Author Topic: Getting more HP out of my BS-7  (Read 1076 times)

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Offline Olclops

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Getting more HP out of my BS-7
« on: July 30, 2015, 02:04:45 PM »
Hey guys,

   Now that I've fixed the fuel leak and petcock on my little 50cc 1963 BS-7, I'd like to try to get it running a bit better. It tops out at about 29mph, and that's downhill.

  So far I've tried: 1) Using better fuel and additive, 2) cleaning the tank and the carb, 3) raising the idle (it's so erratic though, I'm not sure i actually raised it. Clockwise on the screw raises it I think?)

  Anyway, so far no dice, stays about the same. I'm thinking it may be a compression problem. But before I mess with remachining the cylinder, I thought I'd ask you guys. Could it be something simple like the throttle cable needing to tighten? Or is it maybe that a 180 lb man on a 50cc machine from 5 decades ago just isn't gonna go more than 30?



Offline disc_valve

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Re: Getting more HP out of my BS-7
« Reply #1 on: July 31, 2015, 06:33:53 AM »
On any two stroke, the main things that will affect the running and top speed are plugs/timing and blocked axhaust.

The first is easier - fit a new spark plug and check the ignition timing. If the points are pitted, try a new set.

Remove the cylinder head and exhaust pipe, and check that the exhaust port isn't blocked with carbon. Scape off any carbon inside the exhaust port and on the piston crown while you've got access to it. Remove the exhaust baffle pipe and give it a thorough clean. B urn it out with a blowtorch to remove any oil and carbon, and scrape any remaining carbon form the various holes in the baffle pipe. Then have a look through the muffler with the baffle removed. You should be able to see a clean hole through the centre. Over a long period of use the  muffler itself will coke up and restrict the flow of exhaust gasses. If in doubt, get a long piece of 10mm studding and poke it through the centre of the muffler, using it like a file to dislodge any carbon.

With luck, that should cure the bad running. I've got no experience of the BS-7 myself, but a 4hp motor should top out at around 40mph.




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