I have an Echo leaf blower, model PB 260L, on which I recently replaced the carb. OE on this guy was a Walbro. It was running rough at higher speeds, and upon taking it apart to try and rebuild, I found corrosion on the inside consistent with what I determined to be corrosion caused by high ethanol fuel. I checked the spark arrester screen and changed the plug before getting to this point, FWIW.
OK, so I found a Chinese-made equivalent carb specifically designed as a replacement for the Walbro. I put it on, but cannot get it adjusted across all RPM ranges. It is running smoothly at low RPMs, but cuts out when I give it gas. I'm not experienced enough to know if the cut out is caused by a mixture too lean or too rich.
But there's one thing that confuses me here. On most every other 2 stroke carb I've messed with, there have been two carb screws to adjust. Once marked "L" for low speed, and the other marked "H" for high speed. I learned how to adjust carbs like this when I was a teenager working for a lawn maintenance company. There's a pretty good time-tested protocol to getting these guys dialed in.
This has one screw near the bottom of the carb, where the fuel line comes in that I figured is for fuel mixture adjustments. There is a second screw of a different size directly on top of the throttle body that is small enough to require the use of a jeweler's screwdriver. I figure this is for the amount of fuel that flows into the carb. I have never seen anything like this before, but I'm just a shade tree mechanic, and don't see a ton of different things as a matter of routine. I tend to learn how to maintain what I own, but don't have much opportunity to branch out.
At any rate, I can't find any combination of adjustments that makes this thing run at higher speeds. Does anyone have a basic outline of what I need to know to get this going? Do carbs of this nature have separate adjustments for high RPMs vs. low RPMs? I'm happy to buy a book if someone has a good reference. I'm only into the carb for US $40 at this point (plus my time of course), but if I can get this thing going again for this price, I'll consider it a DIY win.
It might take me a day or two, but I can post back with pictures and even a video of the motor running if it helps.
Cool, many thanks. That was my initial thought, but there seems to be no position of the top screw that is correct for higher RPMs. My rule of thumb has been take the screw all the way in and back it out two full turns to use as a starting point. I've done that and about every position in half-turn increments, and nothing seems to be correct. I suppose there is a chance that there is something else wrong, but I've not been able to find it.
The carb in question is almost identical to the one shown here:
