Finish line in sight, but won't turn over!

[acr88_]

Hello all,

Nearing the completion of restorative work on my 81' GS750E. I replaced the entire wiring harness, entire charging system, rebuilt clutch (plates only), threw some Dyna coils on her (3 OHM) + NGK wires and caps, using OEM electronic starter, carbs have been cleaned/rebuilt entirely, jetted with S3 Dyno and pods and bench tuned, still using OEM exhaust system. However, I have been trying to get the thing to turn over for the last week. The starter motor just goes and goes until the battery is so drained it can't do much until it's charged, again. When I try to start on a full battery the most I can get is some popping sounds from the exhaust, and strangely, white smoke comes out of the carbs.

*EDIT: The bike was running before all of this service. Engine was healthy and I rode it for about 3 months as a daily. I then decided to fix everything. Inspecting all of it's systems revealed a lot of neglect from the previous owner.

So I did some diagnostics; checked if I got spark from all 4 wires (good), checked spark plugs (sparking), then checked if there was any compression by holding my thumb on each spark plug hole individually (while the others had their plug, then swapped to test the next one) and tried to crank and my thumb would be blown off. So I'm not sure where to check next at this point.

I have suspicions it's possibly fuel/air mixture? Or possibly the battery is just not good any longer?

Any advice is greatly appreciated.

Summers approaching and I have camping to do with her. Thanks!

[Nessism]

Does your bike have the leverless petcock? If so, the prime feature is most likely not working, and you are not getting fuel into the carbs. You can check this by removing the fuel drain screws on the float bowls. A goodly amount of fuel should come out.

[acr88_]

Does your bike have the leverless petcock? If so, the prime feature is most likely not working, and you are not getting fuel into the carbs. You can check this by removing the fuel drain screws on the float bowls. A goodly amount of fuel should come out.

Thank you for the fast reply. I was planning on checking that next, but I removed the pods last night and I saw fuel residue in the throat of each carb, but it really wasn't much. If I take the drain bolts out and not much fuel empties, what would this mean possibly? The petcock is failing? I believe I have the leverless petcock, its the OEM petcock, I've not replaced it yet, only cleaned it.

[KiwiAlfa156]

Check that the orientation of signal leads to the coils are correct (the coil pair are LH and RH - earth is common, but the coils fire alternately) and that the leads from each coil go to the correct plug. (1 and 4, 2 and 3). Popping and failure to fire if everything is working can be caused by this the sparkplug firing on the inlet stroke (the cause of the popping and smoke out the carb bell mouth), because the ignition timing is essentially 180° out.

[KiwiAlfa156]

Also, set the fuel tap to 'PRIME' this bypasses the vacuum operation of the tap and allows unhindered fuel flow. You can confirm fuel flow by removing one outside drain and turning the tap to PRIME to check fuel flow. Pretty sure that the 81 750E has the standard Suzuki 3-position tap, but may be the US models are different

[acr88_]

Check that the orientation of signal leads to the coils are correct (the coil pair are LH and RH - earth is common, but the coils fire alternately) and that the leads from each coil go to the correct plug. (1 and 4, 2 and 3). Popping and failure to fire if everything is working can be caused by this the sparkplug firing on the inlet stroke (the cause of the popping and smoke out the carb bell mouth), because the ignition timing is essentially 180° out.

Thank you kindly sir. I will check on that for sure. So you're saying the leads from the igniter go to specific coils? Did I misunderstand that part?

[rphillips]

Thinking out loud. Have you had the spark advancer off? The first GS eng. I completely took apart and put back together was 180 out. It's been 40 yrs ago, but I'm thinking I had installed the spark advancer (generator, assy. advance) backwards, I think I remember thinking why don't this thing have a dowell or key to insure it was right, but it didn't it will just slip on there correct or 180 out. I'm thinking all I did was just turn it around. Please, somebody correct me if I'm wrong about this thing going on either way... I'm pretty sure I just took it apart, turned it 180, and put it back together. I know I remember how excited I was to find my screw up so easy to get corrected.

