Farmall cub won’t run without choke then dies

[Mahoman]

Ok so I rebuilt my cub, all good, I have oil pressure no fuel leaks, and a new carb. It fires up and sounds great but it will not run without the choke on, the air cleaner isn’t on but I don’t think that matters, it will run for a little bit maybe 10 seconds then dies, if I open the choke I hear it sick tons of air and it dies immediately, if I constantly open the choke and close it real fast I can get it to run as long as I want, I replaced the carb main gasket because mine had a tear in it but that didn’t help, I’m inexperienced with updraft carbs but my understanding of them is they need excellent vacuum to run proper. Can I assume I have a vacuum leak somewhere? I have a gasket between the carb and manifold and the manifold gaskets are on, I’m stumped.

[ntrenn]

On mine it’s almost always a tiny obstruction in the main jet...the brass plug on the side of the carb. Copper wire is your friend.

[Bob McCarty]

If the new carb is aftermarket (Chinese) you probably need to open it up and set the float height and drop if you didn't already.

[Mahoman]

On mine it’s almost always a tiny obstruction in the main jet...the brass plug on the side of the carb. Copper wire is your friend.

I sprayed carb cleaner through it and it’s not blocked

[Mahoman]

If the new carb is aftermarket (Chinese) you probably need to open it up and set the float height and drop if you didn't already.

I didn’t know about that how do you do that?

[Bob McCarty]

Here's a link to a thread that explains it, scroll down to the post by Glen. Let us know if you have any questions. viewtopic.php?f=1&t=108364&p=859791&hilit=float+height#p859791

[Jim Becker]

Make sure the lever on the choke shaft is positioned correctly so the choke isn't working backwards. (Look in the intake and make sure the butterfly is open when the choke rod is forward.)

[John *.?-!.* cub owner]

Jim beat me to it, I was wondering about that also.Is it an IH stye carb, or a Zenith carb? Have you removed the jet on the side near the bottom (IH) to see if good fuel flow comes out, or the cap on the bottom rear (Zenith) to check fuel flow?

[Mahoman]

I don’t have the oil bath or the intake hose set up yet, I’m trying to make it run as is before I finish everything else. I don’t have the choke rod on it yet either I’m doing everything by hand yes the choke it closing all the way, I got it to run steady ish and took it around the yard as a little celebratory drive but it runs like crap, it’s insanely rich so much that black smoke comes out the stack and the throttle does nothing but increase the black smoke it’s doesn’t gain any rpm. This carb is a 30 dollar eBay carb should I just bite the bullet and get a nice zenith carb? I’ve heard nothing but problems with these cheap carbs. I took the main jet out and it has great flow there, stuck a copper wire through but it was already clean, put it back didn’t run, it had a orange gasket on it and I took it off so that only the aluminum washer was on it, was it supposed to have a gasket? I’ll try setting the float level next but I’m not sure how that would affect it... thanks for all the advise,

~Hayden

[Eugene]

Make sure the lever on the choke shaft is positioned correctly so the choke isn't working backwards. (Look in the intake and make sure the butterfly is open when the choke rod is forward.)

And make sure the throttle linkage is correctly attached to the throttle lever on the side of the carburetor and that the butterfly opens when the throttle lever is advanced.

[Mahoman]

Make sure the lever on the choke shaft is positioned correctly so the choke isn't working backwards. (Look in the intake and make sure the butterfly is open when the choke rod is forward.)

And make sure the throttle linkage is correctly attached to the throttle lever on the side of the carburetor and that the butterfly opens when the throttle lever is advanced.

Yep verified that

[Mahoman]

I just cleaned every orifice with copper wire and blew carb cleaner through too, I replaced the intake manifold gaskets and cleaned up the mating surfaces, I cleaned the carb so that you could eat off of the inside and checked the float, it was 1.4” from the top when it was fully closed. Is it gremlins?

[Waif]

Well?

Have you confirmed all valves are working correctly?

Gravity feed of fuel uninterrupted from inside tank and all the way into carb. with good downhill flow? (Some carbs have a screen where fuel line enters carb). Meaning , good fuel flow when line is removed from carb. and no clogged screen at carb?

Linkage adjustment follows whenever a carb is changed , but linkage beyond that linkage at carb needs to be functioning correctly too , so not to be arguing with governor. Or governor not being able to work linkage.

Running choke plate open and closed to keep it running , would seem to combat the governor running linkage instead.

[Mahoman]

Well?

Have you confirmed all valves are working correctly?

Gravity feed of fuel uninterrupted from inside tank and all the way into carb. with good downhill flow? (Some carbs have a screen where fuel line enters carb). Meaning , good fuel flow when line is removed from carb. and no clogged screen at carb?

Linkage adjustment follows whenever a carb is changed , but linkage beyond that linkage at carb needs to be functioning correctly too , so not to be arguing with governor. Or governor not being able to work linkage.

Running choke plate open and closed to keep it running , would seem to combat the governor running linkage instead.

If you mean the valve train then yes, I rebuilt the entire motor and had it machined, it has new valves, valve guides and springs and everything it’s got 120 psi of compression on each cylinder.

Yes, I restored the sediment bowl with a new screen and gasket, I get perfect fuel flow all the way to the drain plug in the carb there is no screen at the carb

I just cleaned the needle and seat

I haven’t touched the linkage or governor, there’s still the wire on the governor from the factory

[Mahoman]

How should I check the linkage?