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Still get no spark 81 GS750E

  • Thread starter Thread starter littlesuzyblue
  • Start date Start date
L

littlesuzyblue

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So, I've got this 81 GS750E which had no compression on the inboard cylinders when I got it. So I rebuilt the top end. Now it's got an Andrews G3 cam, vance and Hines 4-1 exhaust, Dynojet stage 3 carb kit, and a Wiseco 816CC big bore kit. I've replaced headset bearings, plug boots, petcock, battery, brake lite lens, handlebars, rebuilt the forks, front calipers and master cylinder, replaced the tires. I've ridden it once, briefly. So, I've got a bunch of money into this thing and now it won't start, seems I've got no spark. If I plug my meter into the coil leads at the ignitor box I get a resistance of 5 ohms to ground, when i ohm out the Hall sensors I get a resistance around 300 ohms well within the spec in the Clymer book. When I connect a AA battery to the hall sensor leads in the polarity specified in the Clymer book I get no spark, but if I reverse the polarity I get the sparks the way I should. I get around 10 volts at the ignitor box while cranking the starter. But still no spark at the plugs. Ocasionally I get a little spark at the plugs but almost never, and not enough to keep it running. I bought another used ignitor box but no luck there either.
 
no spark

no spark

make sure your coils are grounded good. they ground through the mounting bolts. Take them off and clean off all the paint ect..
 
Maybe this is obvious to you, but here goes:
Input current to the ignitor is OK, so what you want to test now is the OUTPUT.
There are wires that go from the ignitor to the coils (besides the wires that provide main power to the coils) to provide the "signal".
1. Connect a small test light bulb to each of the two wires (instead of the coils) and then ground the light bulbs so that a complete circuit is possible. As you crank the motor those two bulbs should flash (on and off) alternately. If they don't, then obviously your ignitor is not sending the signals to the coils. This means your ignitor is toast.
2. If everything is OK with step 1, then you need verify that you haven't messed up which wire is connected to which coil. But you're not getting any spark at all, so I suspect that there's no signal at all.

Usually coils fail one at a time and you're not getting spark anywhere, so it's most likely a bad ignitor, but I'd still check all wiring connections (grounds, etc.).
 
Last edited:
Oh, and of course, you must verify that your signal generator (on the crankshaft) is in fact sending the signal to the ignitor - a frayed wire is all it takes to mess that up.
 
the adventure comtinues

the adventure comtinues

So, I connected my meter to the frame and each of the crank trigger leads while cranking the starter and I get no voltage at either. so i pulled the harness and looked at it and I get continuity through the harness. So, then I pulled the timing cover and the magnet on the crank is very weak, how strong should this magnet be? Seems too weird to actually be the problem but, i don't know, maybe. Also, with the ignition on but not cranking should there be voltage at the coil leads out of the ignitor box? Or does that indicate an internal short in the coils?
 
littlesuzyblue said:
So, I connected my meter to the frame and each of the crank trigger leads while cranking the starter and I get no voltage at either. so i pulled the harness and looked at it and I get continuity through the harness. So, then I pulled the timing cover and the magnet on the crank is very weak, how strong should this magnet be? Seems too weird to actually be the problem but, i don't know, maybe. Also, with the ignition on but not cranking should there be voltage at the coil leads out of the ignitor box? Or does that indicate an internal short in the coils?
Click to expand...

OK, so you verified that those output wires from the "pulse generator" are NOT sending the signal - thus your problem. In this case, even with a perfect ignitor, you're not going to get spark.
Now, the magnet on the crank is not supposed to be VERY strong, so I wouldn't suspect that for now. It is more likely a loose or totally disconnected wire(s) somewhere (like maybe the "ground" wires for each pulse generator coil).
Also, there are TWO "hot" wires going to each coil. One always has current and the other is the signal current and goes on/off based on the pulse generator's signal to the ignitor.
 
Whoa, just re-read you post about checking the pulse generator. I think you did that wrong.
Neither of the two leads that come out of each pulse generator go to ground (on any bike I've seen). They both go to the ignitor (or "spark unit"). So when you were cranking the engine with the starter, you should have the multimeter attached to the two leads coming out of the same pulse generator coil!!
 
problems persist

problems persist

Well, I looked at that wiring diagram and it doesn't work for my bike, that one has 2 spark units and pulsers that have 2 leads. My bike has 1 ignitor box and each hall sensor has 1 lead that leaves it. That's why I plugged my meter into the sensor output in series. No voltage there. So, OK, someone said the magnet doesn't have to be very strong but what does that mean? Less magnet will mean less voltage. but how much magnet do I need? I touched this thing with the tip of a stubby #2 philips and I could only just barely feel it stick. I think maybe I'll pass a strong magnet by it and see if I get any volts. Anyway where is this "ground" wire on the sensors? I see only the blue and green wires which run to the box and a brown that connects them to each other. I'm gonna go look in a minute.
 
