What needs to be done,...is pay attention to how this change effects your engine performance...
It usually requires some jetting changes...
Read my guide, and do these tests, and follow the recommendations...
Serowbot's carb tuning tips for beginners... Quote:A good indicator of overall jetting is the weather...if popping/backfiring increases on humid days, or at higher elevation, that indicates rich....less popping at those times indicates lean.
Drill out the brass plug on the idle mix screw... adjust for smooth and steady idle... if it needs more than 3 turns out, go one step larger on the pilot jet. The pilot jet will have an effect on MPG's... If you want good gas mileage, don't get carried away there...
CW, in, is going leaner,... CCW, out, is going richer...
The needle jet is adjusted by varying the spacer thickness under the plate that mounts the needle to the slide... this has the biggest effect on acceleration and in the midrange area... Say 60+ mph cruising, and half throttle acceleration...
To test the main, accelerate from 30 or 40 mph, in 4th or 5th gear at full throttle for several seconds, then reduce throttle by about 1/8,...if power increases for a second, you are lean on the main jet. Go up one jet size and test again.
Jets are incrementally additive.... starting with the idle mix, then pilot, then needle, then main... Each jet adds it's volume to the next in line... Wide open throttle is accessing all of them, so changes in one, adds to next and the next..
I start at the bottom, and work my way up.... idle, pilot, needle, then main...