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SC40 seting up

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Les Littleton26/08/2008 21:45:00
120 forum posts
30 photos
Hi , can any one tell me how to set up my sc 40 carb . I am having trouble setting up the idle adjustment to get a steady tick over, I can only get a fast tick over which stops with one click of trim. The engine is second hand without instructions so i dont know the correct starting point for the idle screw.
simon barr27/08/2008 17:27:00
1039 forum posts
16 photos

Hello Les,

A fast tick-over and then stopping with one click of trim sounds more like the push-rod geomety is wrong. If the engine picks up from idle without either burbling (too rich) or cutting out (too lean), then the idle needle is about right. If the engine is rich on pick-up, close the idle needle a fraction and try again, and repeat this proccess until you get a smooth transition from idle to full throttle. Like-wise if too lean open the idle needle etc....

Hope this helps.

Steve Hargreaves - Moderator27/08/2008 17:29:00
6730 forum posts
191 photos

Hi Les...

Usual way is to open the main needle approx two turns, then close the throttle until it is about 1mm open. GENTLY screw the idle needle in until it seats. Then put a length of fuel tube onto the fuel feed & try & blow through it. slowly unscrew the idle needle until you can just hear a hiss of air & you turn a slightly lighter shade of purple .

Start the engine, turn for max rpm & then close the throttle......if it stops instantly its too the idle needle a 1/4 turn & try again. Once it will idle let it stablise for 30 seconds or so & then open the throttle. If it cuts dead its still too lean...if it splutters & smokes before picking up or cutting out its too rich. Adjust & try again.

Remember to keep all adjustments small & do them with the engine stopped. Not only will your fingers thank you for it  but you will inevitably move the throttle barrel during adjustment & make accurate tuning impossible......

Take care & have fun!!!

Les Littleton28/08/2008 19:37:00
120 forum posts
30 photos
Thanks for the help guys, i think i have it sorted now so its going up tommorrow evening for the best test of all.thanks again for the help..........

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