Topic: cb750 valve timing

[FondaHonda]

OK, I don't know much, I'll admit. My 1972 cb750 is hard to start when it is cold. I cleaned the carbs, replaced plugs, replaced battery. I tried checking valve clearance. I probably should have left it alone, it's even harder to start now. It apparently has aftermarket points (they are incased in rubber where the points should be). I have to turn it as far clockwise as I can to get it to start and idle (roughly), any adjustment the other way makes it stall. I know when I worked on cars that the distributor could be "off a notch" so you would have to pull the distributor and turn it a notch to get it right. Is this possible on this bike? If things are off, how do I know things were really at tdc when I checked the valve clearance? I'm getting discouraged and could use some help. This is the time of year when I should work on it so I appreciate your advice.

[MRieck]

Turning the timing plate clockwise retards the ignition which explains why it will start cold in that position. You had better go back and check your valve adjustments using a manual. It is easy to screw it up. It sounds like you are not achieving adequate compression to light the engine when cold. Figure out what type of electronic ignition is in there too.

[HondaMan]

Also, check the spark advancer. Are the springs and weights free? Does the advancer advance when you turn it by hand?

And, like MR said, what kind of ignition is it? Dyna? Martek? Other?