8N Idle Trouble

Here's what I've done: rebuilt carb., new points/condenser, new spark plugs, new ignition wires, new battery, new wiring harness (connections verified by OEM wiring diagram), cleaned air filter, cleaned fuel sediment bowl, removed gas tank and cleaned, removed intake/exhaust manifold and cleaned and leak tested after mounting, new proof meter.

All the above new material was bought at a New Holland store as OEM.

I've set the power mixture screw, then lowered the idle speed screw on the carb. However the idle mixture adjustment screw seems to have no affect at idle if I set it or bottom it out (550-600 rpm is as low as I can go). It does speed up if I completely remove the needle (throttle lever at same position).

Please let me know what I'm missing. Thanks much.

First do a thorough cleaning of the carburetor and replace the gasket between the two halves. Be sure that the float does not have any gas in it to cause it not to float properly.

The reason the carburetor may not want to idle is that the gasket that goes between the two halves of the carburetor is not sealing good. The castings are not finished too good to begin and lots of people damage the mating surfaces at the outer edge of the carburetor by banging on the side of the carburetor to stop it from flooding when the float sticks or there is foreign material between the needle and seat. (this treatment does work) :O) This gasket must be tight at the middle where the idle orifice gets it’s gasoline.
Remove the float attaching hinge by carefully prying it up until you can get a small screwdriver under it. Don’t bend the two small blind rivets. They will have to be re used to re assemble the float hinge.

Use a new sheet of 80 grit wet or dry sandpaper that is laid on a hard flat surface and lap both the mating surfaces until it is perfectly flat on both mating surfaces.

Re assemble the carburetor and you should be able to adjust the idle.

Adjust the idle by lowering the RPM and then turning the idle mixture screw in or out until the engine runs at the highest RPM. The RPM is what you will be listening for and not the way the engine runs. MAXIMUM RPM!!! At idle.

First let the engine warm up a bit. With the engine at full throtle,turn the main needle in clockwise untill the engine stumbles (not out) Then turn the main needle out until the engine runs smoothly. Reduce the throttle to idle and then quickly advance the throttle and see if the engine falters. If it does then open the high speed needle a fraction more and repeat until the engine will accelerate without stumbling. Reduce the throttle to a low idle speed. Turn the idle needle in and out until the highest engine speed is found. This is where to leave it, regardless of how many turns in or out. HIGHEST SPEED! Not sound of engine. The highest speed will be the best idle. Reduce the RPMs to where you want them after the highest engine speed at idle is reached when adjusting the idle needle.
To adjust the high speed mixture you should start the tractor with the high speed needle open about two full turns and allow the engine to warm up before attempting adustment of the high speed mixture. With the engine at high RPM begin to turn the high speed mixture needle in clockwise until the engine begins to falter. Be ready to use the choke to keep the engine running. Open the needle counter clock wise until the engine does not falter and then idle it down and suddenly accelerate by opening the throttle to full throttle. If the engine falter or hesitates you should open the high speed needle another 1/8 turn and try the sudden acceleration unit the engine does not falter on acceleration.

Just a thought.
Good Luck!

This assumes good spark, etc.

Have you checked for vacume leaks?

Soundguy