Looking for ideas... 81GS750EX

[PsychoRallye]

Hi all-

The bike was running great last year and would occasionally cut out while running and blow the ignition fuse. I finally found a short to the coil ground at one of the coils this year (after I did a bunch of other stuff, of course, sigh).

Over the winter, I replaced the regulator (the old one wasn't great) with an ElectroSport ESR100, the stator with an ElectroSport ESE100 stator, and the Ignitor and "points" with a Dyna S.

Great, new ignition system and electrical system! Well, other than the coils, the harness and the fuse box.

But, the bike just plain ole won't start.

There is spark on both cylinder banks
There is fuel (the carb bowls are wet anyway - i pulled the drain screw a little to see)
The starter is cranking just fine
The battery is reading decent anyway (maybe I'll just replace it to be sure)

Er...
Wha?

Suggestions on how to make sure that fuel is making it into the cylinder? Should the plugs be wet after cranking for a bit? (didn't pull a plug yet)

I plan on replacing the fuse box because the voltage drops to 10.5 or so across the fuse box. I guess 32 years was pretty good on the original.. but I don't think that's causing "the issue" here...

Also, I had to adjust the Dyna S quite a bit as I static timed it.. it is at the limit for the cyl1-4 adjustment, which seemed weird to me. Could that mean the spark is just at the wrong time? How could I screw that up? Anyone have a really good step by step on the timing? I don't see how I could have gotten it wrong...

Thanks
Justin

 

[posplayr]

I used to have an 1981 GS750EX and it was almost completely stock other than the few electroical tune up's I did to it. You should not have a drop down to 10.5V.

I would recommend removing opening up the fuse box and use some naval jelly to clean the corrosion and flow solder into the crimps.

Also make sure you have single point grounding. The Electrosport R/R should be OK but Time will tell. Its is still a shunt R/R.

The combination of poor graounding and the old style R/R resulted in this. Bruned ground wires

Just to get a quick baseline, do a simple test just do the Quick Test and report back your numbers.

 

[tom203]

After using "choke" (but no throttle input) and with a liitle cranking, spark plugs will at least be moist-smell them.
Double check your dyna wiring- remember that left coil fires #1 and #4- perhaps you mixed them up.

 

[posplayr]

Hi all-


Also, I had to adjust the Dyna S quite a bit as I static timed it.. it is at the limit for the cyl1-4 adjustment, which seemed weird to me. Could that mean the spark is just at the wrong time? How could I screw that up? Anyone have a really good step by step on the timing? I don't see how I could have gotten it wrong...

Thanks
Justin

The dyna pickups are set at the factory using little allen heads. Using a timing light you could adjust them instead of the entire plate.
The rear pickup fires 1-4 and the front fires 2-3

http://www.thegsresources.com/_forum/showthread.php?t=168652&highlight=ignition+timing

 

[PsychoRallye]

The dyna pickups are set at the factory using little allen heads. Using a timing light you could adjust them instead of the entire plate.
The rear pickup fires 1-4 and the front fires 2-3

http://www.thegsresources.com/_forum/showthread.php?t=168652&highlight=ignition+timing

OK so I think I did the timing right then, 1-4 is rear and 2-3 is the front. When doing the 1-4 per the Dyna instructions (first) - I needed to rotate the plate all the way (against the screws) and then also move the pickup itself (using the allen key) close to the end of it's adjustment range too... just seemed odd to me... should I be worried?

 

[posplayr]

OK so I think I did the timing right then, 1-4 is rear and 2-3 is the front. When doing the 1-4 per the Dyna instructions (first) - I needed to rotate the plate all the way (against the screws) and then also move the pickup itself (using the allen key) close to the end of it's adjustment range too... just seemed odd to me... should I be worried?

I remember having to be all the way on an adjustment but not sure if that was stock of dyna. remember you will also have to time the 2-3 if you moved the 1-4 pickup.

Other than using a degree wheel and an TDC engine stop (to confirm your timing mark) there is not much you can do other than to rely on the timing mark and time 1-4 and 2-3 independently if you moved the Allen screws.

If something is screwed up it would be the crankshaft and I have never heard of a twisted 16V 750 crank. Maybe RapidRay has heard of this.?,

 

[PsychoRallye]

I'll probably replace the battery .. 12.88 bike off, 12.02 bike not cranking but key/lights on (step 1 &2 on your list, can't get to 3-6 for obvious reasons )

Do you have a recommendation on a different regulator brand/model? I can always wire the ESR in as a backup and change to the one you recommend.. And yes, I have a single point ground (as much as you can on a bike anyway).

