Final carb adjustments help needed

I've got a 1976 kz900 with stock carbs, pod filters, 4into1 Kerker pipe. 17.5 pilot jets, 120 main jets, needle is clipped on the middle position. The bike has a flat spot in the throttle response in low rpms and a plug chop showed all plugs exactly the same amount of slightly to lean. Air mixture screws are 1 1/4 turn out. These are the carb with the mixture screws on the side. I'm wondering which way I should go from here. Any help is appreciated.

Your jetting is about spot on. I would check your mechanical advance under the points. Make sure it is operating freely and not frozen up.

agree check advance and timing.Also air mixture screws should be adjusted individually.Raise rpm's 3000 , start at 1/2 turn out slowly turn until slight bogging or rpm goes up , find the sweet spot.Each cylinder may breath a little different.Emgos?

I should have mentioned that I installed the Dyna 2000 electronic ignition and no longer have a mechanical advance and according to the led on the Dyna unit timing and advance are set perfect. I'm not sure what you mean by raising the rpm to 3k and then turning the mixture screws. The bike idles perfect at 1200 rpms. The problem is it bogs at low rpms and was tuning to lean.

Does anybody know what the distance from the bottom of the carb body to the bottom of the floats should be?

Get rid of the cheap filters if that's what you have. I couldn't believe the difference when I switched to Unifilters.

Have you checked voltage to the coils? Can you describe low RPM's in a little more detail? Suggest taping your switch block and marking throttle positions to get an idea what circuit you're dealing with. Take it for a ride after warming up and find the flat spot start and end in 1st gear with respect to throttle position.

Haven't tried tuning the air screws at 3k rpm, seems a bit high, like maybe you would have a lot more influence from the jet needle and needle jet. But maybe it works?

Alan

SeattleKZ wrote: I'm not sure what you mean by raising the rpm to 3k and then turning the mixture screws.

They mean crank your idle stop screw until the bike's tach reads about 3k. Then start to fine tune and adjust your air mix screws.

You want to listen to the engine and turn each screw 1/4-1/2 turn at a time. Listen for the engine idle to change. You'll hear it but likely won't see it on the tach.

My understanding from my manual is that you want to set each screw at the point where you get the highest idle.

The Sudco Mikuni tuning manual says to raise the rpm 10-20% above the target idle, like 1100-1200 rpm. 3000 rpm would be 200% above the target idle. I'm not saying it doesn't work, because I haven't tried it. But I can say 1200 rpm does work for audibly tuning the screws, given everything else is in working order.

Alan

Thanks everybody for chiming in here. I changed the pilot jets from 17.5 to 20 and that seemed to solve almost everything. Tomorrow I'm gong to adjust the mixture screws to get it dialed the rest of the way. I always thought those mixture screws did something else. Now I understand what they're are doing. I went for a ride and checked the plugs and thet are perfect.

After talking with some people who focussed just on my carbs about the issues I had I followed their suggestions.

I have a Kerker 4into1 with pods from Z1. I live in Seattle so basically at sea level or 1000 feet above.

I am running 20 pilot jets and 120 mains with the needles raised all the way up on the clips. I adjusted the idle screws with the bike running at around 1500 rpms and was able to get it set to perfection. The bike has perfect throttle response through the whole rpm range and the plugs look like a perfect mix between rich and lean. So Now I'm off to go riding.