Rough idle issues; suggestions?

[B3.3T]

M151A2, starts, runs great, just does not want to idle well. Leaving choke out a bit only helps a little. Airscrew?

 

[Snoop]

What means "does not want to idle well"?
Is idle to low, do it need more rpm?
Or does idle go up and down?

If idle is to low, turn the "idle-adjust-screw" a little clockwise.
See red arrows on the picture / forget the yellow arrows...


Ciao
Snoop

 

[B3.3T]

Thanks. That helped, but now the screw is bottomed out and could use a bit more. I guess I'll try a longer screw.

 

[papakb]

If the screw is bottomed out you don't need a longer screw, you need to identify where your air leak is and then fix it. Use some carb cleaner and shoot it around the intake manifold. When the engine speed changes you've found your air leak. Don't forget the PVC valve feeds into the intale too.

Kurt

 

[WillWagner]

^^^ this, or the carb is gummed up. Don't forcefully bottom the screw, you'll mess up the seat area and then you'll be needing a new carb.

 

[JGBallew]

Thanks. That helped, but now the screw is bottomed out and could use a bit more. I guess I'll try a longer screw.

If it's bottomed to get things to run, you have other issues. Remove the screw, and look for damage to it's tip. If it's damaged, you might try a new one.

If it's flooding at idle, check the fuel pump pressure. I've seen some cases where the return line orifice is too small, and the pump is forcing the needle off the seat.
You could try a different return line port, use wire gauge drills to incrementally open it, or install an aftermatket pressure regulator.