Oh shit! you got it. We were scoping that in the swoop group. I dont think anyone was goin for it but thats a solid deal, and the elsuive 504/1C engine! winner winner
Effectively the "C" is a "D" cylinder, the higher power sachs version, but without the stroker crank that came with the D's. They never made the longer stroke on the 504s. BUT to the above point, it's effectively a D cylinder which means you've got a flat intake port as opposed to the "A/B" designations' angled intakes. This allows you to flip the intake forward for more room for bigger carbs (usually gotta trim some fins) or to rather easily stack a spacer under the intake to fit bigger carbs. The square bing is the stock one, but the jets are unique and the floats finicky and the size limited and the performance equally limited. standard round bing or SHA lets you get up to 15mm with the stock intake (which is 14.5mm ID) but for both of those you do need to space it up a bit. Also makes idles adjustments tricky w/ SHA cuz it's right against the frame but... whatever, worth it.
Dont get parts from '77, they really fell off and are extremely unreliable. doscycles is awesome and has bunches of sachs bits, treatland.tv is the other excellent goto.
see wiki for 505/1a performance: https://www.mopedarmy.com/wiki/Sachs_505_1a_performance . Yours is a 504 but most of the info is interchangeable
regarding the decomp, that's wrecked. the decomp goes inline with the starter cable and the cable squeezes it when you pull the starter. It's pretty unecessary, most people just remove it and block it offwith a bolt. more detail in the wiki above.
If you wanna repair it i'd just get a new one, any loss of springiness and bent bits in there it wont work right and robs you of performance
https://www.treatland.tv/sachs-decompression-valve-for-504-and-505-p/sachs-decomp-valve.htm
also needs probably a new cable, theyve got a specific end on there you can replicate it yourself or buy a new cable:
https://www.treatland.tv/SACHS-super-special-STARTER-DECOMP-cable-p/sachs-starter-decomp-cable.htm
personally I'd pull out the short section on that cable and block off the decomp.
regarding clutches, I'd probably just try it before messing with it. if it works it's best kept in factory mode. you can use ATF, just fill it in that side screw hole til it comes out. you might need to tilt it to get it thru the whole engine and refill back to the filler cap level.
also those lock in easy, use a big screwdriver that fits well, anything too small is just gonna mash it up and leave you needing a new one. they come in the gasket kits that treats and dos sell, but sadly looks like it's sold out...
https://www.doscycles.com/collections/sachs/products/sachs-gasket-and-seal-set
finally regarding new pipes, they dont stay on well with the header clamp-on setup. My favorite solution is to tack little rings to the header (washers or whatever) and drill little holes in the bottom cylinder fins and mount em together w a spring to help hold it up.
