Idles fine but will not take throttle backfires spits. Seams to be leaning out. The jet that came with was a 39 we took it aprt cleaned it changed jet emulsion tube bowl bowl gasket. We checked the the low idle jet it was a 19 and the o ring was still in the carb. Checked adjustet and seat all good. Could it be casting problem? Help please.
This could be your problem, the o-ring should be on the low speed jet, not in the carb. It should have 2 o-rings on it, one on the top and one on the bottom. I would agree that it is most likely a jetting issue, if you have another ruixing carb that works great on the engine, try swapping the main jet, etube and low speed jet from that carb to the new one, and also check to see where the idle mixture screw is set at on the old carb and set the new one the same way, to find out where the idle mixture screw is set, screw in the mixture screw all the way and count how many turns it takes to get it all the way in, then set the new one the same way. Using an aftermarket air filter and small pipe, your jetting should be somewhere around .036-.39 main and .020-.026 low speed jets. We use the stock airbox and 3/4" weenie pipe around here, and our box stocks will not work with anything bigger than a 30 main and .022 low speed jet, but the aftermarket air filter should allow alot more air into the engine, meaning you can run a bigger main jet. Keep in mind, the bigger the low speed jet you use, the smaller main jet you will need, and the smaller low speed jet you use, the bigger main jet you will need, that is what iv found by tuning these carbs. The Etube you are using could also play a big role in what jetting you need and what will work. Try different Etubes and see what works best. It is not the carb that is the issue, it the tuning part that needs to be tweaked. I have rarely had any carb work perfect right out of the box without having to fine tune it to get the most out of it.
Also, is this a stock carb, blueprinted carb or what? You said it came new with a .039 main jet, leading me to believe its a blueprinted or aftermarket ruixing carb rather than a box stock pipe that comes on new motors, every carb i have bought new came with a .028 or .029 main jet and .019 or .020 low jet, other than the ones you buy blueprinted from people like Dover, those come with the bigger jets, also the ones from Box Stock Project typically come with a bigger main jet, i believe they come with a .036 main but am not sure.
