Hey! just joined the forum. I have a few questions, well mabey more like need a few opinions. I have a vintage go kart with dual motor mounts and a flathead Briggs 5hp on it.i have no Idea what brand or model the kart itself is so I'll post pics later and see if anyone can figure it out, it does have some numbers on it and i believe it was made here in Michigan. Anyways, I ported and polished the engine, shaved the eyebrows, decked the head ( not sure how much lol) and cut a small fire slot in the head (not sure how much this did, just an old ford flathead thing).
Warning of caution, it's really easy to do too much to a flatty and end up losing power, especially if its an old one with a cast iron flywheel... a cast aluminum one will rev faster and higher (less likely to explode on you too)
It has gained significant power from stock but now I am looking towards a performance carb. My thought was a pwk 24mm with a Tecumseh intake I have. Would this get me some more speed and overall better powerband or should I go 21mm.
Considering a 5hp briggs flatty is in the range of 196-210cc a 24mm carb is going to be a bit big. I'd say 20mm carb is going to be your best bet, MAYBE 22 at the most (when in doubt, just match the intake port diameter)
Using a "motorcycle" type carb means opening it up to remove all the governor hardware and plugging the case... I mention this because I didn't see where you mentioned having done anything with that or not at first.
The kart tops out at about 36mph, but it accelerates pretty slow. Also, would a 212 header work on this engine or not?
Different (closer than 48mm) stud spacing so No it will not, iirc the common Briggs type 5hp spacing is 40mm with 1" pipe threads inside the port
I was warned about removing those threads because the exhaust port is already technically too big so you may want to consider making an exhaust by just using a black iron pipe.
Stick a 2" nipple in the port with a 45° elbow on the end, with another 45° and stick a sausage in it (a briggs lawn muffler)
Your acceleration issue could be the gearing, could be the tire size... never immediately blame the engine for performance issues because it will only ever perform as well as the running gear allows. Could be the clutch because AFAIK NONE of those twin engine karts were yard karts which means they got a bare bones centrifugal clutch, they like to be kept at high rpm. Stop and go, or low rpm riding will fry a centrifugal clutch fast and being geared wrong for terrain and usage habbits will fry one the fastest
I don't want to remove the governor right now because i dont feel like having the flywheel exploding like a live grenade lol, thanks in advance.
You can't swap the carb for any other carb except another lawn carb without deleting the governor. That applies to ALL small equipment engines used for karts.
As mentioned above if the stock flywheel is an old cast iron one (fins are part of the cast), they can weigh up to 12lbs iirc for a 5hp Briggs so it will hold the rpm from spinning up quickly, but the rotational mass will also keep it spinning instead of letting it idle down promptly once off the throttle.
You should consider a cast aluminum one to gain throttle and rpm responsiveness while simultaneously raising the safety threshold of when it may or may not explode.
Every flywheel is its own anomaly, I've got a stock 5lb cast iron flywheel on my built 208 (charing system requirement) and never fail to spin it north of 5k rpm every ride. That's the thing, some explode between 4k and 5k, most hold up fine to 6k or just over, and yet others might make 8-9k if you can get the engine to spin that hard
Someone else would have better info on what you can get away with and what would be best, but we need pics and better info on the overall set up you've got going to get the power to the ground.
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