I replaced a carb and steering gear on my friend's LA105. Ugh, the LA models are junk! After replacing the carb, spark plug, filters, etc. I washed it and cleaned it up pretty good. I went to test drive it and the engine performed okay, it seemed to be a little rich but I'll adjust that. 1st and 2nd gears were fine, 3rd was sluggish at first, 4th barely moved from a dead stop and 5th gear wouldn't move at all from a dead stop. I could run it in 3rd and shift to 4th and it would work up to speed and then I could shift to 5th on the run and it would work up to full speed, but from a dead stop no 4th or 5th. I suspected the drive and belt it does seem pretty slack but he said the drive belt is 3 years old with average use. The transmission did not have these issues before the carb and steering gear fix. What could have happened? I'm ready to set the thing on fire.