Carburetor troubles I guess.

[thgrahamjr]

I have a 3hp flathead briggs that has been rebuilt and looks good. My question is: Can anyone tell me why my engine will not run let alone start with a brand new OEM stock carburetor and fuel tank for this engine BUT will start and run with an emission carburetor? (The reason I'm not running the emission carb is because it has no air/fuel mixture adjustment and I don't want to damage the engine by running it to rich or lean)

 

[Affair_driven]

I don't want to damage the engine by running it to rich or lean

You won't, as it is a 4 cycle engine.
Where are/is your needle(s) set now?
There is a minimum setting at which engine will start and run.
Needs to be tweaked from there.

 

[thgrahamjr]

I have screwed the needle all the way in and worked it out in 1/8 turns until the needle was completely out with no avail, I have took the new carb apart to ensure everything that was suppose to be there was there. The fuel tank is also brand new so no rust deposits blocking screens, I put fresh fuel in it, new breather and filter. I put a teaspoon of gas in it and tried to start it, I even went to the briggs website and looked up the proper way to set your air/fuel screw (which stated to start at 1 1/2 turns counter clockwise from the closed position) nothing doing. Now when I put the emission carb on there which also has no idle adjustment (carb came off a 3.5 flathead briggs that was designed to run a pump) it fires right up with carb choked and then runs fine off choke but sense I can't adjust idle I have to hold the brakes so it wont take off (Idle is set to high and can't change it). HELP!!!!

 

[Affair_driven]

Something you can try.
With needle removed, set choke to fully closed and throttle 1/2 open.
Hold finger over needle valve hole and try to start it.
This should force fuel in to carb.
If it fires up, replace needle and try again.