Craftsman LT4000 Carb Rebuild

After mowing the lawn once since the mower rebuild the thing started running absolutely horrible. The motor was revving up and down over and over and I just could not get it to stop. Every time I would get it to stop hunting it would just start hunting again. I searched the Internet and I couldn’t find any information that was useful. I couldn’t seem to figure it out for the life of me but one thing I did notice was that no amount of carburetor adjustment made any difference. This spoke volumes to me and since I already had the carb rebuild kit on hand I decided (although I didn’t want to yet) rebuild the carby. I ripped into the old carb and I have to admit it was quite fun working on one of these small carburetors at first. Then I noticed the new kit came with a brand new float needle seat. That’s right, not just the float needle but the copper plug that it seats into as well.

So I immediately think to myself “self, yes self?, this can’t be that hard to replace if they give you a new one right?”. Stupid self was completely wrong and I ended up drilling the damn thing out praying the entire time that I would drill to far or over to the side to much and find myself on Sears Parts Direct buying a whole new carburetor. I was lucky and pulled it off but after I got it all back together it was running worse than before and again no amount of adjust would fix it. I started looking into other things like the fuel filter and lines to make sure they weren’t pinched. Everything was brand new but after the recent work I didn’t know what could have happened. I decided later that night I would rip into the carb again and give it a once over. While I was in there I noticed the float needle was getting stuck because the new copper sleeve was slightly out of round near the top edge from pounding it in. I used a drill bit to put it back into round and threw it all back together after another carb bath. The next day she fired right up and started running like a champ after a little adjustment. I was now able to get the mower to idle at the lowest possible speed without any hesitation, hunting, or other unwanted side effects.

Later I purchased a laser digital tachometer and checked the RPM of the motor at idle and full throttle according to specification and surprisingly when I originally ball parked the motor I was damn near dead on. Check out the attached gallery for some picture of the process and although I am not including a full write up on how to rebuild your Craftsman Carburetor (there are plenty out there) the pictures should help show you what to expect. While I was at it I fixed the headlights. I included those pictures as well.