I have three genuine Honda motors that I regularly play around with. Two 8hp motors, and one 13hp. The two 8hp motors are on an offroad kart and motorbike respectively. I would like to add some personal experience to this question, as it may help others.
There are numerous mods that can be done to the Honda, clonda type engines. Removing the governor would propably be the first step, and in my case did add a slight power increase on its own, but nothing amazing. I dont have acess to a dyno, so just relaying how it feels when driving. I did however check the topspeed, and the removal of the governor did add a couple of mph.
There was no question of valve float at all. The next step was to advance the timing. Living all the way over in South Africa we dont get any of your nice add on performance parts, so I had to file down the key to be able to advance the flywheel timing to about 6 degrees. The results of advancing the timing was significantly better than just removing the governor. The motor was much more torquey, and acceleration improved significantly. Again there was a couple of mph diference in top speed, which would indicate an increase in overall rpm. There was no valve float with this modification either.
Next I took off the standard Honda exhaust, and built up my own free flowing one, capped off with a muffler from a big 12hp kohler that I had lying around. Besides it sounding a bit like a lawnmower, it actualy worked very well. Again there was an improvement in the seat of the pants power delivery, and throttle response was improved. Again there was no discernable valve float.
After all of this I got quite adventurous and pulled the head off to do some work on the ports. I propably spent about three hours working at it. I used the cheap option, a dowel with sandpaper wrapped around it to the right size fitted to a drill, and some round files. Smoothed out the finishes, and enlarged the ports slightly. Also increased the area where the gas curves towards the combustion chamber. I am sure that I may not have done the worlds best job at it, but once again the results were imediately evident. Better torque curve, developing power in a much wider rev range from much lower to quite a bit higher. Top speed again increased a little as measured with a gps on the go. There was still no perceptible valve float. The motor pulled strong all the way up to its max rpm, and could run there all day, and frequently does when me and the kids start playing around.
My las mod was to add the carb off of a 13hp honda to the gx240. Obviously it worked in conjunction with all of the other mods. The result is a motor which pulls like a freight train (compared to how it was initialy) We have our own track in our back yard.... big property, and in some of the places you cannot run full throttle anymore as the power just runs you right off the track.
After fitting the larger carb I have encountered some falve float, but only slightly. I can live with it for now. From spending much time on many forums I understand that I have propably reached the limit of what I can get from this motor without fitting a billet conrod. These are simply too expensive for me as your currency is currently worth 10 times what ours is. The motor is run extremely hard, often for hours on end, and it handles it all briliantly.
The modifications that I made are all within the grasp of the average guy, and they made a world of diference to the way the kart goes. It used to be a fun kart, now it is an adictive adrenalin rush. :biggrin5:
