Skipping sparks, not running smooth on stationair

[CR9000]

Hi all! I am still rebuilding my CB750 ‘79 kz DOHC. DNA air pods with 4 in 1 exhaust with open muffler. He runs ok and starts emmediatly (with a bit of choke). But when running I can hear he is skipping some strokes. Now I did the timing with a timing light on the cable of spark plug cyl1. ( the timing was nicely in spec of the 2 marks, and 0,4mm between points)I noticed the light skipping strokes as well, and this were the same strokes I heart it skipping..

So am I looking at a faulty bobine which is skipping sparks? Or can this still be carb sync (in my opinion the spark would still go, dispite unsynced carbs). Anyone experience with this? Thanks in advance guys [emoji1431]

 

[pidjones]

I have experienced this with a rough point cam. Is there any roughness, rust, hardened build-up on yours?

 

[CR9000]

Thanks for te quick respons!
Well got an electrical ignition and the two points are pretty clean and set them on 0.4mm. On the 2 coils I have 2 Ohms, doesn’t that have to be 5? And between the spark holders I have 21.1k Ohms and on the other ones no reading with the caps on, 23.2k without them. But when I attach them, I do have spark.

 

[pidjones]

There should be a 5k Ohm resistor in each cap, - OR- a 5k Ohm plug - not both! The resistors in the caps some times fail, often just from corrosion of the resistors or contacts. If you run the resistor plugs (the fancy iridiums are most all resistor), make sure no resistors in the caps (you can replace them with a short piece of solid copper wire). And sometimes, it is just best to spring for new caps. They aren't that expensive.

 

[CR9000]

I’m guessing those are the originals, so I’ll check that in a couple of hours and maybe order some new ones without Resistor. I’m going to messure the secondary’s of the coil too, without the cables this time. Hope this gives me a reading. Otherwise I am ordering a new one. Best 2 Ohm, 3 or 5? Or doesn’t matter? I’ve read on here the 2’s can fry your spark units?

 

[pidjones]

Seems that I remember 2 or 3 ohm primaries and 12k ohm secondaries. Only go non-resistor if using resistor plugs. You need 5k at the end (plug OR cap) to reduce radio interference. I think only allowed no resistor on race bikes.

 

[CR9000]

Got 2,5 ohms on primary an 12.6k and 14k on secondary without cables/caps. So I am ordering caps without risistors and new cables. I did have reading of 5k ohms on the caps indeed!