Flathead Briggs 4hp

FWIW, the model, etc. is 112202-0516-01-83032903. Put it on a minibike for my kid 30 years ago, and it's been in storage for probably 25 years. In the idiocy of old age, I decided to make it run again. And it does, sorta. The carb was ruined, I guess from the "new gas." I found a carb on Amazon for about $20, and got it started. It idles and revs up, but open the throttle under load and P-u-u-u-h. I gave away my torque wrench, compression tester, spring compressor and everything else years ago. Oh, how I don't want to try to rebuild it at this point. Anybody know where to find parts for this particular engine? Everything I see is for the 5hp (which was too tall for the minibike). I used to love these old flatheads. Not so much right now. Sorry for rambling on.

Thanks for your reply! Drastic adjustment of the mixture screw either way has no effect. When I turn it over by hand I can hear it sucking and puffing, but it feels like low compression. I think the kid ran it in the dirt with no air filter. I took a picture of the intake port and looks to me like a rock went through there. It still starts and runs, gotta love an old flathead Briggs.

I'm guessing 2.5"...  If there's 3 longer ones, they go in the corner of where the exhaust valve is.
 
 

It sure does - makes me not want to know where it went. Now I'll have to take the engine out of the frame and take the head off, if only to see what it looks like in there.