960 carb issue

grandpa Love

Well-known Member
Got a 57 960 rebuilt the carb it was
missing several parts. Runs better
now just an odd thing going on. The
top half of carb sweats while it's
running. What would cause this? Our
640 doesn't do this. Also no matter
what I do it seems to run rich.
Plugs get powdery sooty fairly
quickly. Timing is spot on.
Mechanical advance is working. Any
ideas on any of this?
 
The "sweating" is due to humidity in the air condensing on the metal, which means that the temperature of the metal is very cold compared to the ambient temperature of the air. It is normal to have some temperature difference because the outside air pressure is greater than the vacuum in the venturi of the carb. Just like when you let the pressure out of an aerosol can and the vapors go from the high pressure inside the can to the lower pressure outside of the can the can gets cold. If the pressure difference is great enough things can actually get cold enough to frost up. Your carb on your 640 doesn't move as much air so the vacuum in the carb isn't as great as the carb on the 960, so the carb of the 640 is probably colder than the outside air but not cold enough to cause condensation. So the condensation could be normal, but the running rich sounds like maybe the choke isn't opening all of the way, which could also contribute to the condensation, as when the air flow is restricted the vacuum is stronger so the metal of the carb can reach a colder temperature.
 
Good explanation. Thank you. Will
check the choke tomorrow. Maybe that
will help the eye burning while
hooking up implements!
 
Choke is not stuck. All the way open. I've turned main needle to less than 1 turn out. Still blows black when you give it throttle. When I rebuilt carb the kit came from Napa. It didn't come with main needle and the old one has some pitting on it. Could that be the issue? Also air filter had a birds nest or something in it when I got it. Cleaned it out good but couldn't remove the wire cloth. Maybe somewhat clogged? Dunno if that would cause it to run rich?
 
Well. I dunno. Main needle in lean? Or out for lean? I've read dozens of old posts on here and still confused!! Thanks for help
 
Main adjust in for lean. Idle adjust out for lean.
Idle adjust doesn't seem to be your problem. Yet.
Does it do the same with the air cleaner tube unhooked?
 
Runs the same with air cleaner pipe
Un hooked. At a show today. Got lots
of opinions but no fixes. One guy
looked things over and said I have
wrong carb. It's a marvel schebler
765. Claims that's the issue.
Another guy said it don't matter
that carb is fine. Yalls thoughts?
 
Pull air cleaner hose, see what difference it makes.

Also, does it only puff black at throttle up or stay black. Staying black I rich, puffing on throttle is valve guide seals.
 
Drove it in tractor show parade today. My wife was following on her 640. She says it smokes black all the time and puffs good when I hit throttle. Did you see comments about having a tsx 765 carb on it? Guy at show noticed it. Another guy says that ain't an issue?
 
Pulled air filter hose off, no difference. Made a loud sucking sound. I was surprised at volume of air being pulled in there. But it still smoked.
 
So.. just for fun I turned main needle all the way in. Tractor kept on running and smoking. Ran for several minutes. I turned it off and restarted it -still runs. When we rebuilt card we got a rebuild kit for a ford 900 series and carb is not correct. Checked parts catalog and kits are different. Could that be thhe whoke issue?? My brand new plugs are dry,black sooty mess. Best way to clean em? Got about 2 hours on em. At least they all equally black!
 

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