still ongoing research

still ongoing research

Well, I looked at that wiring diagram and it doesn't work for my bike, that one has 2 spark units and pulsers that have 2 leads. My bike has 1 ignitor box and each hall sensor has 1 lead that leaves it. That's why I plugged my meter into the sensor output in series. No voltage there. So, OK, someone said the magnet doesn't have to be very strong but what does that mean? Less magnet will mean less voltage. but how much magnet do I need. I touched this thing with the tip of a stubby #2 philips and I could only just barely feel it stick. I think maybe I'll pass a strong magnet by it and see if I get any volts. Anyway just came back in. There was some wrong thinking in how I was measuring the voltage, it seems that the pulsers have to be connected to the ignitor box to have a ground and thus have a voltage, It seems that since the pulsers have only 2 wires leaving them and one wire that connects them to each other that the ignitor box must perform some switching that enables each pulser to ground through the other in turn as the magnet comes around. So, reading the voltage with the meter paralelled to the leads in the connector I get .3-.4 volts while cranking, enough to produce an ocassional ragged spark until the battery starts to weaken slowing the spin of the crank. Any idea what I should be getting? I know Clymer uses 1.5 as the test voltage.
 
I don't think the pulse strength has to be very strong - just consistent. Of course the exact strength range will vary from bike to bike.
Now that you've verified that you consistently get signal from the pulse generators, then that changes the whole story. That means the signal IS in fact getting sent, and you've most likely been barking up the wrong tree. The problem is most likely somewhere down-stream from the pulse generator. Now test the OUTPUTS from the ignitor to the coils - Is that consistent too, or is it intermittent? I think you get the picture.

Weak/Intermittent spark can be due to many things:
1. The obvious: A too-weak battery on start-up. Also, once the bike is running a failing charging system will weaken the battery and lead to poor spark.
2. The somewhat-less-obvious: Bad spark plug wires and/or caps (you replaced just the caps).
3. The not-so-obvious - A gradually failing (partially functional) ignition component (coil, ignitor, pulse generator).

Items 2 & 3 above can be very hard to diagnose properly, because sometimes the "static" continuity test (for any of them) will show a good item, but when it is actually in service in the dynamic situation it will partially fail (this is often seen with coils and R/R especially - they pass static tests but fail intermittently when they heat up). Anyone working on bikes long enough has experienced this.

Sometimes the only way to figure it out decisively is to substitute with "known-good" components, one at a time. For example, if you put in a known-good ignitor and your problem goes away then you've found the culprit.
In your case, you don't know for a fact if ANY of the ignitors you've had on this bike were "known-good", so I suspect that first (but don't rule out the rest).
 
well

well

I was really looking for a more concrete diagnostic method, something that included more testing and less buying. Something I hadn't already thought of. Not that I don't appreciate the help, sometimes there really are no tests. Unless someone has parts to let me borrow, I'm buying, and well, since ebay and used parts won't satisfy the "known good" part of the equation that means new if even available, and since NOS parts add up to more than the Dyna set up if you can even find them. At the very least I end up buying a Dyna S, and/or a new set of coils and a wire set. But since this thing's a bit tweaked already the Dyna 2K is probably a better choice and that neccessitates new coils as well. Since this bike sits on a 1.25A tender, with a new battery, I doubt it's a weak battery problem, Since the leads are integral to the coils it doesn't matter whether it's coils or leads, the caps are new, so let's rule them out. But, since the coils fired consistently subbing a AA battery for the signals the coils/lead assembly and the connecting circuitry is most likely good, if they fail when hot I'll find that out later when I can get the thing running long enough to get hot. That leaves the pulsers, advance mechanism and the ignitor box in question. Since either Dyna replaces all these parts, I guess that's the way to go unless someone can pull a little magic out of somewhere, I guess that's all there is to do. Now I just need to decide how much I can spend, I guess. So anyone wanna tell me where I can get a good deal on a new ignition system?
 
littlesuzyblue said:
So anyone wanna tell me where I can get a good deal on a new ignition system?
Click to expand...

If you live anywhere near Spring Hill, FL 34606 you/re welcome to bring your bike over and swap known working parts off of mine to sort it out.

BTW this winter when I bought a brand new battery from AdvanceAuto I filled it with acid and charged it fully over nite and the second time I hit the starter it went virtually dead. Recharged it and it happened again. Took it back. I put the old battery back in and it worked better than the new one. Made in China!!! Isn't everything. At least the next one he gave me works okay...same brand.

Doug
 
I have an 82 750E, went through the same pain.

Screw that igniter mess and go Dyna....I havent had a spark problem since.

FWIW...
 
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