I tested the coils. My first test was to see if there was any spark at the plug. With the plug out of the cylinder head and grounded to the head I tried starting the bike. There wasn't any spark being delivered to the plugs, all 4. So my next test was to see if there was any voltage at the orange/white wires going to the coils. There was 12+v to each.
Again, sounds good. 12+ volts at the coils is always a welcome sight.

There was contuity from the points to the black & white wire at each coil. I measured the primamry resistance for each coil, one @ 5.0 and one @ 5.4 ohms. Both OK.
Still looking good. Not sure about actual specs, but in the vicinity of 5 ohms is good.

When testing the secondary resistance for the coils I got 20k+ ohms for about 2 seconds and that was the only and last reading I've gotten from either coil. I tested the coils by measuring the resistance form plug wire to plug wire, is that right or wrong?
Plug wire to plug wire is the only way to measure the secondary side of the coils.

Either way, I didn't get anything when testing from any of the other wires.
None of the other wires should show continuity to either of the plug wires.

My guess is the coils are original, but I can't say for certain since the guy I bought the bikes from did a tiny bit of work to it before storing it.
I went ahead and bought a Dyna S ignition setup to replace the whole ignition, but wanted to see if there's something else that I can test to see why I'm not getting any spark.
I've also tested the neutral switch, it functions properly.
I'm not sure how to bypass the kill switch to see if that is my problem.
If you are seeing 12 volts at the orange wire on the coils, flip your kill switch to see it go to 0 volts. Flip it back to see 12 volts again. There is no need to bypass the switch.

Add that to my list of questions that I could use an answer for.
Any help on these items will be greatly appreciated.

 

[almarconi]

My first suggestion would be to get a service manual. In order for the bike to run you need spark, fuel and air at the proper time and in the correct amounts. When you get the service manual go through and check each system (charging, ignition, fuel..etc) to make sure they are working properly. A bike that old more than likely will have some electrical issues to deal with. You might have a faulty ground somewhere and not get a spark.
Go here

http://members.dslextreme.com/users/bikecliff/

and download a service manual for your bike.

It is near impossible to try and diagnose your problems without knowing a much more detailed maintenance history on your bike. Your off to a good start by cleaning the carbs and changing the oil. There is lots more that needs to be done such as valve adjustment, checking the charging system, ignition system, electrical system, cleaning fuel tank..etc. Until you have done the basic maintenance it is difficult to diagnose your problem. Ignition problems can appear to be fuel delivery problems and vice-versa, until you've gone through and checked each system it will be very difficult to troubleshoot. Be patient, take your time and ask questions as you go along.

 

[McSkillet]

Well, it's great to know that I'm headed down the right path, so far. It will probably be this weekend before I get to tinker with the bike again, but I figured I needed to give a few missing details to the replies that I have received (thank you). I have both the Clymer and shop manual for the bike, and surprisingly the Clymer offers decent details. The Clymer I have for the 3rd bike (v65 Magna) I acquired leaves a lot to the imagination.
I did test the kill switch at the orange/white wires and it does interrupt the voltage. So that means good? The wiring harness also appears to be one of the items replaced because the wires & harnesses look brand new. So, I guess it's down to tracing a short or bad ground in the ignition portion before I install the Dyna.
Thanks again for the feedback and I'll keep you updated as to what I find, or don't find.

Jeff

 

[SqDancerLynn1]

block the points open and check for 12V at the points

 

[McSkillet]

Assuming I did this correctly, I have 12.07 volts @ each point. The way I tested was to place a piece of paper between each point contact, directly connected the orange/white wires to the black & white wires, then using a volt/ohm meter, I placed the red lead on the terminal where the condenser lead attaches and the black lead of the meter was grounded to the engine block. If I've goofed up this test, let me know.
Otherwise, what does this test prove?
Oh, and to respond to part of Steve's question concerning the use of an analog to test the condensers. Yes, I have both types of meters. I'll retry the measurement again at the 20k setting.

 

[McSkillet]

The Dynatek kit solved my problem. Once I deciphered the instructions on how to statically time the bike, it fired right up on the second press of the starter button.
If I had to guess where the real problem was, it would have been with the coils. I know that's supposed to be a rarity, but after retesting the coils, P&C using the advice given, the secondary side of the coils were the only items to not pass.
Now all I need to do is fine tune the carbs...
Thanks to all that contributed to my Q&A.

Jeff