Carb Issue?

Jim in Western MI · Oct 16, 2016

My "new to me" 1958 631 started fine and ran great since February when it came with a small farm. It is a powerful tractor in the mountains compared to either of the 8N's I have. It had not been run for at least a couple years. I purged the fuel tank, cleaned and checked the points, installed new battery and replaced corroded cables prior to trying to start it the first time. Since then, it started on the 3rd or 4th rev with a quick touch of choke. But this Saturday it started with difficulty and with great amounts of black smoke, ran very rough and cut off within seconds. Restarted the same way, lots of black smoke. Finally got it to run a couple minutes, stumbling much, and checked the idle mixture screw with no effect through several turns, beginning with one full turn from seated. Do you carb experts see what I could have missed? I think it must be a stuck or sunken float..., could be original from 1958, no way to know. Did some rapping on the carb bowl with no affect. Can the 631 carbs be rebuilt as easy as the N's? (I always wanted one of GB's or Royse's beautiful works-of-art anyway!)

Den N Ms · Oct 16, 2016

Jim,I believe that you may have it with the stuck or sunken float part.The float could have a hole or seam leaking and be filled with gas after setting dry,and not shutting off the needle valve.Time to take the carb apart for a look at the float.

Tall T · Oct 17, 2016

Jim,

Could also be a loose needle seat or the needle binding on the way to seating or just not seating true.

At times I decided for some reason to reuse what I had, I'd polish up the floats with fine steel wool (compressed air cleaning of course) and gently spin the needle tip a few times in 600 emery pinched into a V.

I'd also shine up the sides of the needle valve shaft and polish up the float tab where it contacts the needle.

Old gas especially or just long term use, leaves that obvious oxidized and non slippery residue whereas shiny brass is slippery.

Even if installing a kit I still try and make the floats look like new.

HCooke · Oct 17, 2016

"Can the 631 carbs be rebuilt as easy as the N's?"

Yes, the basics are the same. Different kit tho.

Royse · Oct 17, 2016

Yes, they can be rebuilt and if original, well worth it.
I'd be happy to rebuild it for you or help you do it yourself.
Either way.

Your assessment of a stuck or sunken float is a likely cause.
There may be others though. Is the choke opening correctly?
You may also want to try it with the air cleaner disconnected.
They can get clogged up and act as a permanent choke.

Jim in Western MI · Oct 17, 2016

Thanks so much! The choke has been and seems to be working normally. I serviced the air filter assembly several "run hours" ago and there were no problems. I would very much like to send this to you and know with confidence it will be done right! I rebuilt a carb long ago on my first car, a 64 Peugeot, but it was right in the yard so if it didn't work, I could keep on it..., though it worked the first time. This tractor is 4 hours away and I go there every 3rd week or so, and it is a royal pain to get there and not have it operational. Please e-mail me how you wish to handle it.

[email protected]

Thanks again!

Royse · Oct 17, 2016

Email sent.

Carb Issue?

Jim in Western MI

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Den N Ms

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Tall T

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HCooke

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Royse

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Jim in Western MI

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Royse

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