Engine Ignition Timing question

[GS750GUY]

I did a search in the technical forum and could not find an answer to my specific question regarding the engine timing on my 78 GS750EC.

According to my service manual the instructions for checking and adjusting the ignition timing reads as follows: "After removing the contact breaker cover apply a socket wrench to the hexagon nut and rotate the engine in a forward direction while viewing the ATU through the inspection apeture in the contact breaker stator plate. It will be seen that there are three scribed lines on each side of the ATU".

It says to rotate the engine until the F1-4 mark on the ATU is in exact alignment with the index pointer mark on the plate fitted to the rear of the stator plate".

My question is this: I am seeing three scribed lines on the plate but I am not sure which scribed line I am supposed to line up with the index pointer line. The three scribed lines I am seeing through the apeture look like the following: I have indicate these lines in red below. I am guessing it is the middle red line that I need to line up with the index pointer line but the manual instructions are not real clear.

l T l F1-4 l


I appreciate your help with this!

Thanks, GS750GUY

 

[GregT]

The line to the left of the "T" is top dead center.
The next line to the right is firing point when fully retarded - ie the timing mark at which the points break when doing a static setup.
The final mark to the right is full advance.
Check timing with a timing light when the light should show timing at idle to occur at the middle line and move to the right hand line as the revs increase.

Hope this helps

Greg T

 

[GS750GUY]

The line to the left of the "T" is top dead center.
The next line to the right is firing point when fully retarded - ie the timing mark at which the points break when doing a static setup.
The final mark to the right is full advance.
Check timing with a timing light when the light should show timing at idle to occur at the middle line and move to the right hand line as the revs increase.

Hope this helps

Greg T

Thanks for your help, I thought I was correct in that it is the center hash line that I needed to use for determining the proper time the points began to open for cylinders 1-4.

Another thing though:

I noticed that when I used this center line to set the timing for the 1-4 cylinders that I now have the outer main adjustment plate turned completely to the far left as far as the three plate hold down screws will allow it to move. And even in this far left position the 1-4 points are still breaking just slightly to the right of the center hash mark. I need the adjuster plate to move further to the left to break the points just over the center hash line but I cannot move it any further.

I notice in the manual photo that the top center hold down screw seems to be pretty much centered in the elongated adjuster plate hole, where the same screw on my bike is clear to the left of the elongated slot when the points are breaking near the center hash mark.

Do I have an adjustment out of whack somewhere?

GS750GUY

 

[SqDancerLynn1]

USE the left mark if you are adjusting with the engine OFF center is timing at idle. Last mark is full advance --above 2500 rpm

 

[GS750GUY]

Ok guys........I'm starting to get kind of confused now. GregT said to use the center line when doing a static set up and the other said to use the far left Top dead center line if adjusting the timeing with the engine off.

I'm not using a conventional timing light but a 12V bulb with two wires and alligator clips attached like described in the manual instructions below.

I have typed below exactly how my service manual reads:

"Commence ignition timing checking on the left-handed contact breaker set, which controls cylinders #1 and 4. To determine at which moment the points open connect a 12V bulb between the moving point and a suitable ground on the engine. With the ignition turned on, the bulb will light up when the points open. With a wrench on the hex nut rotate the engine forward slowly until the F1-4 hash mark on the ATU is in exact alignment with the index pointer mark on the plate fitted at the rear of the stator plate. If the ignition is correct, the points should be on the verge of opening when this position is reached. This will be indicated by the flickering of the bulb".

It would seem to me that the far left l T top dead center hash mark would not be the correct mark to use based on the instructions above. Do these instructions describe what is being refered to as the "static set up" mentioned by GregT?

Thanks!

GS750GUY

 

[Suzuki_Don]

Remove a spark plug in either cyl 1 or 4 and find true TDC and then see which of the timing marks on the ATU lines up with the stationary line on the back plate. This is then the TDC mark and you can eliminate this line from the equation. Be it the left or centre line. And work on from there.

 

[Guest]

Use the middle line.

 

[GregT]

Use the middle line when doing it the way you specify.
If you are running out of adjustment check your points gaps - I prefer to set them to the small end of the range specified in the manual.

Greg T

 

[GS750GUY]

Use the middle line when doing it the way you specify.
If you are running out of adjustment check your points gaps - I prefer to set them to the small end of the range specified in the manual.

Greg T

Thanks GregT!

The middle line makes sense to me now when thinking about the process of ignition. If my thinking is correct, the middle line marks the point when the points are just beginning to open in order to create the spark and finally when the engine rotates a little further the gap opens far enough to create the spark about the time the piston reaches top dead center in order to fire the cylinder.

I'm also just curious about your statement about prefering to set your point gaps at the small end of the range. Do you have mechanical reasoning for doing this? I was wondering about this very issue when reading my service manual and wondering what measurement I should use to gap the points.

Thanks for your help! Always anxious to learn more!

GS750GUY