Re: 9N runs rough

Posted by Rob on May 24, 2005 at 05:52:15 from (63.245.133.41):

In Reply to: 9N runs rough posted by Tracy (Go Vols) on May 23, 2005 at 19:13:12:

Fix the mainfold leak.

Running hot can be lean fuel mix.

Swap 3 & 4 plug wires at the distributor to check if you have that wrong.
Bend the spark plug wires and replace if they show surface cracks.

This will tell you want for:

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.

Adjust carb:

You may have to start with both carb jet adjust screws out 1-turn. The book says set the idle at 400rpm but the 2N doesn’t have a tachometer. You need 400rpm because the idle mix set-point is subtle and just near impossible to detect at a higher rpm. 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 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 proved you cannot get a lower idle rpm. You cannot get the idle set too low. One guy finally got his idle minimized and he posted it sounded like he could grab the fan blade to stop the engine. That’s what 400rpm sounds like.
I can"t tell you how to know you have the top speed set at 2200rpm except to say 2200 hundred is just only starting to sound like it"s running too fast to not be loaded. You adjust that after you make sure your governor arms can travel to that speed. Then you bend the control linkage between the throttle and the governor. Primitive eh? I don"t think that"s a huge deal because you want to operate at 3/4-throttle anyway. Belt-speed is near top end but if you have a belt you can set the top end according to the belt-driven tool performance.
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 ¼-turn at a time until you can juice the throttle and the engine evenly takes-up the load without hesitation. If it puffs a bit of smoke when you goose it then turn the screw back 1/8-turn.

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