A healthy stand of 10" grass will load your 8N but it should pull you through. It sounds like you have clogged fuel screens. Turn off the gas at the tank, pull the fuel line off the carb, remove the elbow, and clean or replace the screen. With the line open at the carb, turn on the gas at the tank. You should have a full-pipe flow out the line and nothing less will do. You may need to remove and clean the sediment bowl screen. If you still have low fuel flow you will have to empty the gas tank, remove the fuel valve, and clean the valve and screen. The valve stem comes right out so you can get it all cleaned up nice. When you reassemble the fuel line, a drop of oil on the nut thead will let you tighten the line for a good seal. Don't tighten either end of the steel fuel line until both ends are square fit and you can tighen the b-nuts with your fingers. It's easy to get the line caddy-wompus defeating a seal and maybe even stripping the brass threads.. Here's the set-up for the carb: Warm the engine to normal operating temperature. If it won’t warm up or maintain a constant operating temp then the thermostat might be bad or missing. To get the required 400 minimum rpm, back out the throttle arm adjust screw located on the backside of the carburetor. When you’re up against the stall, adjust the idle mix screw on the outside of the carburetor. Start at one turn out, screw in until rpm slows and then just back out to the higher rpm. Now go back to the throttle arm adjust screw and back it out to lower the rpm. Repeat the idle mix adjustment. Go back and forth like that until you have proven you cannot get a lower idle rpm. You cannot get the idle set too low. To set the main jet you need a load on the engine so you either jump up in the seat and apply the brake or you can put a heavy implement on the 3-point and engage the lift arms. Start at one-turn out and back it out until you can juice the throttle while loading the engine and the engine evenly takes-up the load.You get that done then perform the Hard-pull test: Idle the tractor in high gear and get her rolling forward just a little bit. Then quickly pull the throttle to 1/2 speed. Do this with your good brake partially on so that you have a heavy load on the engine. If the clutch slips then you’ll have to adjust or replace it. 1. Your timing is ok if you hear a constant slight pinging (spark knock). 2. If it backfires the fuel mix is too lean, the ignition is shorted, or you have sticky valves. Pull the spark plug wires one at a time and watch for a regular spark without a miss. You can hear sticky valves. Back out the main jet 1/8-turn at a time to see if that cures the backfire. 3. If it doesn't ping set the timing and make sure the mechanical advance is free to operate. A too long screw use in the points mounting plate can interfere with the mechanical advance weights. The weights may be dirty and sticky. 4. If it pings excessively then set the timing. If that doesn’t correct the pinging then pull all the plugs, clean them, and set their gap. While you have them out take a compression test on each cylinder with the throttle full open. The spec is 90psi minimum with 10% from highest to lowest. If you have 140psi then pull the head and remove the carbon. Make sure the valve stems are not gummy. Low compression indicates leaky valves, bad rings it’s a rebuild that isn’t broken in yet. 5. If the engine pulls evenly and there is no indication of late spark or excessive carbon, check the system for a lean fuel mixture. 6. If the engine pulls unevenly then check the spark at the spark plug boots. Watch the spark over several revolutions to see that it's a regular, blue, snappy spark and that it does not miss. You can do that while the engine is running.
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