The regulator came with 3 yellow wires for outputs by the way.. can I assume those are all the same? It had no instructions...

I used to have an 1981 GS750EX and it was almost completely stock other than the few electroical tune up's I did to it. You should not have a drop down to 10.5V.

I would recommend removing opening up the fuse box and use some naval jelly to clean the corrosion and flow solder into the crimps.

Also make sure you have single point grounding. The Electrosport R/R should be OK but Time will tell. Its is still a shunt R/R.

The combination of poor graounding and the old style R/R resulted in this. Bruned ground wires

Just to get a quick baseline, do a simple test just do the Quick Test and report back your numbers.

 

[PsychoRallye]

I remember having to be all the way on an adjustment but not sure if that was stock of dyna. remember you will also have to time the 2-3 if you moved the 1-4 pickup.

Other than using a degree wheel and an TDC engine stop (to confirm your timing mark) there is not much you can do other than to rely on the timing mark and time 1-4 and 2-3 independently if you moved the Allen screws.

If something is screwed up it would be the crankshaft and I have never heard of a twisted 16V 750 crank. Maybe RapidRay has heard of this.?,

The engine was running fine before this electrical silliness and the crank looked good. RapidRay actually sold me my cams in the bike lol.

I did retime the 2-3 also because I moved the 1-4... but I will note that the advance didnt have any marks on the 2-3 side - only on the 1-4. That was a bit strange, but I measured as best I could for the 2-3 using 1-4 as a guide...

 

[posplayr]

The engine was running fine before this electrical silliness and the crank looked good. RapidRay actually sold me my cams in the bike lol.

I did retime the 2-3 also because I moved the 1-4... but I will note that the advance didnt have any marks on the 2-3 side - only on the 1-4. That was a bit strange, but I measured as best I could for the 2-3 using 1-4 as a guide...

The battery is dropping more than you would expect; generally about 0.5V. I would charge it a bit more and see if it doesn't get better.

Did you measure the voltage to the coils?

As far as regulators the Compufire is the best (but expensive at about $180). There is also an SH-775 ; both of these are Series R/R's. I just have not seen any data on the SH-775 while I did a pretty detailed set of tests on a Compufire.

 

[posplayr]

getting back to your problem of the bike not starting, I let mine sit just a little too long and my pilot jets plugged up. It only ran on 1 and 4 and 2 and 3 were completely plugged. Pull the carbs and remove the pilot jets. Then spray some carburetor cleaner through the p[ports. Run a small piece of soft wire through those pilot jets to make sure they are clear.

 

[PsychoRallye]

getting back to your problem of the bike not starting, I let mine sit just a little too long and my pilot jets plugged up. It only ran on 1 and 4 and 2 and 3 were completely plugged. Pull the carbs and remove the pilot jets. Then spray some carburetor cleaner through the p[ports. Run a small piece of soft wire through those pilot jets to make sure they are clear.

Just got it running... thanks. Carbs I'm guessing.. so I'll do just exactly as you describe, plus a new battery, and either fix or replace the fuse box so the voltage drop isn't so bad.

How can I tell if I got the Dyna S timing right when the bike is running? Just because it runs? Or more than that... timing light? (which I don't have). Or something else..?

Thanks
Justin

 

[PsychoRallye]

Oh, and the battery has been on the charger for days.. so It's gotta go.
Any suggestions on a battery that might last longer than 2 minutes on these things lol? I just replaced it about 1.5 years ago... no huge temperature extremes or anything (this is NY, not AZ)...

The battery is dropping more than you would expect; generally about 0.5V. I would charge it a bit more and see if it doesn't get better.

Did you measure the voltage to the coils?

As far as regulators the Compufire is the best (but expensive at about $180). There is also an SH-775 ; both of these are Series R/R's. I just have not seen any data on the SH-775 while I did a pretty detailed set of tests on a Compufire.

 

[posplayr]

Just got it running... thanks. Carbs I'm guessing.. so I'll do just exactly as you describe, plus a new battery, and either fix or replace the fuse box so the voltage drop isn't so bad.

How can I tell if I got the Dyna S timing right when the bike is running? Just because it runs? Or more than that... timing light? (which I don't have). Or something else..?

Thanks
Justin

The best thing is the timing light or you can static time it.

Move the engine to the low RPM mark, then rotate the ignition plate till you see the plug spark. If you practice a little you can get it within 1 degree.

You can do the same on the 2-3 if you can figure out when those are at TDC.