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Ignition-timing problem /Worn down points-"tabs"

Posted: Wed Jun 20, 2007 2:15 pm
by octane
The subject of being unable to get the
ignition timing right
as in: not being able to turn the points BASE-plate or sub-plate
sufficiently has come up a few times,
and have puzzled quite a few, yours truly included.

Both I and Whiskerfish has experienced that the problem lies in
the 'tabs' (rubbing blocks) being worn down to a certain degree
and the only solution is to replace the points.

Now I do think I've found the explanation:

New 'tabs' looks like this:


and worn down 'tabs' looks like this:


Let me see if I can explain what happens because of this

Imagine that this is a normal set up (shown with only the one set):
and the point of ignition (cam lifts the tab)
is where the line in the circle is:


now imagine that the 'tab' has worn down.
(On the pic below I have adjusted the points-gap AS IF the tap is worn down, but I haven't moved the BASE-plate)

When doing that; what happens is as you can see from the picture,
that as a result of twisting the points-plate,
the relation to the line (point of ignition) changes.
In other words: the ignition is now retarded.


In order to compensate for this and get the timing right again
you'll need to turn the BASE-plate.
The BASE-plate can only be turned within limits
(the oval holes in the plate)
and the above situation with the worn down 'tabs'
moves that point OUTSIDE the limits
and you just can not get the timing right.

I've checked and compared a pair of original
and a pair of after-market points, and I do think the
problem will set in earlier on the aftermarket points
as the shape and form is slightly different.

Mystery solved............I think .-)

The above also explains why you always need to
re-adjust the TIMING
after adjusting the POINTS gap.

Always check if your points-cam is rusted or pitted:


..if so: it will wear down the 'tabs' real fast.

help with a timing issue

Posted: Mon Apr 07, 2008 11:06 pm
by scmedic6
ok guys,

I have a few sorta stupid questions.

If you can help me get this thing fixed, I will ride where ever you are and take you out to lunch.

As I said in my intro, I have this 78 GL1000 that I am putting back on the road again. been down 4-5 years . I rebuilt the carbs but have a timing issue. ( reason bike was down so long was due to it being wrecked in 03.)

bike will not start, as far as I know it is not getting any fire.

Started timing it according to the instructions found on these pages.

1st question. when I set my timing mark to the F 2 mark as described, the cam lobe on the timing cam is pointed straight up. Is that normal?
if so it dont open either of the points right?
I took the timing covers off and checked the timing belts, look right.
What am I doing wrong?

Posted: Tue Apr 08, 2008 8:48 am
by Whiskerfish
Are you remembering that the Crank rotates 360 degrees twice for every single rotation of the Cam Shaft? One is the exhaust stroke and one is the Compression stroke. So the Lobe on the Cam will be 180 degrees out on every other rotaion of the Crank.

The Lobe on the end of the cam should just start opening the points when you line up the LH Points to F-1 or the RH points to F-2 respectively, again on every other rotation of the crank.

Posted: Tue Apr 08, 2008 9:22 am
by rcmatt007
fixed that one 29 years ago with a prestolite ignition.... however I still have the hardlyeverbeenused original cam and points plate

point setting 101

Posted: Tue Apr 08, 2008 9:15 pm
by scmedic6
Thanks for the starting place Whiskerfish. you are right. I rotated it 360 and the lobe wound up at the bottom.

next question Since it wound up at the bottom ,I have to rotate the points plate to the right to make them open up when the timing mark is on F2 right?

that means a lot of turning to the right. correct?

when I place the test lead on the blue terminal, it stays lit for a while and doesnt change when the points are open.

Posted: Wed Apr 09, 2008 5:12 am
by Whiskerfish
First you need to set the opening clearance of the points with your feeler gages. You do that by lining up the highest point of the lobe with the Point tabs so the points are open to their maximum. Set that for 16 thou clearance. Then you work on the timing, but remember to go back after the timing is set and verify your opening clearance. One does effect the other so it is kind of a balancing act. When working on timing you really only need to be concerned with the the beginning of the lobe, the place that the points just break contact with each other. The gap can be so small that you probably con not see it with your eye that is why we use a test light or meter.

You probably want to go to Randakks are do some reading on Tech Tip #7. It explains this process much better than I can. If you still have questions post them and I will do what I can.

Posted: Mon Apr 14, 2008 12:54 pm
by scmedic6
Whiskerfish, That info helped , got it fired up at least. Looks like Im heading to Norfolk for supper soon. Thanks for your help Ill E-mail befor I head your way. SCMEDIC6