Ignition Quirks…”Split-Timing” Technique

For the static timing light needed for this procedure Click here

Robert Overby wrote a very interesting article titled “Improving Your GL1000’s Performance” which appeared in Wing World in the June 1995 issue. You can find this article by searching the GWRRA Message Board Archives (see my links page). This is a GREAT article that explains some weird design problems unique to the GL1000 ignition system as well as methods to resolve them. I guess I’m a bit of a contrarian, but I like breaker point ignition systems. In my opinion, no one needs to resort to an electronic ignition system to have a decently tuned GL1000.

If you blithely set the breaker point gap and static timing “by the book” without consideration of Robert’s revelation, you will most likely introduce 2 unintended (bad) consequences. I give full credit to Robert for solving these mysteries.

I’ll try not to go into a deep technical explanation (read Robert’s article!), but I will summarize what you need to do to get great results. First, you need to understand that the GL1000 relies on a “wasted spark” system in which each coil fires 2 plugs simultaneously…one on the compression stroke (working spark) and one on the exhaust stroke (wasted spark). This is why you have only 2 breaker cam lobes firing 4 spark plugs. There’s nothing wrong with this system in theory or practice. Many other motorcycles use this design without a problem. The engineering advantage is that it reduces the number of parts required, eliminates potential points of failure, and saves weight (you only need 2 coils instead of 4).

The breaker cam / advance mechanism is mounted onto the end of the left camshaft. Here’s the first unexpected problem – the left camshaft is adequately supported by its bearing surfaces in the left head to do its main job of opening and closing the valves. However, the bearing support does not prevent the aft end of the cam (where the breaker points are) from “walking” around in a slight wobble. This effect is caused by camshaft flex induced by valve spring pressure. This anomaly is just enough to disturb ignition timing. The good news is that it (usually) only affects the timing of cylinder #1 and #2.

Wear or “slop” in the eccentric that operates the points can make the problem worse. Ditto for problems with the ignition advancer.

Here’s how to judge: 5 degrees of timing equals about 7/16″ inch on the flywheel …5 degrees is also the distance between the “F” and “T” marks (this is the value on ’75-77 models.  Later ’78-’79 models have 10 degrees between the “F” and “T” marks).

Move the base plate so that you “split the difference”…one cylinder will be a little early and one will be a little late. You don’t really need to keep track of which cylinder is early or late, just make certain that the “early” cylinder never fires more than 2 degrees before the F mark. If you just go “by the book” and don’t follow the procedure described above, you can end up with 1 cylinder up to 5 degrees earlier than the F mark. This causes the low speed to knock off the front of the engine many GL1000’s exhibit. It’s hard to recognize because it’s actually a “spark knock” of an engine under no load, but only affecting 1 out of 4 cylinders. “Splitting the difference” is not a perfect solution, but it gives you an acceptable compromise with much smoother idle manners.

When you’re done, set the timing for #3 and #4 relative to the F mark for “2” on the flywheel by moving the points sub-base (there shouldn’t be any appreciable difference induced by “wobble” on this set).

Here’s the second problem you can have, even when you carefully follow the workshop manual. The spec for the breaker point gap is listed as 0.012″ – 0.016.” Without coaching, most people will aim for the middle (0.014″) as a hedge against their less than expert skill with a feeler gauge. Again, I’ll skip the theory, but if your point gap is on the smaller end of this range you can end up with a problem called “dwell overlap.” Dwell is defined as the duration of time that the points are closed and the primary winding of the coil is energized.

Basically, you want to make sure that you never have both sets of points closed at the same time. If you do, the non-isolated nature of this design will allow a voltage drop that can dissipate the saturation of the second coil and cause a weak, unreliable spark.

Don’t worry about electrical engineering theory. Here’s what you do. Aim for the “high” end and set the breaker gap at 0.016″. Next set the timing per the special instructions above. Then using your test light, ohmmeter or buzz box rotate the engine through several revolutions (for each set of points). As detailed above, the points for #1 and #2 should OPEN at +/- the F mark for “1” on the flywheel. Now make an additional check to determine that they do not CLOSE until AFTER the F mark for “2.” If they close early, you need a more point gap which results in less dwell. Each increase of 0.001″ point gap reduces dwell by about 4 degrees. Note, each time you adjust the point gap, you MUST reset the timing!

Once you’re happy with #1 and #2, repeat the procedure with #3 and #4. In this case, the points for #3 and #4 should OPEN exactly at the F mark for “2” on the flywheel AND they should not CLOSE until AFTER the F mark for “1.

“ This all sounds complicated and I’ve described it in several steps and in more detail than I intended. In practice, it’s quite simple. Here’s all you need to do in a step-by-step summarized sequence:

1. Set the point gap for #1 and #2 at the max. end of the range (0.016″)

2. Set the timing for #1 and #2 using the “split the difference” method relative to the F mark for “1”…early cylinder no more than 2 degrees before F mark for “1”

3. Check that points for #1 and #2 CLOSE after the F mark for “2”…if not increase gap, re-time and repeat this test

4. Set the point gap for #3 and #4 at the max end of the range (0.016″)

5. Set the timing for #3 and #4 relative to the F mark for “2”

6. Check that points for #3 and #4 CLOSE after the F mark for “1”…if not increase gap, re-time and repeat this test

Once you get everything set correctly, minor maintenance is reduced to periodic cleaning and re-gapping of the points to the max. value. You don’t have to futz with timing every time.

Point of clarification which confuses some people: The “1” and “2” marks on the flywheel do not refer to cylinder 1 and cylinder 2. Rather the “1” on the flywheel [and it’s associated T (Top Dead Center), F (static ignition fire), and Full Advance marks] refer to all of these events for both cylinder 1 AND 2 and the associated set of ignition points for cylinders 1 and 2. The events are phased 360 degrees apart.

Likewise, the “2” on the flywheel [and it’s associated T (Top Dead Center), F (static ignition fire), and Full Advance marks] refer to all of these events for both cylinder 3 AND 4 and the associated set of ignition points for cylinders 3 and 4.

Odd observation. I’ve worked on a few bikes that had the timing variation on cylinder #3 and #4 instead of the expected timing variation on cylinder #1 and #2. I have no explanation for this. The cure was the same…split the difference in timing on #3 and #4 with the early cylinder no more the 2 degrees before the “F” mark.

Tip: Be aware that there are 2 ways to hook up your static test light. The light will go “on” or “off” at “F” depending on the method you use. Either method is fine. I use the light “on” at “F” (light comes on as points open). This requires that the ignition switch and kill switch are both set to on.

Another Tip: Contrary to some manuals, ignore the punch mark(s) on the eccentric breaker cam when setting points gap. They were not created very precisely by the factory and amount to an unnecessary distraction. Just aim for the highest point on the cam lobes and then set the points.

Yet Another Tip: To avoid the unnecessary distraction of a test lamp that alternates between bright, dim and off-put a small piece of paper (like a section of a business card) between the points on the side you are not adjusting. This will allow your test lamp to have only 2 modes: bright and off. Without this step, the activation of the “other” coil will make your test lamp dim in a distracting fashion.

Final Tip: The aftermarket Dyna/S electronic ignition conversion is triggered off the end of the left cam and retains the OEM spark advancer. Dyna/S equipped bikes typically exhibit the same “wobble” as bikes with breaker points.  The cure is the same: “split the difference.”

Key notes: 

• https://www.randakks.com/catalog/product/view/id/5599/s/dyna-s-ignition-ds1-3-gl1000/
• https://www.randakks.com/randakks-honda-gl1000-static-timing-light.html

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