High-speed Needle Tuning
Start the engine and run your vehicle around to get the engine up to operating temperature. Now you can start the tuning process with the high-speed needle. The changes made to this needle will affect the low-speed needle and idle settings, so the high-speed needle is adjusted first. You’re looking for an engine temp range of 220–230°F, and you’re going to use the high-speed needle to get it there. After running your vehicle around for about two minutes, bring it over and check the engine’s temp as quickly as you can because the longer it sits, the cooler it will get. If the temp comes in below 220°F, it’s running too rich and you’ll have to turn the needle clockwise to lean the air/fuel mixture. If your engine is running above 230°F, your engine is too lean and you’ll have to turn the needle counterclockwise to richen the air/fuel mixture. The further away from the temperature goal, the more you have to adjust the needle. Bring your vehicle over; check the temp of the engine; and after making the appropriate adjustment, go back to running it; after another two minutes, check the engine temp again. Repeat until you get the temperature in that 220–230°F range. This is a general temperature range that you’re looking for when tuning, but you may find that the setting when the engine is at 230°F is still too rich and you’ll need to lean the high-speed needle out a little bit more and maybe run at a temperature of 240°F. When your engine is running properly, it will produce good power and have a trail of smoke. If the engine is too lean, it will run well for the first couple of feet, then power will be reduced or the engine will shut down altogether. An engine that is too rich won’t have much power at all and there will be excess fuel spitting out of the exhaust. Starting off a little cooler than you want isn’t a bad thing because, as you run the engine, its temp will rise slightly.