Engine bogs down when speed is increased.

Here's a possible solution to your tiller problem. Had the same issue with my Honda tiller. I cleaned and replaced every part I could think of with no success. I then discovered a small filter screen inside carburetor opposite the fuel inlet and next to diaphragm. Pulled it out with needle-nosed pliers and discovered gunk and trash underneath that was preventing a good gas flow. Cleaned it out thoroughly.and replaced the screen with a new one.Tiller runs like a top.

Ok I have r Royobi Tiller (30CC Gas) And last year it ran fine after rebuilding the Carb. This year it was "hard starts" Idles fine, (Tiny whisps of blue smoke in exhaust with correct ratio) Even seems to run better with the choke "on" but still...at idle only. as soon as I touch the throttle...its bogs down in tune with how much gas I give it. Little throttle? Little bog down, Little more throttle? Almost stalls, a normal throttle rev? it stalls dead! Then starts right back up again in 1 pull and idles fine again!? WTF? So after cleaning a clean carb again, (twice) and seeing no change I thought I'd go look at the original diaphragm and compare it with the rebuild kit diaphragm (which is the one in the carb.) And guess what? The replacement has a larger rivet by a factor of "2". So basically it was flooding the carb, I bent the needle tang down, better but no cigar. But I could rev it half way now. A second disassemble to bend it yet a bit further and Vrooom vroom vrooom ****! So check your needle valve even though you think its 100%. (Especially if you rebuilt the carb with a kit!)