GS850G Won't Start, Electrical Issue, No Spark

[chuck hahn]

does the end of the crank have the pin that engages on the back of the mechanical unit? Im thinking it does and it engages the stock rotor. Im no expert on mechanical advances but i would have to think they are all the same. To me from a manufacturers standpoint it doesnt make sense to have different ones. Just make it a one size fits all to cut down on costs.

[chuck hahn]

I think theyre all the same. Hell try this one. If not resell it or return it....add says 30 days return policy

NOS Genuine Suzuki Advance Governor Assembly GS750 GS 750 1977 1979 33120-45020 | eBay

[chuck hahn]

27 dollars with 30 day returns....

1978 SP370 SPARK ADVANCE GOVERNOR ASSEMBLY SUZUKI SP 370 1978-1979 33120-32410 | eBay

[dandypop]

That's fair. The part number differs only slightly (33120-45110 is the original, while 33120-45020 is the $40 one you sent). The $27 one looks a little different.

[chuck hahn]

One thing Suzuki did that others didnt do was change part numbers on the very identical part from model years. Like say in 82 it was XXXXX-12345 then in 83 they made it XXXXX-12346. Same identical part but 1 number off where as others used the same number through many years until that particular part actually had a change then they gave it the updated number. no harm in giving these a shot.

[dandypop]

I've got one on the way! It's originally the part # for an '81GS1100E (part #33120-49211). I'll resell it as you suggest if it doesn't work. Thanks!

[KiwiAlfa156]

There was a lot of parts sharing between models. The CMSNL website is great as it shows all the models that exact part was used on.


Some parts do get superseded and are issued a new number. But they always follow the same part code format:




With the ATU units, as far as I know, externally they are the same and they can all be swapped. Where they vary is in the initial and full advance ignition timing and the number of degrees advance. This is controlled by spring tension and the metal stops within the unit. A troll through the spec sheets will show that different model GS have differing ignition timing especially at full advance because burn speed is a function of combustion chamber design (swirl and squish) and diameter.

I had indexed the ignition markers during the build as I had to repair the ATU locating pin on the crank. Good thing I did as it was about 3° to 4° retarded which is a lot in ignition timing term.




I had been really disappointed with the bikes acceleration given the work I had done on the engine. Searching for the reason, I found the ATU unit that was fitted to my 750 didn't advance all the way to the full alignment (above 2,750 rpm), when set at the idle mark alignment. It dawned on me, that the ATU was off another bike (this machine was essentially a rolling wreck when I bought it).

I have since set the timing to align at the full advance mark, so at idle the timing is a couple of degrees advanced due to the short advance sweep. The only downside is that it cranks sluggishly as at starter rpm, the early spark means she's compressing more expanding burning mixture. Once she's going its all normal from idle, has really useful mid-range and screams above 7,000 rpm.

[chuck hahn]

KIWI..
So based on your pics lets just say the one e bought is off a bit. Lets say he rolls it to TDC as close as he can get using a screwdriver to watch piston travel and stops the instant the screwdriver stops. Then notes the T mark is off by 1 mm to the left of the case pointer.
My thought would be scribe a new mark on the advance governor and a new mark the same distance from the F mark. Theoretically this would provide new good marks for finding TDC and strobe timing. May not be to factory spec but it should be very close with the new set marks added. Whats you thought?

[salty_monk]

Pretty common that an overcharging event like this would fry the igniter..... Headlight bulb blowing is usually the first obvious sign.

[KiwiAlfa156]

KIWI..
So based on your pics lets just say the one e bought is off a bit. Lets say he rolls it to TDC as close as he can get using a screwdriver to watch piston travel and stops the instant the screwdriver stops. Then notes the T mark is off by 1 mm to the left of the case pointer.
My thought would be scribe a new mark on the advance governor and a new mark the same distance from the F mark. Theoretically this would provide new good marks for finding TDC and strobe timing. May not be to factory spec but it should be very close with the new set marks added. Whats you thought?

Hey Chuck, the problem with using a screw driver is that as the crank rotation passes over the TDC 'hump', piston travel per degree of rotation is exponentially smaller increments to the point the piston stops and reverses travel. And finding the point of travel reversal with any accuracy only works with a dial gauge. You can see the exact point of reversal on the dial (which you can repeat), and last degree or two of rotation might yield only a fraction of a thou of movement either side of TDC. The other method is to use a positive stop and a degree wheel to locate TDC.

I guess its all about locking down TDC as a known datum, as you are setting everything else off that. How you mark that is up to you. The problem I had was the index pin on the end on the crank had been sheared off by the PO (who knows how?), and who stuck the ATU assembly back in place using a wood screw buried in what looked like a generous helping of JB Weld.



I had to grind out the remains of the pin with a diamond burr and fashioned a new pin out off a 4 mm drill shank. It worked, but i couldn't really be sure the index pin was in the exact position (there was a little bit of play). Hence checking whether the T mark aligned with the pointer correctly indicating TDC... It didn't.



If the crank index pin and the ATU is unmolested, There's a 99% chance it will all bolt up within tolerance. Once the ATU is torqued down on the crank, the relationship between the static pointer and the "T" mark is fixed The only adjustable variable from that point is to advance or retard the spark timing by moving the pickup backing plate. All timing is ignition important, but ignition timing at full advance is the most important. Because spark timing is fixed from around 2,500/3,000 rpm to redline and that's where you spend most of you time, under that the engine is basically at idle.

The torque producing expansion of the heated gas pushing on the piston has to extracted in about 80° out of 720° of total crank rotation. Timing peak pressure is how we extract maximum torque from combustion. So you can loose ponies by having the timing a little wrong.

[chuck hahn]

Kiwi..
I get what youre saying. And i imagine position of the T would vary based on stroke length as well. My idea was first to find TDC ( relatively close ) with a screwdriver then view the T mark to see if its close to the timing mark. At least this would give some assurance that possibly the F mark would be at least trustable when timing lights used.
Not everyone has dial guage to be exact so you gotta do the best given the situation. If it was me and the T mark was there or just touching the mark id just time it as normal. If it was off a tad one way or the other i would apply the same amount to the F mark before timing.. follow me ??

[Grimly]

Absence of a dial gauge, just bring it up to TDC either by eyeball, screwdriver, modified spark plug, etc, and rock it back and forth by the same number of degrees either side. In the middle of that is TDC, good enough for government work.

[KiwiAlfa156]

Absence of a dial gauge, just bring it up to TDC either by eyeball, screwdriver, modified spark plug, etc, and rock it back and forth by the same number of degrees either side. In the middle of that is TDC, good enough for government work.

Yep, definitely works as a sanity check

[KiwiAlfa156]

Kiwi..
I get what youre saying. And i imagine position of the T would vary based on stroke length as well. My idea was first to find TDC ( relatively close ) with a screwdriver then view the T mark to see if its close to the timing mark. At least this would give some assurance that possibly the F mark would be at least trustable when timing lights used.
Not everyone has dial guage to be exact so you gotta do the best given the situation. If it was me and the T mark was there or just touching the mark id just time it as normal. If it was off a tad one way or the other i would apply the same amount to the F mark before timing.. follow me ??

Yes, the timing marks from the factory are good to go. Checking TDC by the screwdriver method or otherwise is only really something to look at if you've replaced or repaired something under the cover, or are unsure what a PO has done. Fix what's broken, not what's working.