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Tractor Talk Discussion Forum

cub wont start

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javan

12-24-2007 12:40:49




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I just got done completely putting a cub together that I bought in pieces even the motor was torn down. I set the valves. I tried to get it running and with the choke about 75% on and the starter going all the time it acts like it wants to run. But when i let off of the starter it quits turning over. WHAT AM I MISSING TO GET THIS TRAC. GOING???? any help would be great!!!




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El Toro

12-25-2007 06:30:49




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 Re: cub wont start in reply to javan, 12-24-2007 12:40:49  
Are you sure you have the distributor or mag timed
correcly on No1 piston when its at TDC on the compression stroke? Pull No1 sparkplug near the radiator and place your thumb over the plug hole
while someone hand cranks the engine until you feel compression against your thumb. Have them to keep cranking slowly while you feel the compression. You need to look for your timing notch on your damper pulley when its aligned with the pointer. Then remove the cap on your distributor and see where the rotor is pointing. It should be at the No1 plug tower. Your plug wires need to be in this firing order as you view the cap too. Hal

2-1
4-3

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KEB1

12-24-2007 16:23:01




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 Re: cub wont start in reply to javan, 12-24-2007 12:40:49  
Start with the basics. An engine needs three things to run, fuel, compression, and spark in the right sequence.

Compression: Was the engine torn down far enough that the camshaft may be out of time with the crank? Pull the valve cover, take the spark plugs out, crank the engine over by hand, should be able to watch exhaust to intake transition (exhaust closing, intake opening) coincide with piston at top dead center on the exhaust stroke. If valve timing appears to be correct, do you have compression? Should run (poorly, but run) even with really low compression. If you have low compression, check to make sure the valve clearances are set properly so that they're actually closing.

Spark: Now that you have compression and have confirmed the valve timing, check the ignition. Do you have a spark? If not, check that the point gap is set properly. If still no spark, check to make sure there is power to the hot side of the coil, and that the points are opening and closing. If you connect a test light between the coil terminal connected to the points and ground, it will light when the points are open and go off when the points close.

If you have a spark, check to make sure its timed right. Bring #1 cylinder to the top of the compression stroke (put a finger over the spark plug hole to feel compression). Make sure the distributor rotor is pointing to the #1 plug wire position. If so, set the distributor timing so that the points just start to open at top dead center. The timing won't be exact, but it'll be close enough it should run.

Fuel: Now assuming you have compression and spark in the right sequence, check for fuel. If you crank for a while with the choke all the way closed, the plugs should be damp with fuel. If they're dry, check to make sure you have gas at the carb and the float level is set properly. You can also check for a manifold leak by putting your hand over the carburetor intake and cranking. If you don't get good suction, look for a leaking intake manifold (probably a gasket) that would make the mixture too lean to fire.

As I stated at the beginning, if you have compression, spark and fuel in the right sequence it WILL run. Maybe poorly, but it will run.

Hope this helps,

Keith

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leroy in ne

12-24-2007 14:00:57




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 Re: cub wont start in reply to javan, 12-24-2007 12:40:49  
new plugs? flooded? try drying spark plugs by removing and drying out with air hose or propane torch spin engine over with plugs out to clear flooding. check timing and firing order. open throttle slightly and give it a short shot of ether while its turning over. back to basics , air fuel compression and spark all at right time and it has to run



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trucker40

12-24-2007 13:18:02




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 Re: cub wont start in reply to javan, 12-24-2007 12:40:49  
Sounds like your ignition wire or switch or something is not working.
There is probly some way to bypass it just to get it hitting.I dont know what a Cub has on it but on my H its a push pull switch.Anyway its got to make a connection in the wire that goes to the coil some way.



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El Toro

12-24-2007 13:09:13




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 Re: cub wont start in reply to javan, 12-24-2007 12:40:49  
Has this tractor been converted to 12 volts with a ballast resistor? If it has, it could be a defective ballast resistor. Hal



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glennster

12-24-2007 12:55:19




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 Re: cub wont start in reply to javan, 12-24-2007 12:40:49  
assuming everything is set, carb, timing, valves ect, try pulling the spark plugs and give each cylinder a couple squirts of oil from an oil can. could be the rings are not seating yet and your compression is a little low. crank the motor over a couple times to distribute the oil, reinstall plugs and try er again.



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