Trouble starting

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Trouble starting

Postby ESchellenberg » Thu Nov 19, 2015 3:33 pm

Hi everyone, new 1947 cub owner here. Started up great when I went to look at it, and wouldn't start after hauling it on a trailer for 4 hours. I replaced the old sediment bowl, and did a full carb clean and rebuild since it was leaking pretty badly. I put it back on and it started up perfectly. Went back a week later and it was having the same trouble, seemed like flooding. Gas leaking out of the air intake port on the carb, around the choke. After a little more cranking than I probably should have done, it fired up and ran quite smoothly for a while as I drove it to a new storage location for about 15 minutes. I closed the fuel line and let it run out to try and keep the carb from getting gummed up.

I figure this means maybe my fuel level is too high? Should I adjust the float level down a bit? Any reasons why it would be leaking around the air intake?



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Re: Trouble starting

Postby twotone » Thu Nov 19, 2015 6:53 pm

Both my Cubs run a little rich, and I rarely have to choke them, even if they've sat for several months. Mine flood real easy if they're choked too much. A quick pull on the rod and right back in, and sometimes that will flood them. If they flood,I just give it full throttle and pull the starter. They usally fire up fairly fast, run rough, then clear out the excess gas and run fine. I also shut the fuel off and let the carb run dry. My Super A starts about the same way.

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Re: Trouble starting

Postby Don McCombs » Thu Nov 19, 2015 7:16 pm

To add to what Tom said... The Cub carburetor is an updraft style carb. Vacuum created in the combustion chambers as the engine revolves pulls fuel from the carburetor, through the manifold and into the cylinders. In a non-start situation (whatever the cause) the fuel has no where to go, so it drains back down through the throat of the carb, causing the "leak" that you see. Perfectly normal.
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Re: Trouble starting

Postby Glen » Thu Nov 19, 2015 8:40 pm

Hi, welcome to the website.
I see you have rebuilt the carb. If yours is dripping when sitting, after rebuilding it, you might have got a needle and seat that is not sealing right, or the float level is too high, or there is dirt in the needle and seat, or more than one of those reasons.
Some of this rebuilding info below might be helpful for other people.

Usually if a Cub carburetor is dripping when the Cub is just sitting, and you aren't trying to start it, it is the needle and seat, at the float, or dirt in the needle and seat, or the float level is too high, or more than one of those things together.
The needle and seat wear out after years of use. I've had the same Cub for many years, and had to replace the needle and seat several times over the years. The last one I put in has lasted much longer, don't know why, but has. All were from IH, and Case IH.
Pull the 2 halves of the carb straight apart for 3 or 4 inches, the idle tube is easy to break off if you are not careful. It is fastened onto the top half of the carb.
Blow out the passages with air when it is apart. The dirt and goop settles in the bottom of the carb, and in the little passages. Be sure the passages are open and clean. Wear your safety goggles then.
Don't over tighten the 4 screws that hold the 2 halves together, it is easy to warp the top half where the bowl is. I think there are men on here that can straighten a top if it is warped, if they are still doing that service.
Here is a page from the Cub parts book showing the IH carb. Click on the pic makes it bigger. :) ... 012-12.jpg

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