My 13.5 ho b&s surges heavily but smoothed out when blade/ deck is engaged or when I apply choke. I've twice cleaned carbs and still now working. I ran in garage with no air filter to elimina

On ALL Deere riding lawn mowers, 1st, position the deck under the tractor. Depending on the belt drive: either PTO (the yellow button on the dash panel), or tension engaged-(a lever on the right side of the operator\'s seat), you loop the drive belt from the front of the deck to the pulley, always in the lower front area of the tractor\'s engine. If it has "beltguards" too close to the pulley, you must loosen the retaining bolt for the guard, it will allow the belt to squeeze by and onto the pulley. Then, 2nd but don\'t forget to retighten after slipping the belt on, push the "Deck heighth" lever fwd to drop the deck "hangars" at the rear of the deck into position to "pin" the eyelets with the supplied pins, washers and keepers: usually a cotter pin or a lynchpin that inserts thru a hole on the smooth bolt-pin. The easy part\'s over, but don\'t panic. 3rd, lift the front of the deck onto a block, allowing a heighth to apply the "adjusting rod" into the front of the mower chassis. Screw the retaining nut onto the threaded (long bolt) and remove the block. You\'re done. Next, and very important, RAISE & LOWER the deck, engage the belt tension, (here you may have to clear the area and start the engine to engage the PTO drive, if it\'s electronically controlled belt-drive), this assures nothing is "misaligned" or improperly positioned. Now, if the machine is on a flat surface, lower the deck to a point just above the ground and measure the distance in four (4) corners of the deck and record the ht. Make the adjustments to LEVEL the deck. Now you\'re ready to start the engine from the operator\'s seat, slightly increase the engine from idle to 1/4 throttle speed so that engaging the drive belt won\'t kill the engine. Ensure the belts run smoothly, the blades turn, and the engine doesn\'t "bog". Lower the deck to a desired cutting ht., now MOW the grass!

YOU NEED TO REBUILD YOUR CARB WITH NEW DIAGPHRAMS AND SEATS

It is not possible for the choke operation to be reversed by its design. You have created some other condition in the carb with incomplete cleaning or improper reassembly. Dissassemble carb and carefully inspect every piece for proper placement(right side up or down) and cleanlyness. Inspect the float and float level carefully.

The fact the choke must be 2/3 applied to obtain a smooth idle indicates not enough fuel is being supplied by the carb at idle speed. Applying the choke richens the air/fuel ratio.

I suggest you revisit the carb idle air/fuel jets, air passages and any adjustments as well as checking for intake air leaks.

When levelling the deck, rotate the blades so that the right blade has one of its cutting edges at or near the right side center of the deck. Do the opposite with the left. Measure to the blades from the level ground, not to the deck. Try leveling that way.
Gary

Typically a surge is caused by a lean condition. I'd say the float is set to low and this is causing the engine to lean out & when you apply the choke it richens it back up.and the surge stops.

Sounds to me as tho it might need a carburetor adjustment, providing there is an adjustment screw on the carb. Sounds like the engine is running a bit lean. Did this problem occur right after the carb cleaning, or was it there in advance? Is there a fuel filter that might be clogged?

Does it have a fuel pump or is it gravity fed? If gravity fed, when you rebuilt the carb, did you make sure that the main (power) jet orifice was totally clean? No varnish or residue in the hole. Pressurized air or carb cleaner spray into the jet is a good way to test flow restrictions. It sounds like a clogged main jet or a vacuum leak at the carb to manifold gasket. You might want to flush the gas tank and replace the gas cap also, as evaporating fuel over time will leave behind varnish deposits if the cap doesn't seal, even though it is a vented cap.

This is most likely a belt problem. Check the deck drive belt that runs from the mower deck to the engine it/s come loose and got stuck between the guides.