ORIGINAL: Ram Jet
I never had a Walbro carb apart but I probably will have soon. I picked up a 30cc Homelite line trimmer out of the garbage this summer. Your carb may be too small for your engine but I can see no reason why the high speed mixture can't be balanced. The small carb venturi may restrict the amount of income air but a simple increase in main jet size will balance your fuel mixture. You can achieve a balanced fuel mixture but maybe not at the volume you think the engine can handle. There are some advantages to an undersized carb in that the fuel will more than likely be better atomized by the increased airflow, the engine will be less sensitive to atmospheric changes and it will be easier to tune.
Bill
Hi Bill,,, Thanks for the response. I dont think the venturi has much to do with the jetting in the carb. Actual case in point. I could not get the high speed needle to richen at wot, on a 150cc engine with a wga-7 walbro, this was before any mods to the carb. I installed a wb-25 and got the high needle to richen the engine at wot, was testing for air leaks around the intake system, however there was no noticible increase in rpm, and the wb-25 has a larger venturi than the wga-7/9 at that point I started enlarging jets in the carb, it is responding well enough, so its still on the engine. Then I called walbro and was informed the wga-7/9 was calibrated for a 100 cc engine. The wb-25 is going to be installed on the engine, and I know it will work, because its already been on the engine.
Jack