Topic: '75 CB750K5 runs rough

[woddy22]

I'm going crazy and need some help. I've got a '75 CB750K5 that I just can't get right. I've had the carbs off 3 times trying to figure it out. New points, set timing perfect at about 900 rpm's. Don't know about the higher rpm timing though, when I try to set it it seems like the advancer bounces around a lot and it's hard to get a good fix on the timing marks..bike fires up like a champ, idles good but when I get it out on the road it breaks up a lot....I think on a seperate issue sometimes when it's just sitting and idling the rpm's start to climb and it starts racing  but a quick turn of the throttle and it set back down. That's probably an air leak someplace?? But I think the breaking up when I'm on the road driving is caused by timing adjustments... I changed out the timing advancer ( I tried another used one) but I get the same results....any secrets to timing these old Honda's???

Thanks all

[Johnie]

Trying to read all your symptoms here...sounds like under load is when you are noticing a lot of the problems.  Did you remove the carbs, clean and rebuild them or why did you take them off?  Did you check the float levels?  Did you bench sync those carbs before you put them back on?  Did you sync them at all?  Did you adjust the valves?  To check for an air leak at the intake rubbers spray some WD40 on there while it is running.  She will speed up if you have a air leak at that point.  When you break up at the higher speeds that could also be a carb issue (floats, etc.).  Just trying to give you some avenues to cross here.  Let us know how you come out.