78 gs750 ignition timing specs

[andrewclaycomb]

I am going to go pick up my new Dyna S and green 3 ohm coils in a few minutes, but I don't have a shop manual, so I don't know how to set the timing. I'm sure that the instructions will fill me in a little. I'm planning on pickup up a timing light today also, but I've never really messed with this kind of thing. Any good pieces of information from anybody with experience doing this on your 750?

Also I'm going to replace the plugs and wires. What should the gap be on a 78 gs750? Also the wires on it now are 8.8mm accel yellow wires. Will 8mm be enough? I think the previous owner used wires from his V8 mustang projects.

[andrewclaycomb]

already ran into a snag. What is the silver washer used for? Everything lines up fine without it, and it doesn't fit around anything. also do I keep the brass colored plate that was behind the points plate?

[dardoonk]

I think you are talking about the brass plate that has TDC marked on it.

I don't don't have Dyna ignition (yet), but somethings tells me your gonna want to keep that.

[andrewclaycomb]

Also when adjusting timing, what am I actually adjusting? The mechanical advancer, the dyna rotor, or the actual black boxes on the rotor?


When I took the gas tank off I confirmed that my petcock is bad, so that gets to be replaced as well. On a plus side, I discovered that the previous owner put accel coils in. I'm thinking about leaving those in and firing her up to see if the points/condensors were the problem and not the coils.

[jlderbycity]

timing

You will be adjusting the plate the ignition is attached to . It has three phillips screws. If you turn it to the right it will advance and to the left retard. I have the same setup on my 78 gs750. I personally run it almost fully advanced. It seems to run best that way. Also you can take one of the springs off on the mechanical advance and it will advance more quickly in the lowend which in return will give you better throttle response and midrange. The factory timing should be set at about 14 degrees, I set mine at about 24. Definately put the dyna coils on. Dyna ignition works best when it used together with other dyna components.

[andrewclaycomb]

and sudddenly it all makes sense. Where are the markings that show the degrees of advancement. When I took the old point plate out, it was fully advanced as well.


thank you thank you thank you

[t3rmin]

I'm sorry to be contrary, but absolutely DO NOT REMOVE THE MECHANICAL TIMING ADVANCE SPRINGS. The mechanical advance weights and springs are set up exactly how they are for a reason. They advance the timing at a certain rate and time in the RPM band which will give you the best performance and wear characteristics.

Also, do NOT simply adjust the timing by ear or run it "almost fully advanced". Use that timing light you bought and get it right. You will have poor power, gas mileage, plug life, and could possibly damage your motor over time if you do otherwise.

To install the Dyna S, just replace the old points plate with the Dyna S pickup coil plate. Leave the thin timing markings plate on there. It's not only needed so you can properly use the timing light, it helps the rotor align with the coils. I'm not sure about the silver washer, but if that came with the Dyna S it might be a spacer for the rotor. Be sure the little magnet on the rotor lines up perfectly with the pickup coils. Some models/years do need a spacer (mine does).

You adjust the timing by loosening the three retaining screws in the plate slots and rotating the plate one way or the other. Clamp the timing light on plug wire 1 or 4 and shine it through the hole in the top of the plate. On my 650, timing is 40 deg BTDC at full advance (several thousand RPMs to be safe), and 10 deg BTDC at idle, as I recall. (Please figure out the PROPER numbers for your 750 though, and use only the factory timing spec!) With my adjustable timing light, I just set the dial to 40, get the RPMs up, and make sure the mark for TDC lines up. Then turn the dial to 0, let the bike idle, and make sure the other mark lines up. That way you know the advance is working properly.

Timing really is critical, so please make sure it's done right. If I can clarify anything, just ask!

[andrewclaycomb]

Problems:

I have everything wired up. I didn't replace the accel coils with the Dyna coils yet because I didn't realize that I would need different wires. So I tried to just install the ignition. Everything went in smooth enough, still don't have an idea as to what the washer is for. If i put it anywhere on the shaft, the whole Dyna black sleeve will stick too far up and won't grab the machanical advancer. I'm hoping it's not required for this model of bike.

The problem is that the bike won't start. I tried adjusting the ignition while trying to start the bike just to get in the ball park but I didn't have any success. Any suggestions? I double checked my wiring and everything is secure, I even ditched the crimp on connectors and attached the wires directly but no luck. I'm guessing this is just a timing issue, but all suggestions are welcome. Once I get her running I have a timing light to use to fine tune.


Thanks for all the answers so far.

