Small Engines (Lawn Mowers, etc.): Lawnmower problems, throttle plate, fuel flow

Question
Hi Michael and thanks for your reply.  I am closing the carb tight with my hand.  This is the only way that the engine will start and stay running.  The only way that the carb will draw gasoline into it!! Please explain to me how to adjust whatever must be adjusted or fixed as I do not have alot of experience with these types of engines nor carburators.-------------------------
Followup To
Question -
B&S 3.5 HP old lawnmower. Replaced plug and oil. At first would only start easily if I held open the choke by putting screwdriver in throat of carb.  Removed carb and cleaned it.  Took out needle "screw" also and cleaned.  Replaced carb but now will only start if I put my hand on carb.  If I remove my hand engine dies.
Thanks in advance for any advice. Alan
Answer -
Hi Alan,

What are you doing to the carb?  Covering the inlet, closing or opening the choke?

The old problem sounds like the carb was flooding.

Michael

Answer
Hi Alan,

There is definately a lack of fuel flow to the engine.  You may just need to adjust the carb jets.  The large, high speed mixture jet is initially set at 1&1/2 turns out from closed.  The smaller, low speed mixture jet is set at 3/4 turn out.  The idle speed screw (Which stops the throttle plate from closing completely) is set to give a desired idle.  Some carbs do not have all these or even any adjustments.  If adjusting doesn't help, then there is an internal problem with the carb.   It will need to be dissassembled, re-cleaned and maybe a rebuild kit added.

Let me know how you make out.
Michael