836 kit carb and ignition tuneing

[bko62]

I have a 1974 cb750 with an 836 kit, stock cams, valves adjusted correctly. Dyna s ignition and two high out put coils and good wires.timing is set per the book. main jets have been drilled out to wire sizes larger then stock which is what the guy who do the cylinder bore told me to do.

My problem is that i get pinging ( pre ignition) in the mid range.Is there something i have to do like advance the timing? i have tried this and it didnt seem to help. I'm thinking of raising the needles. Will that do it? I know there are lots of these set ups running good out there and just what some direction . I really want to get this great looking bike runnin right this season .

Yhanks

[ynotabike]

pre ignition is too much timing...try retarding the timing. If you raise the needle's you will run more rich. Do a plug check. 3rd gear hold mid throttle for 15-30 seconds then pull in clutch and shut off engine at the same time. Check spark plugs. If black to Rich...If white to Lean. If Brown good!

[Re-run]

The dyna s does that. Did you time it at full advance? That is how it is supposed to be set up. Make sure it is timed that way. We have a set up manual for the dyna-s on this site.

Also, never drill a jet. Your best bet is to get new ones. Reason is that a jet is designed to be a venturi. When you drill it, you remove that effect and the jet does not work right.

Are you using the stock airbox and filter? What position are the needles currently in?

What exhaust do you currently have?

And last, what color are your plugs right now?