Also, how are you measuring degrees of advancement. When I look through the little opening I only see 2 lines, One is labeled F the other T. I also see 1-4 and 2-3 assuming those are reffering to cylinders

[t3rmin]

Problems:

I have everything wired up. I didn't replace the accel coils with the Dyna coils yet because I didn't realize that I would need different wires. So I tried to just install the ignition. Everything went in smooth enough, still don't have an idea as to what the washer is for. If i put it anywhere on the shaft, the whole Dyna black sleeve will stick too far up and won't grab the machanical advancer. I'm hoping it's not required for this model of bike.

If a spacer washer is needed, it would go on the outside of the shaft, not the inside where the rotor hooks to the weights. If the rotor has in-and-out slop on the shaft you need a spacer.

The problem is that the bike won't start. I tried adjusting the ignition while trying to start the bike just to get in the ball park but I didn't have any success. Any suggestions? I double checked my wiring and everything is secure, I even ditched the crimp on connectors and attached the wires directly but no luck. I'm guessing this is just a timing issue, but all suggestions are welcome. Once I get her running I have a timing light to use to fine tune.

Well first things first: are you getting spark? Hook a spare plug to one of the plug wires, ground it to the head, and crank the motor. See any spark? No? Try the other ones. If nothing's sparking then you haven't got the Dyna S hooked up right or your coils have no power.

If you have spark on all cyls and it's still not starting, and you're sure it's getting gas(!!!), then I suppose the timing must be radically off. Pull the Dyna S plate off and re-orient it (it's possible to put it in at three different angles of rotation). If you get anywhere in the ballpark with the timing, you should be able to get it started....

Also, how are you measuring degrees of advancement. When I look through the little opening I only see 2 lines, One is labeled F the other T. I also see 1-4 and 2-3 assuming those are reffering to cylinders

Check out this thread. Should tell you what you need to know:

http://www.thegsresources.com/_forum/showthread.php?t=99128

[KEITH KRAUSE]

If the bike won't start and you believe it's timing related...
The Dyna S paperwork should tell you how to "statically" (not running) set the timing. If not, you can statically set the timing and not even use a continuity light. Just use the spark from the plugs instead of a light going on. This will get you close enough for any starting purposes and then you can fine tune with a timing gun.
The "F" mark is for under 1,500 rpm's in most cases. No advance is involved yet. Basically, the F mark and the timing line above must align exactly at factory idle/not running.
The full timing advance line, is just ahead/right of, the "1-4" and the "2-3". These full timing advance marks must align with the timing line above when you are at approx' 2,500 rpm's and above (full advance).
To statically set using the F mark, remove ALL the plugs (turns easier) and ground plugs 3 and 4 to the head. Use the larger 19mm nut to crank the engine, not the smaller end bolt. Finger snug the small hex heads holding the Dyna sensors so you can easily move them when needed. Loosen/finger snug the 3 screws holding the mounting plate. Turn on the ignition. Slowly rotate the engine clockwise until you see/hear plug number 4 fire. Go slow enough that you stop right when you see/hear the plug fire. When it fires, the F mark for 1-4 should align with the timing mark above. If not, rotate the Dyna plate until it does. Snug up that sensor. Tighten the plate screws. Repeat for 2-3, but rotate the 2-3 sensor only to achieve exact spark timing, leaving the plate alone.
Now you can statically set the fully advanced timing.
Use the advance mark just ahead of 1-4. Ignition on, slowly rotate the engine while holding the advance rotor FULLY clockwise (full advance) with your thumb and index finger. Takes a little finger dexterity. The advance rotor holds the magnet that trips the sensors. When you see/hear number 4 plug fire, the 1-4 advance mark SHOULD align with the timing mark above, or at least close enough for starting purposes. Repeat to check advance for 2-3. Snug up the sensor screws. I always wait to fine tune the advance with a timing gun. More accurate than setting statically.
The bike should now start. Check with a timing gun once the bike is warmed up/idling OK. Unless your factory manual states otherwise, your gun should show the F marks align at approx' 1,200 rpm's and the advance marks align at 2,500 + rpm's. If the marks are off some, carefully adjust the sensors. If both F and advance marks don't want to stay lined up as a "set" at the different rpm's, be sure your mechanical advance is operating smoothly/lubed correctly. Weak springs can happen too. If the advance mechanism is operating correctly, the advance mark should line up exactly without compromising the F mark setting. If you have a little trouble, I always set the full advance mark exactly, even if it means the F mark setting changes a little. The advance mark is more important to set right. A little difference at the F mark setting generally is not noticable and older bikes may make it difficult to set the lower rpm timing just right.
PS: if you rotate the engine past the point where you see the plug fire, you don't have to go all the way around again to see when it fired, just back up a little and make another pass.
Also, once you set the sensors exactly and tighten (not too much) the hex heads, apply a dab of silicone to each side of each sensor body and let dry. The sensors will never move due to loosening screws or vibration.

[KEITH KRAUSE]

PS again: moving the sensor .01" = 1 degree change, according to Dyna.