Ignition Timing - Honda 180-Degree Twins First thing to do is make a quick test light - I used a 12 volt indicator bulb from a speedo. Test leads with alligator clips make hookup easy...
The point plate and assembly looks like this - Behind it, attached to the camshaft and spinning rapidly, is the spark advancer unit. The one pictured is pretty well funkified, needs a good cleaning...
This is old-school stuff, a purely mechanical device. As you can see, the foot of the point rides on the outer sleeve (which is eccentric) of the advancer sleeve - this levers the point open and closed. As the advancer spins faster and faster, centrifugal force causes the little weight things to pivot out against the pressure of the springs. As they do, their other ends cause the outer sleeve (with the lobes) to rotate, advancing the timing. At about 3,700-4,000 rpm or so the timing should be fully advanced. The whole advancer can be disassembled pretty easily for cleaning - the sleeve just sort of wiggles off - it is possible to put it back together 180 degrees out of whack, so you have to pay attention to that.
The Procedure (Static Timing) Remove the spark plugs. Remove the round alternator cover, and use a 14mm wrench to turn the crank counter-clockwise, as viewed from the left side. Rotate until each point is at its widest opening, then use a feeler gauge to set the point gap on both sides to about 0.014", or so. Hook up your test light as shown below, and turn the ignition key ON. (The other lead of the test light is connected to a ground, off camera.)
Put your finger into the Left spark plug hole, plugging it. As you turn the engine over with your wrench, you ll feel/hear the air being compressed in the cylinder as it approaches the top of compression stroke. You want to align the LF mark on the rotor with the index mark on the coil/stator.
The Left point should open and the little light should come on EXACTLY when the LF mark aligns with the index mark. Loosen and turn the entire point plate to do this LEFT side ONLY, do NOT change the point gap. Yes, it is normal for the engine to try to run by the mark as you approach the top of the stroke. And it s not considered good to turn the engine backwards (clockwise, viewed from the left). So this is something that takes a little practice, and patience. Things may move a little bit while tightening - check and double-check everything. When you re convinced the left side is ok, move on to the right side. Move the clip on your little test lamp to the right side point. If you turn the engine exactly 180 degrees from where you were for the left side, you find another pair of marks on the alternator, F and T. Now we want the right side point to open EXACTLY when the F mark lines up with the indicator. However for the RIGHT side points, we do that by ADJUSTING THE GAP. Change the point gap to wherever it needs to go so that the light comes on exactly at the F mark. The point gap will still hopefully be somewhere in the acceptable range - but do not set it with a feeler after this point, it will change the right side timing.
If the right side gap ends up being outside spec (0.3-0.4 mm), then adjust the left gap to max or min spec, re-time the left by turning the plate - then re-time the right by changing the gap, and check to see if it s somewhere within specs. You may have to do it several times. If it just doesn t seem to happen, replace the points. I ve found that with new points, 0.014" on the left gives me a final gap on the right of about the same, and the point plate is nicely centered. Strobe Timing You obviously need a strobe for this - as you observe the timing marks on the rotor (engine running), you ll notice the timing advance to somewhere between the two advance marks on the rotor - this as about 3,500-4,000 rpm is hit.
Yes, there will be oil spray and some leakage. Put a piece of Saran Wrap over the business end of your strobe. Depending upon your application, you may want to favor one side of the marks or the other. For instance, racers don t even care if their bike idles, they re always at max rpm. If you static time your Twin, but notice the strobe isn t showing proper advance, then the advancer is goofy. Now, lots of stuff can go wrong with advancer units. They can get dirty and stick - they can stick open, closed, in-between, or just be sticky... And this usually happens when it s been running and is very hot, too hot to mess with it, or even check it. The springs can get worn out - that would cause the advancer to kick in too soon, at a lower rpm. Some folks shorten the springs slightly, but there s the danger of too much tension on the springs, which means the advancer would kick in too late, at a higher rpm, and might not advance fully at all. I ve seen folks manipulate the little tabs in this photo - usually they add a bit of shim inside it so the tab physically stops the advancer weights at a particular point.
On a practical level, I m more concerned with ultra-snappy throttle response, and on a 450 that comes from a simple static timing routine. I check the advance with a strobe once in a great while on 450's, just to see if it s actually working. 350's on the other hand, respond best to a strobe tune, so...be advised. Notes: Many times aftermarket point plates look good, but have the wrong screws holding the points down - the arrows indicate the screws in question. If the screw heads are too large, they will physically prevent the points from opening more than about tenthousandths inch. The stupid little problem can cause a lot of trouble if you don t catch on... Also, 450's are notorious for shorting out the right side point when you put the point cover back on. If you seem to have right side problems, try running with the point cover off and see if it clears up. A couple of extra gaskets there may give you enough clearance - or try manipulating the spade connector on the point wire a little.