High Speed Carb Tuning.

[Old2stroke]

If you want to test if it’s dependant, close the H screw fully while the machine is idling, then gently open the throttle a bit (not fully) and it will bog or die. It may even die at idle just closing the H. If it’s an independent carb, it won’t be affected. It’s not something many know. Don’t be mistaken either they are most often genuine walbro carbs on those machines. That doesn’t make them a good concept, but it does make them decently made.

Not a brilliant design when the 2 screws are interactive and I can't think of any advantage it gives. I think Zama has done this too. I have modified a few of these carbs (mini macs) by plugging the low speed feed from the high speed circuit and drilling a new hole in the fuel chamber to give direct feed to the L screw. Easier to tune, less fussy and a side advantage is, due to the complete separation of the two circuits, it doesn't seem to have any problem with air bleeding back into the low speed circuit if the high speed nozzle check valve is left out.

 

[MoreCowbell]

Old2stroke,

With your mechanical ingenuity, you remind me of me - a machinist. (smile) I admire your cleverness and moxie.
I will continue tinkering with my Walbro and hope to get it (the H circuit) optimized.