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carb problem 8n...

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Joined: 20 Mar 2012
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PostPosted: Sun Jun 30, 2013 6:31 am    Post subject: carb problem 8n... Reply to specific post Reply with quote

I have to choke quite a bit to get it started. once started it still don't sound too good. a lot of put,put. ive took carb apart and its extra clean. where it mounts to the intake is really cold and a lot of moisture on outside, maybe this is normal for cast ?? or a problem ?
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Bruce (VA)
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Joined: 24 Feb 2003
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Location: Old Church VA

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PostPosted: Sun Jun 30, 2013 6:41 am    Post subject: Re: carb problem 8n... Reply to specific post Reply with quote

It's called carb icing & is a natural occurrence driven by air temp & humidity. Make a carb heater out of tinfoil.

But that's not likely causing your problem.

While each N has it's own starting sequence, none of them will start well by just yanking out the choke rod & holding it out for 5 or 10 seconds while the engine cranks. This is an updraft carb w/ a gravity fuel system; it is by it's very nature subject to flooding. Too much choke makes it happen.

Try this:

Key on, gas on 2 full turns, clutch in, 3/4 throttle, press the starter button. Let it crank for at least 3 - 4 seconds before you pull the choke rod. Then, don't hold it out for more than 2 or 3 seconds.

If you find out it will not start w/o excessive choking, you have problems

Try adjusting the carb.

Make sure the tractor is at operating temp; that usually takes 10 – 15 minutes at idle depending on ambient temp.

Both Ford and Marvel/Schebler (assuming you have a M/S carb ) say to set both the side-pointing idlemix and the down-pointing mainjet to 1-turn as a starting point. I set the down-pointing mainjet to 1-1/2 turns and don't fool w/ it until the final step.

Then adjust the side-pointing idlemix for fastest idle; not the smoothest idle. Next, adjust the behind the carb idle-speed set-screw for very slow 400-rpms idle. Do that idlemix adjust for maximum idle at least 3-times. Make sure that you turn the screws slowly, like 1/8 of a turn at a time & wait a second or two for the engine to catch up. Take your time!

Do it like this:

1. Adjust idle mix jet until RPM increases

2. Adjust idle-mix set screw until the engine nearly stops (as slow as you can get it unless you have a tach that tells you 400 rpm)

Repeat steps 1 - 3 three times.

Remember the side-pointing idlemix is out for lean, in for rich.

If you do not have any problems inside the carb, it is easy to get the idle down to 350 - 400 rpms.

Your last step is to go back to the main jet. Remember, in for lean, out for rich. If you end up turning it OUT more than ½ turn for max power (remember, you already had it 1 ½ turns out) then stop right there because you have a dirty carb or a fuel problem.

Lastly, each of us has his own definition of a carb rebuild. If taking it apart & seeing that it was clean is all you did, that didn't get you much because you need to soak the carb 24 hrs in a bucket of caustic carb cleaner & blow out every orifice w/ a rubber tipped air gun.
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PostPosted: Sun Jun 30, 2013 8:40 am    Post subject: Re: carb problem 8n... Reply to specific post Reply with quote

Also check your points, rotor and cap.
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