76 GT250 ignition timing

[craigm]

I have a problem with the timing on my 1976 GT250. I have set the points gap to 0.014' as per the specs but cant seem to get the them to open at 2.05mm before TDC- lining up with the timing marks on the stator plate. I have moved the plates on both to full retardation and I'm still not on the marks?
haven't checked this with a dial indicator yet, but do these have a habit of not being on the marks?
maybe the pictures can show what I mean

 

[crazypj]

I did a ton of them when I worked at Suzuki dealers.
Always used dial gauge down plug hole
Did you set points gap at maximum opening or did you set it at the timing mark? (max opening pposition is about 90degrees past timing mark)
If it's totally impossible to get timing right and you set points gap at max opening, the 'heel' of points is probably worn, the felts look pretty dry so that is a possibility?
You could always try 0.012" or 0.016" as anywhere in that range will be OK

 

[craigm]

Yep I will have to use a Dial indicator to check the degree/ mm before TDC.
I set the points gap on the back of the cam at maximum opening, and they are new points although this build has been on and off for a few years
I found a service bulletin about the stator being re-stamped due to the timing change for the 76 model, but it only gives a frame number range that this would have applied to, and I don't think that my engine is the one for my frame originally? but could this be something?
Was it common for them to be outside of the marks?

 

[crazypj]

Pretty common.
You should really remove the rotor and check the Woodruff key on crank, it could be offset or sheared (that was real common if taper wasn't perfect.)
Use fine valve grinding paste to lap rotor to crank (almost forgot about that as I haven't had to do it since about 1980~81)

 

[craigm]

I have done some more with this and have found that when I checked the timing with a Dial indicator, it was inline with the marks on the rotor @2.08mm BTDC. my points didn't open until 1.2mm BTDC , and this was also at full advance on the points plate .
What I did notice was that the rotor has T250 stamped on it - do they all have this? I am also wondering if the points cam is different between the models as I was thinking about removing the locating pin and re-indexing it to open my points at the correct time.
Any advice welcome.

 

[crazypj]

As far as I remember, the rotor is common to the twins from 1967 (maybe even older?)
If the points gap is correct at max opening, you can open or close it a few thou to get timing right.
Slightly smaller gap (0.002") will improve spark but you may possibly get a missfire at higher rpm as points can bounce easier

 

[Hurco550]

I'll check my guide when I get home, but the btdc did change from what is was in 75 for the 76 to 77 rotors. Check out the Oz books for the service bulletins as well. I just finished up my 76,and 76-77 had a bunch of stupid 2 year only stuff on em. If I remember right, the early 76 had the wrong timing marks on the rotor from the factory. Here in a bit I'll try to find some of the data I found

 

[Hurco550]

Here ya go.

http://www.ozebook.com/compendium/techbuls/

 

[Hurco550]

I have done some more with this and have found that when I checked the timing with a Dial indicator, it was inline with the marks on the rotor @2.08mm BTDC. my points didn't open until 1.2mm BTDC , and this was also at full advance on the points plate .
What I did notice was that the rotor has T250 stamped on it - do they all have this? I am also wondering if the points cam is different between the models as I was thinking about removing the locating pin and re-indexing it to open my points at the correct time.
Any advice welcome.

Sorry man, I somehow missed your post that you already found this info. Sorry I couldn't be of more help man

 

[craigm]

I ended up modifying the points cam to get the required advance by removing about half of the locating pin.would be hard to put back to original if needed.
RH side is still right on the edge of its adjustment on the points plate, but LH is in about the middle of its adjustment.