I'll attach a copy of my dyno sheet in a minute here.... I have been getting pretty lousy gas mileage i think, and also my car feels a little gutless at the lower RPMs. When i stuck it on the dyno...well, you'll just have to see the a/f ratio for yourself. The black line is my first run, and the red is my second run. I picked up 7 horsepower with the jet change (went up two sizes), but i think something else is the problem here, and really i think it only put my peak hp higher, and probably made the rest worse. First of all, i changed my pump shot the minute i got home, and i think that ought to help with it going WAYYYY rich on the get-go. What worries me the most is it slowly leaning out (and me having to put a larger jet in to compensate). My guess is that my stock, mechanical fuel pump is not enough--but i wanted to ask you guys for your thoughts before i dole out my hard-earned money. Any other thoughts? The guy at the dyno "doesn't do carburetors", so i was on my own. Thanks! P.S.--the hp increase shown is actually due to timing changes...not jetting!
FWIW-yes, you're right in stating that your A/F is too lean. What kind of carb is it? Some holleys have adjustable air bleeds....but they are a "last resort" when it comes to tuning. First, you'll have to make sure your fuel system is up to the task. a good fuel pressure gauge will tell you if it's leaning out at higher revs. Be warned, however....you probably won't be able to see a drop in fuel pressure until it's in high gear and at an RPM near peak horsepower. You won't be able to see it in low gear, unless it's really severe. If the pump is up to the task, and there are no restrictions in the line between the pump and main jet (yes, I said main jet....sometimes the needle & seat assemblies will cause fuel starvation before the fuel even gets into the bowl, and this will not show up on a pressure gauge) then I'd try the air bleed adjustment. In short, the smaller the air bleed holes, the richer the mixture will be and vise-versa. But, like mentioned previously, don't mess with them until you're absolutely positive that everything else is OK. BTW, your A/F ratio should be around 12.5:1 for best power and torque, and 14.7:1 for best fuel economy. You wont be able to get a true 14.7 (or even halfway close) with a carburetor. Unfortunately, basically you just have some fine-tuning on your hands which is quite time consuming and potentially frustrating. You think this is bad, try tuning a carb with 15 PSI pressure running through it from a turbo. Carbs are designed for vacuum, not pressure!