[KiwiAlfa156]

Thank you kindly sir. I will check on that for sure. So you're saying the leads from the igniter go to specific coils? Did I misunderstand that part?

Yeah, if you look at the circuit diagram there are four wires that connect to the two coils. Orange/White trace are common and are essentially the earth/ground. The White and the Black are from the ignitor unit and these must connect to the coils with the correct plugs attached to them. White in the diagram goes to the coil that feeds cylinder 1 and 4, the black wire connects to the coil that feeds cylinder 2 and 3. If the coil has polarity on the spade connectors, then the O/W are -ve and the W and B connect to the +ve spade.

[acr88_]

Thinking out loud. Have you had the spark advancer off? The first GS eng. I completely took apart and put back together was 180 out. It's been 40 yrs ago, but I'm thinking I had installed the spark advancer (generator, assy. advance) backwards, I think I remember thinking why don't this thing have a dowell or key to insure it was right, but it didn't it will just slip on there correct or 180 out. I'm thinking all I did was just turn it around. Please, somebody correct me if I'm wrong about this thing going on either way... I'm pretty sure I just took it apart, turned it 180, and put it back together. I know I remember how excited I was to find my screw up so easy to get corrected.

I understand. Fortunately, I didn't take the spark advancer out at all. I only checked the condition of the housing gasket and the condition of the wires, being so old. I am curious about your theory, hmm.

[acr88_]

Yeah, if you look at the circuit diagram there are four wires that connect to the two coils. Orange/White trace are common and are essentially the earth/ground. The White and the Black are from the ignitor unit and these must connect to the coils with the correct plugs attached to them. White in the diagram goes to the coil that feeds cylinder 1 and 4, the black wire connects to the coil that feeds cylinder 2 and 3. If the coil has polarity on the spade connectors, then the O/W are -ve and the W and B connect to the +ve spade.

Nice. Great information thank you. I'll come back with an update. I for sure know I didn't check which wires went to which coil. I didn't know they had a designated coil and assumed it didn't really matter. I'm lucky if that ends up being the issue and we can move forward. She sounds like she wants to turn over, like tip of the tongue close, but something doesn't seem right, as I described.

[Nessism]

I'd try some starter fluid, or gasoline injected directly into the cylinders, to confirm whether the issue is spark or gas. My guess is gas.

[acr88_]

I'd try some starter fluid, or gasoline injected directly into the cylinders, to confirm whether the issue is spark or gas. My guess is gas.

Noted. And you mean spraying down the throat of each carb?

[Suzukian]

You should be able to turn the bike over and just spray the starting fluid, the carbs will suck it down. The coils go to specific wires.1 and 4 get one coil, and 2 and 4 get the other coil. You may have the set backwards.

[pdqford]

Just to describe the coil wiring another way:

The two O/W wires will have voltage when ever the ignition switch is “on”.

When the ignitor wants to energize the 1-4 coil it will provide a ground to the W wire.
This will cause current to begin flowing through the 1-4 coil primary circuit.
When the ignitor wants to fire the 1-4 coil it will release the W wire from ground.
This will cause the 1-4 coil primary field to collapse and induce a high voltage spark in that coils secondary field.

When the ignitor wants to energize the 2-3 coil it will provide a ground to the B wire.
This will cause current to begin flowing through the 2-3 coil primary circuit.
When the ignitor wants to fire the 2-3 coil it will release the B wire from ground.
This will cause the 2-3 coil primary field to collapse and induce a high voltage spark in that coils secondary field.

So the O/W wires can go to either coil.
But the W wire needs to go the 1-4 coil.
And the B wire needs to go the 2-3 coil.

[acr88_]

You should be able to turn the bike over and just spray the starting fluid, the carbs will suck it down. The coils go to specific wires.1 and 4 get one coil, and 2 and 4 get the other coil. You may have the set backwards.

That is encouraging to hear, thank you! Now I really can't wait to get off work and into the garage! lol.