Hi,

I recently worked on an old Lawn Boy made in 1973, Model 7262, with a D-600 engine. Although it started right up, I couldn't get the mixture adjustment quite right. Turning the needle on the carb all the way in (clockwise to seat it) produced the highest rpm. I couldn't lean it out to the point where the engine would begin to faulter. My question is what could have caused this? (I ended up leaving it at 1 full turn out). Thanks.

I wanted to keep the question short, but here are more details if it might help.

The mower's pull-starter assembly was messed up, but since it had been sitting around a long time (years I think) with gas in it, I decided to take the carb apart and clean it as well before even attempting to fire it up. No parts were replaced, and as I indicated, it started on the first pull (a bit of a miracle). But I couldn't adjust the mixture according to the book.

After sitting overnight, the next day I noticed it was leaking gas from the float bowl gasket (I hadn't used the fuel cutoff feature). I surmised that if fuel is leaking out, then air must be leaking into the bowl when it's not flooded, causing a rich condition. (To my understanding, the altitude needle regulates how much air gets to the float bowl, relieving the vacuum and allowing gas to be drawn up.) So I replaced the gasket along with the float, inlet needle and seat. I also carefully sanded down the ears of the bowl (where the screws go through) since they were warped and didn't allow for good seating of the portions of the bowl between the ears.

After getting it together and starting it up, same symptoms. I tried applying tape around the bowl interface to see if air was still seeping in, but that didn't seem to help either.

I also re-tapered the point of the adjustment needle a couple of times, from less blunt to sharper and back again, but no change.

During the initial process of cleaning the carb, the removable inlet to the main jet was plugged up, and I did use a metal wire to help loosen the goop up. I know this isn't recommended, but I just swished it around a few times and find it hard to believe that I changed the orfice diameter in any significant way. I probably should have replaced it anyway, but didn't.

Any ideas would be appreciated.

Jim

P.S. The mower cut through my lawn just fine. I used an oscilloscope to check the rpm, which isn't too accurate a method, but as far as I could tell was around 3200 rpm on the high speed setting.