'74 GT550 possible issue with points

[vdavidoff]

Hey All,

I'm at the point where I'm trying to start the '74 GT550 project I picked up. It looks like I'm not getting spark. This is my first dive into an electrical system (even one this simple) so I am looking for a bit of confirmation on what I think I found.

I am testing for spark by touching the spark plugs to the head while using the electric starter to turn the motor. I am not getting spark on any cylinder. I set the gap on the points to both .012 and .015 using a feeler gauge and cleaned them using contact cleaner and a business card and saw no change at either gap.

On thing I did notice, accidentally while trying to play with my multimeter, is that if i connect the points using one of the multimeter probes (actually, connecting the parts the points mount to, not the actual points themselves) then pull the probe away, I do get spark. This works on all cylinders. This makes me think my points are wasted or need a more thorough cleaning of some kind. Does that sound right? Is the test I did valid?

Thanks.
Andy

[Cliff]

You're on the right track Andy. Sounds like the contacts are dirty or corroded. Try giving them a light sanding with VERY fine sandpaper or crocus cloth. Make sure the contacts are clean and DRY!! Good luck with your project!

[vdavidoff]

Cool, thanks. I cleaned up the points with some fine (#000) synthetic steel wool and things are looking better. It's too late at night to be trying to fire the thing up (neighbors), but resistance looks good on all 3 points now and turning the motor with the kicker I get spark on the middle and right cylinders.

The left cylinder isn't getting spark, but I am now getting a spark across the points each time they separate, which based on another forum post seems to suggest that condenser might be bad.

I guess I'll mess with timing and try to fire it up again tomorrow, just to see if I'm getting closer. I think I'm going to go ahead and replace the points and condensers since it seems it's inexpensive to do so, but we'll see how things go tomorrow.

Thanks again.
Andy

[vdavidoff]

This morning spark was crappy again. Feeling that I didn't have much to lose, I totally pulled apart the points and gave them a better scrubbing (though I was still careful) with the synthetic steel wool. Put it all back together and the bike started for the first time in I don't know how long (when I bought it, it wasn't running). It sounds pretty rough but all things considered, better than I expected. Anyway, wooo! Now I guess I get to fine tune the fuel and spark situations. And see if in the mean time the points die.

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Andy

[vdavidoff]

Hrm, well.

I went to check the timing using an analog ohmmeter and quickly realized something is still very wrong. I'm surprised the bike runs at all.

One set of points seems to have totally failed again.

The other two, here's what's happening, and what I'm most interested in: Off the points plate, but still with all leads connected, their resistance reads properly open and closed. On the points plate, the resistance only rises to about 1 ohm when they're open. So, it seems as though they're shoring on the points plate, but my little mind can't understand how.

I held the points of one set open with a business card and confirmed I got inf ohms testing off the points plate. As soon as the point set touches the plate ohms run down to ~1. I realize there are all sorts of insulators built into the points - I saw them all when I took them apart to clean them. They look fine to me, including the little one that slides over the lead mounting bolt, but what baffles me the most, is that if those insulators /were/ the problem they should be a problem even when the points are off the plate, shouldn't they? But if it's not them, then what?

-- Update: I think I just realized I was being stupid about how I had the multimeter hooked up. Going to think more about it tomorrow.

Since one set is totally shot, I'm going to order new points all around, but I'd really like to understand what's going on, even if new points fixes it. Any thoughts on this?

Thanks.
Andy