Topic: CB750K1 Dwell- set at 27deg., is this too much or too little point gap?

[Yamahawk]

I am just messing with my dwell, and found it reads 27.1 on DMM and 27 on Actron dwell meter, what is acceptable dwell for my 1971 CB750K1? I set the points gap, and this is what I came out with. Now, I have read the posts on what the dwell should be, at 24 deg dwell, but would I just loosen the points screws on each side, respectively, and open or close the gap to lower the dwell reading to 24 deg... or, am I ok with 27 deg dwell? I haven't put a timing light on it either, just static timing so far. I have an old timing light from a flea market purchased years ago, which has the springy thing that goes between the spark plug and plug wire lol... might be time to order a new one from eBay.
Charlie

[TwoTired]

Understand that the true dwell period (points closed) is actually 190 degrees of crank rotation as determined by the points cam profile and the point gap setting.  So, whatever the dwell meter reports is an interpretation of actual.

Dwell meters are fine and all that.  But, what you need to do is meticulously set the mechanical gap with brand new un-pitted points, put on the dwell meter and mark what it reads.  Now you can use this marked setting to set your point gap instead of feeler blades or wires.

Cheers,

[Deltarider]

Honda specs says gap is acceptable between 23-24,5^o (on a 8 cyl scale that is). Gap at 27^o would be a bit too small if the bike was mine. Your motor may run fine with it, but for how long? Realise that pointsgap tends to decrease over time, so an initial 23 to 24^o is safer. If your timing light happens to be the old neon type, you may as well look for a bin; they're next to useless. Use a good xenon timing light instead, to check timing at full advance. Also check the functioning of the advancer and make sure its cam has some ceramic grease or similar on it.

[Don R]

 I got a new timing light with the springy thing one year for Christmas. It was shorted to the case giving me a good jolt, I took it back to Sears in April when I used it the first time. The counter guy thought I wanted the money,  He said we'll see about this and took it to the back. He wouldn't let me watch but I would have enjoyed it a lot. He looked shocked when he returned, he then offered a refund but I traded it in on an inductive pickup light.
 Long story short, bzzzzttt, I always preferred the inductive ones since then.

[Yamahawk]

Hehehe... yep would have LOVED to see the one too, Don... Deltarider, My light is Xenon, but its pretty old lol...  I am going to pick up an inductive type when I can.
I re-set the dwell to right about 24.7deg. on both points, they are good, un-pitted points, the gap opened up and stopped the intermittent spark that they were producing at the 27deg dwell, and it runs like a champ! Eventually, I will replace the points with a good set, and the condensers too. But for now, it's running well! It has straight through side pipes and crackles a bit on runoff, but hey it's got no baffles. I figure when I get the fishtail ends on it, that will give it less of a bark.
And, thanks for the tip, Lloyd! I set the gap pretty tight, at the lower end of gap setting, so that's why it was at 27deg dwell. I was surprised at how much more gap it took, to reach 24.7deg dwell! But now to is running pretty good. Thanks everyone for the input, and good advice!
Charlie

[TwoTired]

Point wear is a race between the contacts surface erosion and the rubbing block wearing down.  The former increases gap and the later reduces gap.

For the tec points the contacts wore well but the rubbing block didn't.  I always found the gap to shrink over time.  So, I tend to pick a wider gap at tune up time.

Cheers,