Full choke or backfire

[961kyle]

Just got a B running but it only runs with pretty much full choke. If I go to far taking the choke off it backfires bad out the exhaust and will eventually kill. Have cleaned the old carb out and messed with the idle but still does it. Any thoughts Id love to hear.

The inside of the carb is in bad shape. Very pitted and I cant get the main jet out. Some other parts are bugered up as well.

Its a zenith carburetor.

 

[khouse6]

i took a carb off 8 times and cleaned it, before i got it to do good.

 

[Dave41A]

My H used to do that. It was the idle circuit. On the H (IH carb) the idle adjustment is backwards from others: "out" is lean, "in" is rich. You didn't say what type carb this is but what you describe is clearly an engine that is starved for gas on the idle side. It's either still plugged, adjusted wrong, or could have a manifold (vacuum) leak. I think B's had a mix of Zenith, Marvel Shebler, and possibly other carbs. Post what you have (or take a picture) and I or someone else can help you out with the details. Good luck, Dave

 

[the tractor vet]

No you think you cleaned the carb out , Taking four screws out and spraying choke and carb cleaner in it and blowing it out is not cleaning it . setting in a HOT Spa bath of nasty chemicals for up to 24 hours then going thru all the passages with number drill bits by hand and torch tip drill, then blowen out then you cleaned a carb. Rust , varnish , and god only knows what the GREEN SLIME ya find in them today is that sets up like concrete and has to be glass beaded out . Then you have cleaned a carb . And even i sometimes have one that sends me to the bottle .

 

[old]

When one cleans a carb you need to do these 5 steps

#1 soak the carb in a good carb cleaner for 12-24 hours.
#2 spray the carb off with canned carb cleaner spray.
#3 Blow out all passage ways with compressed air.
#4 poke out all the passage ways with a piece of wire or as I use a torch tip cleaner tool.
#5 repeat steps 2-4 four or 5 times

 

[rustred]

this is the stuff i use. it sure is not as strong as it used to be . u must rinse in cool water after soaking carb , soak overnight.blow out all passages and i spray either brake clean or wd40 and blow out to check passages. the stuff i used in the garage would clean stuff in an hr.and as vet said take your hide off. i make my own gaskets.

 

[Dave41A]

Just re-read--you said it was Zenith (I should have read more carefully). These are easy carbs to work on, but the idle circuit has very fine passages. It does not take much (even just a partial obstruction) to make the engine run too lean. So even if air blows through, it may still be partially plugged.

 

[560Dennis]

I recommend a .04 drill bit , put by hand twisting into the small a hole in the idles circuit.(above main jet which lead up to just above throttle plate. ) I ve
done that quench over night cleaning With gunk many times on the Zenith 386 carburetor. With zero success in my case , what that cemented sludge
was from sitting around is. I don’t know but it’s frustrating and took me years to get to the cause of a situation having to run at half choke.

 

[F-Dean]

Check to make sure you have the firing order in the correct direction - Clockwise vs counter-clockwise. If you have it in the wrong direction, 2 cylinders will fire
correctly and 2 will fire when the exhaust valve is open - backfire.
Yes, I learned this from experience on my F-30.

 

[bc]

(quoted from post at 10:20:16 10/15/20) When one cleans a carb you need to do these 5 steps

#1 soak the carb in a good carb cleaner for 12-24 hours.
#2 spray the carb off with canned carb cleaner spray.
#3 Blow out all passage ways with compressed air.
#4 poke out all the passage ways with a piece of wire or as I use a torch tip cleaner tool.
#5 repeat steps 2-4 four or 5 times

I like this answer but would modify it a little. On step 4 blow it out again with air. On step 5 I would change it to repeat steps 1-4 four or five times. Sometimes soaking and bread wire cleaning only gets the top layer of crud out of those body passages.

In the end, I ended up buying one from the YT site here.

I wasn't very good at making those carb gaskets which are expensive but my buffalo brand ball pein hammer didn't make very good holes. I've now read about ball bearings and paper hole punches to make the holes and having the right material. Have always used the gray material but it always leaves frayed edges which could leave small particles in the carb unless I could get in there and trim with scissors. I just made some extra gray gaskets for the hydraulic flanges on both sides. A hole punch and cuticle scissors cleans up the edges. Not sure what Rustred uses for gasket material unless it is a cereal box.

As an aside, I saw yesterday that home cheapo sells a 6 quart container of diluted sulfuric battery acid in the water pump section for 21 bux. May resort to getting some for the tough part cleaning. I have the muratic acid as I used to dump 2 gallons in the gas tank and filled with water to get rid of rust and then sprayed the insides with wd40 to seal what metal it would reach except behind the baffle. That was before I took it off and had it cleaned and coated at a radiator shop.

 

[mattofvinings]

I like to use something like Berryman's Chem Dip where you dunk the carb in a "gallon paint can" overnight, close the lid, then pull it out tomorrow.

I steal a wire from a wire tag to help.

Mig wire could be .023", .030" or .035" and if you take some time to remove the burrs from snipping it off it could also be used.