Have left all idle screws at 3.5 turns out and don't have a colour-tune plug to fine tune - is there an alternative?
There is a technique used in the auto industry to set up the idle mixture screws to " Lean Best Mixture" On a car with either a 2 barrel or a 4 barrel carburetor, the carburetor would be mounted to a typically dual plane manifold, meaning each of the primary barrels would be feeding 1/2 of the engine. So similar to what we have with the KZ1300 where 3 carburetors are feeding 6 intake runners, so bearing that in mind -
Start by setting all of the idle air mixture screws to 3.5 turns out
Warm up the engine to operating temperature.
Adjust the idle to 800 - 900 rpm.
Open up the air mixture screws 1/4 turn and watch the idle rpm. If it climbs it means the air screws are still too lean, so open up all the screws another 1/4 turn. Keep doing this until the idle stops climbing. Chances are, 3.5 turns out is already too rich.
Now you're going to turn in all of the idle air mixture screws 1/4 turn and watch the idle looking for a drop in rpm. If the idle doesn't drop, it means the mixture is still on the rich side so turn in the air mixture screws another 1/4 turn and watch for the drop in idle. When you reach the point where the idle drops, that's "Lean Best Mixture" and if you were using the Gunson Colortune, that would be where you found that rich blue flame you're trying for.
Now that you've found Lean Best Mixture, you want to crack the throttle from idle and listen and see if you have a "just off idle bog" , meaning as you crack the throttle the rpm's drop then rev up. If this happens it means your too lean on the idle circuit and you're too lean for a nice transition to the Main Circuit, so you want to open up the idle air screws a 1/4 turn and repeat, looking for the happy spot where you can crack the throttle and no bog.
This probably as good as it gets without using a Gunson Colortune and I say this because depending on how clumsy previous tuners have been when closing the air mixture screws down to closed before opening them up, it is possible to make the orifice in the carb body larger with the taper on the air mixture screw if you're too aggressive when tightening down on the air screw and that will affect how each air mixture screw works compared to the other air mixture screws. With the Gunson, it's easier to find that perfect blue flame on each cylinder.
Hope this helps,
KB
Topic Author
