A: There is no “pre-determined” combination of rods and jets for any given motor, accept for altitude corrective applications, which is 4% for every 3,000 ft of elevation. Every engine is going to require a different fuel curve. The best thing to do is run the carburetor on the engine right out of the box to build a baseline, then check the spark plugs and see how they look. You need to have a light brown, or tan color on the plugs. If they are too white or too black, you need to make adjustments, refer to the tuning chart in your carburetor owner’s manual , Plug reading gives you an accurate idea of what is actually taking place inside the combustion chamber. Please note, today’s re-formulated fuels can leave a lack of accurate colorization. To order replacement parts via mail, To purchase replacement parts online,