Topic: '77 CB750 Revival - Help!

[Radski]

Soooooo... I've picked up a '77 CB750 from a friend of mine and am going through the paces of getting it fired up and back on the road. Admittedly, I AM a newbie and at 40 years old after having a stroke, I'm trying to pull out a bucket list project to check off.

I'd like some help or suggestions as to what to do with one issue I've encountered thus far.

I've adjusted the valve clearances already and checked the tension on the timing chain. However, I'm encountering a weird electrical problem which is stumping myself as well as some slightly more experienced mentors. Im not getting spark on my 2 & 3 spark plugs however I do have spark on 1 & 4. I've checked all continuity and all wires from the points/condensers to the coil connectors and we're good. I've checked the continuity of the wires into the coils and we're good. I actually switched the coil wire connectors (yellow lead to blue coil wire, and blue lead to yellow coil wire) and then I got spark in spark plug number 2 but then didnt in 1& 4. I turned it over and looked at the points and have spark on the 1/4 point but did not see any in the 2/3 point. I checked the timing and its good and the gaps on the points are appropriate and clean flat heads.

What could be the problem? Why no spark? I'm fairly sure the points are worthy but....condensers? Point bad?

Any ideas or suggestions would be great!

[754]

 Clean 2 3 points., when you open them with a screwdriver does it  spark the plug.?

[Radski]

I did take some sand paper to clean off the points which were not bad at all. Pretty clean and gapped appropriately.

I did not try the screwdriver as you suggested.

[754]

May not want to do it inside, I had a backfire in a Carport once, about scared me off the stool I was sitting on..
 Loud like rifle..

[scottly]

The points have to "make", or contact each other, then "break", or open the connection; this is why they are sometimes called breaker points. The spark happens when the points open, breaking the connection from the points side of the coil to ground.

[02z06dave]

It would seem to me that if the problem followed the coil, then the coil is probably bad.

[PeWe]

Problems follow the point, right?
Shorted condenser? Switch them and see if the problem will change.
I had issues when starting my last CB750 k2 build for the first time. Ran on 2 only. I think it was 2-3 that did not fire. I wished that the problem was condsenser and not bad connection to coil under tank. I have extra condensers.

Replaced the condenser and all 4 fired up direct :-)  I could not see any problems how the previous one was connected to point.

[Radski]

Problems follow the point, right?
Shorted condenser? Switch them and see if the problem will change.
I had issues when starting my last CB750 k2 build for the first time. Ran on 2 only. I think it was 2-3 that did not fire. I wished that the problem was condsenser and not bad connection to coil under tank. I have extra condensers.

Replaced the condenser and all 4 fired up direct :-)  I could not see any problems how the previous one was connected to point.

Thank you for this suggestion. I wont be able to work on the bike until Monday/Tues next week. I've got a spare points setup that I know worked so perhaps I'll start with switching the condensers to see if that works...perhaps working up to replacing each part along the way if no success.

Thanks! I'll keep y'all posted.

[Don R]

Make sure the points close all the way, I had a bad set that could not be adjusted properly.