I'm 40, have two boys 12 and 6. Almost 3 decades ago as a kid around 14 years old I was into building up 5HP Briggs flatheads for my home grown go-kart. Sadly my stash of parts got lost in time. I started with cast off 5HP Briggs engines from the local ag operation that discarded them when they no longer ran well enough. The only aftermarket parts that I purchased was a Dyno cam (maybe it was a Crane? I don't remember) and a 3 stage header of some type I don't remember.
I don't know the specs on the cam, but I remember being amazed that the tops of the lobes looked like almost 1/2" of flat space. The valves came up, sat still, then dropped down when turned by hand.
I do not recall where I read it, but I got some pointers on how to make the stock carb perform better. The physical stop didn't let the butterfly valve open fully, so that was ground down. I pulled out the butterfly valve assembly and ground the threads of the screw sticking out into the airflow down, slimmed the stem down to an airflow shape, and port matched the carb to the head. I also ran a die grinder in the air passageways to enlarge them as much as possible, as well as made some attempts at cleaning up the head around the valve area.
Between all that and removing the governor my go-kart had noticeably better performance. With a stock engine I couldn't spin the tires on cement. After my "redneck tune up" it would actually leave a bit of a patch on a good day. I was thrilled!
I worked on a couple different kits, but I only had the cam and header on my last engine. As I mentioned, it ran like crazy, until it didn't one day. Of course I was running all stock internals, so that rod eventually got tired of screaming around at RPM's it was never meant to and it grenaded. I remember taking the side cover off and literally pouring out the rod in a pile. The biggest piece was about 1/3 of the bottom rod cap. My assumption is the high RPM was slowing fracturing that rod and when it let go it just turned to little pieces. I never built another one sadly.
At that time, I had no manual, the internet was just a dream, and so I just did the best I could. One one particular pull apart and re-assembly I accidentally swapped the lifters, not knowing they were different heights yet. Of course it didn't run right when I put it together. I must have pulled it apart 3 or 4 times that afternoon before I finally figured it out. On the last assembly I laid all the parts out on the cement and assembled it with my eyes closed, and it ran.
Now almost 30 years later, I am happy to see the activity on this thread. I have a couple old blocks in my wood shop, but I believe at least one is junk, and I wonder if the other one is a 3HP. It's past time that my boys begin to get greasy, and those engines are so good at teaching the basics.
I'm certain the engine I built wouldn't have won any real races but I know they impressed numerous friends.
I don't know the specs on the cam, but I remember being amazed that the tops of the lobes looked like almost 1/2" of flat space. The valves came up, sat still, then dropped down when turned by hand.
I do not recall where I read it, but I got some pointers on how to make the stock carb perform better. The physical stop didn't let the butterfly valve open fully, so that was ground down. I pulled out the butterfly valve assembly and ground the threads of the screw sticking out into the airflow down, slimmed the stem down to an airflow shape, and port matched the carb to the head. I also ran a die grinder in the air passageways to enlarge them as much as possible, as well as made some attempts at cleaning up the head around the valve area.
Between all that and removing the governor my go-kart had noticeably better performance. With a stock engine I couldn't spin the tires on cement. After my "redneck tune up" it would actually leave a bit of a patch on a good day. I was thrilled!
I worked on a couple different kits, but I only had the cam and header on my last engine. As I mentioned, it ran like crazy, until it didn't one day. Of course I was running all stock internals, so that rod eventually got tired of screaming around at RPM's it was never meant to and it grenaded. I remember taking the side cover off and literally pouring out the rod in a pile. The biggest piece was about 1/3 of the bottom rod cap. My assumption is the high RPM was slowing fracturing that rod and when it let go it just turned to little pieces. I never built another one sadly.
At that time, I had no manual, the internet was just a dream, and so I just did the best I could. One one particular pull apart and re-assembly I accidentally swapped the lifters, not knowing they were different heights yet. Of course it didn't run right when I put it together. I must have pulled it apart 3 or 4 times that afternoon before I finally figured it out. On the last assembly I laid all the parts out on the cement and assembled it with my eyes closed, and it ran.
Now almost 30 years later, I am happy to see the activity on this thread. I have a couple old blocks in my wood shop, but I believe at least one is junk, and I wonder if the other one is a 3HP. It's past time that my boys begin to get greasy, and those engines are so good at teaching the basics.
I'm certain the engine I built wouldn't have won any real races but I know they impressed numerous friends.
Thanks and God bless,