Timing questions

Lance Weersma

XS650 Enthusiast
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Good day gents.
Last year I got my 72' running for the first time in 30 years. It has 25k on the motor and the PO and only owner is my dad. I put about 1000 miles on it but always had a back fire when I decelerated. I hopes of solving the problem I cleaned my carbs a out 10 times, New filters, plugs wires, battery, exhaust, ex gaskets... ect.

I am looking over my time this winter and had a few questions
I have gone through the standard cam chain adjustment, valve adjustment, gapped points and did a static timing adjustment. However when I use a timing light I can't get both the left and right to fire at the appropriate time. Either I can get the left to fire at the "F" Mark and the right is too advanced or I can get the right to fire at the "F" mark and the left is too retarded. I am adjusting them both independently but there adjustment does not give me enough to get me into the right location.

Any ideas?

Thanks in advanced
 
Setting these dual points can be a chore. Not only do you have to match the timing between the cylinders but you should also try to match the points gaps. It sounds like yours aren't. The right side may be too large and the left too small or the left may just be too small. Changing the points gap changes the timing. That's why you gap the points first before setting the timing. A smaller gap fires later or more retarded, a larger gap sooner or more advanced.

If your points are used, it could just be a worn out set. Sometimes they won't set properly. Also, worn points develop pits on their firing surfaces. The spark fires or jumps between those pits. You can't accurately measure the gap between pits with a feeler gauge. A dwell meter is the only accurate way to set used points. If you're using a feeler gauge, stay near or at the minimum of the gap spec.
 
Thanks. Will most multimeters do the trick or will I have to get a dwell specific one? I see a few older ones with needle gauges and then digital. Any suggestions?
 
Most multimeters do not have the dwell function. Usually, you need an automotive type unit. Besides the normal meter functions (volts, ohms), many of these will have the dwell function and sometimes a tach function as well. Here's a reasonably priced digital unit .....

http://www.ebay.com/itm/161823459197?_trksid=p2060778.m1438.l2649&ssPageName=STRK:MEBIDX:IT

I prefer the digital units. The number range you'll be reading is rather low and a needle type meter usually doesn't read that low very easily.

I've never seen a meter with a 2 cylinder setting. Most only have 4, 6, and 8 cylinder settings. But that's OK, you can use the 4 cylinder setting by doing a little math. For a 2 cylinder engine with a single set of points, you would divide the actual dwell value by 2 to read it on the 4 cylinder scale. But, since we have a dual points set-up here, you must divide the actual value by 4. The 650 dwell value is 93°± 5°, or 88° to 98°. Divide that by 4 and you will be looking to see 22° to 24.5° on the 4 cylinder scale.

The reading on a dwell meter is inversely related to the actual points gap. That means a smaller reading indicates a larger gap, larger reading a smaller gap. This is because the meter isn't actually measuring the gap or amount of time the points are open, it is measuring the time they are closed, or "dwelling" in the closed position. Since points usually gradually wear closed I like to set the gap as big as possible but still in spec. That means as near to the 22° reading as I can get.
 
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