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1985 GS700 lost all spark after turning off, replaced CDI still dead - please help!

  • Thread starter Thread starter oscaryu1
  • Start date Start date
O

oscaryu1

Guest
Hi there,

I helped my girlfriend buy a 1985 GS700 about a week ago. It had been sitting for a year or so, and needed carb work. I got the carbs all cleaned out and it ran like a champ after. I rode it 4 miles to her place (with the idle ever increasing, I assumed maybe a fuel line had been kinked and it was running lean or I needed to turn the idle down. Still made very good power). I turn it off, call her to show her, and wouldn't you know it it wouldn't start again!

Carb cleaner did nothing, and after pulling a plug and testing for spark I found none at all. I'm using the GS750 wiring diagram, but I'm getting ~11V to the ignition box (I've even jumped 12-13V directly to the box from a car, so voltage isn't an issue). I'm getting ~5ohms of resistance reading from both coils, each coil's orange wire (also feeding the ignition box) is getting power as well. I can get the plugs to spark by grounding out the coils by hand (which the ignition box is supposed to do).

Finally, I measured both pickup coils from the ignition box and they measured about 150ohms if I recall, both were very close to one another so I'm pretty sure that wasn't an issue. Thus, I ordered a used ignition box from eBay, replaced it, and STILL the same issue! No spark at all.

I'm at a loss now. I'm going to probe the ignition pickups with an oscilloscope hopefully later today but was hoping it wouldn't come to such a deep debug. Does anyone have any idea what I may be missing, or something I'm overlooking? :confused::confused::confused: The sensor gap wasn't touched, but look equal and not too far apart (a paper or two's thickness).

Thanks!

Oscar
 
83-86 GS750 Wiring Diagram.jpg

The wiring diagram I've been using for debug. At least with the ignition box, everything seems to match up (including the wire colors). The ignition box I bought to replace it was supposedly off a GSX750, but so was the original one that I found on there (so I have a feeling it's been replaced before).
 
Follow that orange/white wire the powers ignition coils this also feeds ignitor (it's not a cdi) thru a connector plug. Make sure ignitor box is seeing this 12 volt positive power- suspect and hope for just a bad connection . Buying used ignitors is an iffy business .
 
tom203 said:
Follow that orange/white wire the powers ignition coils this also feeds ignitor (it's not a cdi) thru a connector plug. Make sure ignitor box is seeing this 12 volt positive power- suspect and hope for just a bad connection . Buying used ignitors is an iffy business .
Click to expand...

Hey Tom! Thanks for the reply!

The ignitor box and both coils are seeing 12V. Well, 11V to be exact. I've even directly jumped 12V from a car into the igniter box to make sure it wasn't low voltage that was the issue, and to rule out grounding problems. Orange got 12V, black got ground. Still nothing.

I ran across this from searching the threads:

http://members.dslextreme.com/users/storagecliff/images/electrical_odd-n-ends.html#A11

This is for an '85 700 but you can probably use the same tests for your bike.

Here's how to check the ignitor. Remove spark plugs 1 & 2 and ground them to the motor so they will fire when they get power. With the ignitor facing you, the plug on the right side of the ignitor is where the signal generator plug fits. The two terminals on the right side of that portion of the ignitor will be pin 1 at the front and pin 2 at the back. The two left pins will be pin 3 in front and pin 4 at the back. Turn the ignition switch on. With a multitester set a the X1 ohm range put the + probe on pin 2 and the - probe on pin 1. Plug number 1 should fire. Next put the + probe on pin 4 and the - probe on pin 3. Plug number 2 should fire. If this happens the ignitor is good and the signal generators are suspect.
Click to expand...

I tried it and got no spark out of either igniter I have. I guess I got sold a dud. I'll scope out the trigger signals tonight, and grab some new plugs to rule that out (it's cheap, why not I guess). Kinda bummed but here's to hope.
 
Those 3rd generation 750's have a horrible reputation for frying ignitors. The spark advance is built into the ignitor so there is no easy solution regarding the fix other than gambling on a used ignitor. There are a few guys around with those bikes so you may want to put out feelers for someone to check your two ignitors on a known good bike because bench tests for ignitors has never been a reliable method of testing.
 
Another guy on here just recently opted for boyer bransden system (see link) to replace his failed ignition system on gs550 with similar ignitor box. Apparently it works with stock suzuki coils or you can opt for their coils . Hopefully, he will report back with a big smile! I have no idea what it costs, but since a girl is involved, think carefully

http://www.boyerbransden.com/pdf/KIT9091165.pdf
 
Nessism said:
Those 3rd generation 750's have a horrible reputation for frying ignitors. The spark advance is built into the ignitor so there is no easy solution regarding the fix other than gambling on a used ignitor. There are a few guys around with those bikes so you may want to put out feelers for someone to check your two ignitors on a known good bike because bench tests for ignitors has never been a reliable method of testing.
Click to expand...

Thanks! Would you happen to know of anyone in the northern California area? Or even possibly southern California? We're planning a trip down to LA next weekend and I'm sure we could reroute as necessary.

I did end up scoping the crank triggers, as pictured. They look like typical inductive crank sensors to me, one with larger voltage swing since it probably had a tighter gap than the other. Voltage measured at the igniter with ignition on, but still no grounding from the igniter outputs to the coil, and no spark.

The eBay seller almost immediately refunded me the cost of the igniter, so I get a feeling he didn't really test it. Let's hope to sourcing a good igniter somewhere.

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Hi I asked Boyer Branson if they had a kit for the Gs850x if it helps the reply is below

Thank you for your enquiry, the GS 550 to 1000 micro power kit should fit, check the plate holding the triggers has two or three mounting screws, two is the our gs1a stator plate and three is our Kh1a plate.
The micro power kit comes with two modern miniature dual output ignition coils, the old coils are not suitable for any of our kits.
The advanver unit is taken to pieces and only the centre with the timing marks is used.
If the machine has an electronic tacho it will require recalibration.
Contact us at sales@boyerbransden.com they can quote you including delivery, and supply the extra wires you require to connect the stator plate.


Regards Tech Dept.
 
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