Few questions on the AC 120 motor. I did get it running again after cleaning out all the garbage from the exploded gov gear and the adj main jet does make a difference.
I cannot seem to eliminate the bog when going WOT from idle. I followed the note that I received from recmotor on setting the main jet and saw (well, heard) a huge increase in rpm and it idles real nice, but when I hit the gas, it bogs, then it picks up. Subsequent blips of the throttle are fairly responsive, but if I let it sit and idle then open it up again, the same bog reappears.
Also, it appears I stupidly lost the little oring from the adj main jet. Any suggestions on what kind of shop I should hit up that would carry such a small oring (I've never shopped for one before and I'm sure there's no Orings-R-Us in town). LOL
Is it possible to bore and sleeve these 120's? It's '02 vintage. I haven't torn it down yet to make a really close inspection but I did observe and feel some scoring on the cylinder wall at the case end. I'm assuming the worst here and it might be fine and just need a new piston/rings (piston skirt had a chip out of it) but if I have to do some serious work, I'm wondering if I can, or should I just stick a replacement motor in it and replace the sled in time for next year (assuming my son wants to pursue snoX)?
Post by Bob Vehring on Mar 20, 2013 8:32:19 GMT -5
You will need to use both the idles adjustment screw and the main and work to find a balance point where you get the bog eliminated. Small turns at a time until it gets better then fine tune it. O rings you should find at any GOOD hardware store, or a lawn and garden shop that repairs mowers etc should have them. On rebuilding, yes it can be done like any engine. The proublem you might run into is that engine hasn't been built in quite a few years. A/C switched to a Yamaha engine in 2010. Even if found OEM pricing isn't cheap. A New Briggs engine is $505 and twice the power
Found the oring! Dug through the trash can where I'd been spraying carb cleaner over the weekend and it was sitting on a bag about halfway down. Thank the gods! I'm gonna try to find a little stockpile of those things.
I've been playing with the needles and have only been able to minimize the bog. Please help me to understand what causes the bog - too lean or too rich? I have operating under the presumption that it's too rich on idle that is causing it. What i did was to find the max rpm using the main jet. Then I leaned the idle to the point where the engine nearly quits, backed off enough to restore smooth idle. Even with the leaned out idle, it has that momentary hesitation when I snap the throttle open. Richening the idle makes it worse. Adjusting the main jet doesn't seem to help, only makes the hesitation worse. I've got it minimized but everything I've read suggests that I should be able to pin the throttle after idling and it instantly snaps to full power. Is that a realistic expectation?
I inquired today about the Briggs. I cannot use it in stock classes and there are unfortunately no plans for a Briggs class. Seems my only choice now, to compete next year, is to build the motor I've got. Is going over this motor and bringing it up to factory snuff something your shop can do? If you could pm me your #, I'd like to talk more on this sometime.