I have some updates. I have a bunch of different hobbies I tend to cycle through (RC, wine making, guitar...) and I haven't worked on this for a while until recently.
A while back I discovered some problems with the Briggs engine I used. Specifically the carburetor. Briggs designed this carb so it pretty much could not successfully be used on a moving vehicle.
The problem is that it has no external overflow vent. The vent for the bowl feeds into the intake of the carb. So if you hit a bump it vents extra gas into the intake and floods the engine. It works great on smooth ground, but as soon as you go on bumps it bogs down and sometimes stalls. Not good for an off road go kart.
To solve this issue I bought an XR50 clone carb and air filter on Ebay. It's a 22mm slide carb which is larger than the stock carb, so maybe it'll even have a bit more power. But I'm not changing the exhaust so maybe not.
I had to do a bunch of modifications to make the carb fit and I'll post some pictures later. Luckily the intake port on the head is large enough, but there is a plastic spacer I had to bore out to 22mm to match the new carb. Also the old carb bolted from the front and this one is designed to bolt on from behind, which is impossible without an adapter. So instead I used permanent thread locker to put bolts on the engine, and then I had to drill out the carb bolt holes slightly closer together and larger so they would line up. I also had to modify the carb by using a dremel so I could fit nuts on the flange to fasten it to the engine.
After all of this I've fired it up and it actually runs! It seems to run really well, idle is solid but I haven't had time to take it for a spin yet. I'm just happy that it fired up because I figured I'd have to change jets on the carb which I have no experience with. I still have to do plug readings to make sure it's not running too rich or lean but I'm pretty sure I can adjust this carb to work well. Luckily there is a
guide online on tuning a similar carb that I can work from.
