Here are a few things I dug up. Is your meter like this?
http://www.sears.com/search=dwell%20meter?catalogId=12605&storeId=10153&levels=Tools&autoRedirect=true&viewItems=50&redirectType=CAT_REC_PREDI knew you guys were correct, but I couldn't figure out why... Then it hit me.
A typical V-8 car's distributor sends a total of 8 sparks per distributor revolution (it turns at cam speed or 1/2 engine speed). The points cam lobe pitch would be 45 degrees (360/8=45). So what the dwell meter is actually measuring is "time points are closed per 45 degrees of distributor rotation". A V8 dwell meter is set up to display units of " degrees of points being closed (or is it open?) per 360 degrees of distributor rotation". Therefore, In order for the meter to display the correct units, the scale of the display must divide the actual measured dwell by 8. On a CB750, the points are attached to the crank, and therefore rotate at engine speed. CB750 points only fire once per rotation.
IF the target points duration is 195 degrees for a cb750, that is 195/ distributor rotation. In order to convert to what the V8 dwell meter would read, you simply have to divide 195 by 8.
195/8 = 24.3.
From TT
Dwell is the duration of crank rotation that the points are closed in degrees. If you set the point gap correctly, you get the proper degrees as it is machined into the points cam. Honda says that this is 195 degrees. Few dwell meters are calibrated to display this number for the SOHC4 and its wasted spark ignition cycle. Dwell meters will have to be calibrated/ or interpreted for the number that it does display.
My calibration technique is to set brand new points to the gap specified, attach the dwell meter and note the indication. Thereafter, you can use the noted reading to adjust used points for the same reading.
Cheers,
N, The dwell meter is simply a "more accurate", way of adjusting your' points gap.. as it indicates the # of degrees of points cam duration points are closed. Points wear in two directions, 1st at the "rubbing block" and 2nd at the "contact faces" both alter the amount of "saturation time" the coils see to provide optimum spark. handy to know, (perhaps) but of little import in the "real world" a set of feeler guages or a buisness card in a pinch do fine for setting gaps. more important (as long as gaps are close) is where spark occurs. thus the need of a "timing light" and the "slotted " breaker plate. on "older" english twins, you "set" the timing on 1 set of points, then opened the gap on the 2nd set to make "timing" match... dwell & gap be damned.. Honda & other period 4's mount the 2nd set of points on a "movable" plate allowing timing on 2nd set of ponts to be changed while retaining "same " points gap, hope this helps luck G
Are you using an automotive dwell meter (like most folks have), or one that is motorcycle specific?
medic09
If you have a Clymer, it tells you "Make sure the meter is calibrated for small gasoline engines of 2 cylinders (one point set controls 2 cylinders). On a 4-cylinder scale, the correct dwell would be 46-49; and on an 8-cylinder scale, 23-24.5."
Steve F
When I use my dwell meter, I use the 8-cyl. scale and the reading should be 23 to 24.5 degrees, this is based on the Clymer manual which says 2-cyl scale=92-98 deg., or 46-49 deg. on the 4-cyl. scale. Since my meter apparently only reads the 8-cyl. scale correctly, I go with the 23-24.5 deg.
Hook-up is simple, black lead goes to the ground, and the red lead goes to the same connection as the condensor.
Adjust the point gap until you get the correct reading, lock 'em down and then set your timing.
This could go on and on.
