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Yes, it's drippy carburetor time again

Sun Feb 10, 2013 3:19 pm

Hello all! My first post (inquiry) on this site. Here goes...
Just bought a '49 Farmall Cub in seemingly great shape. When the seller started the tractor up for demonstration, it took a bit of hand cranking, but she eventually caught and performed well. I noticed a fuel drip at the bottom of the carb, and the fellow represented that this was normal. I'm thinking not, but what do I know? I bought her and brought her home and now I can get the engine to fire but not run. I have carefully rebuilt the carburetor, checked and adjusted the float (curiously, the instructions in the kit included a bad float spec. 1-13/16", not 1-13/32"). The result is that the fuel is no longer dripping but rather gushing out. I've checked the fuel level in the bowl with a fitting in the bottom drain and length of clear tube, and it's on spec. Thus the float and needle valve are working. In fact, when I drain and then close the bowl and reopen the petcock, no fuel drips out at all until I have cranked the engine. After the first cranking, it acts as though a siphon has been established, and the steady (fast drip) flow continues 'til I close the valve at the tank. I'm baffled. There is more to tell, but perhaps without going on and on, this is enough for some intrepid cub owner(s) to suss this out. The castings look to be fine... Thanks in advance!

Re: Yes, it's drippy carburetor time again

Sun Feb 10, 2013 4:01 pm

John, just a couple things that come to my mind that you may double check.

Confirm you know for sure the exact location of the leak, it is sometimes hard to tell where it runs from.

Did you check that the float is not restricted in its travel when the carburetor halves are put back together? Sometimes it can bind.

Also, did you use a thread sealant on the discharge nozzle threads (this must be done carefully and utilizing the correct sealant). The gasket under this nozzle does not always seal properly depending on the conditions of the mating surface.

Verify a proper float drop = 3/16

Re: Yes, it's drippy carburetor time again

Sun Feb 10, 2013 4:04 pm

The Cub carburetor is an UPDRAFT carb. Meaning, that vacuum in the manifold from the intake stroke, pulls the atomized fuel up into the cylinders. When you crank the engine and it fails to start, the excess fuel falls back through the manifold and into the carburetor. This is likely what's happening to yours. It is normal on a no-start.

Re: Yes, it's drippy carburetor time again

Sun Feb 10, 2013 4:09 pm

Don has a good point, if your Cub is hard starting, a tune up and compression check may be in order.

Re: Yes, it's drippy carburetor time again

Sun Feb 10, 2013 7:36 pm

John:

G'day to you and congrats on pickin up your new to you '49 Cub. In this instance I would tend to agree with Don that the excess fuel is from the no-start situation is the key to the dripping. I am curious as to what carb kit you used. If it is a Tisco kit or a Sparex kit then there will definitely be issues. If you used a genuine IH kit (not the off brand replacement) or the kits from Steiner then you should be ok.

One of the things I would check would be fire - are you getting spark from the mag coil to the cap and then to the spark plugs. If no spark or intermittent or weak spark, would suggest a complete tuneup - points, condensor and maybe plugs. The checkup itself would be a good idea in any case.

One of the very first things I recommend is that a new owner read the Owner's Manual - McCormick Farmall Cub Operator's Manual 5-1-49 and become somewhat familiar with your new tractor. Then after you have read the manual, print it off - go outside to the barn etc., and then become more familiar with your Cub with the manual guiding you through. You would be surprised the headstart this will give you. IH was very good in writing their Owner's Manuals and made sure pretty much everything a new owner needed was included. It may take a bit, so I usually recommend a nice comfy seat in front of the puter and a cup of fresh coffee.

Suggest that you also take some time and read the info at the links below:

Image to Farmallcub.com :big smile: Forum Family. And you have come to the right place for all things Cub related. If you click on the Site Rules, Regulations, & Important Information, it will point you to :arrow: the Welcome Wagon wherein you will find links to many useful sites and topics. One of which is the Cub Manual Server. Enjoy!.

Re: Yes, it's drippy carburetor time again

Mon Feb 11, 2013 7:07 am

Welcome to the forum. Yep, sounds like a rubbing float to me. But stay away from the temptation of pecking on the carb, they are really easy to bend in. Better to take apart and do all the adjustments. You didn't use a TSC kit did you?

Re: Yes, it's drippy carburetor time again

Mon Feb 11, 2013 8:56 am

Thanks, all.

I have my work cut out for me, I see. I'll post the results.
The tune up kit was from Tractor Supply, I didn't notice the brand.
Float travel and drop are ok. The "no-start" sounds correct; it explains why they put the drip vent in the bottom of the carb too...
To clarify the pre-rebuild situation, the carb dripped as soon as the fuel reached the carburetor bowl--no cranking required. Multiple issues?

Side note:
My cub came with many of the original blue implements. I'm feeling lucky here.... and I always liked the asymmetric design of the cub. Form following function.

Re: Yes, it's drippy carburetor time again

Mon Feb 11, 2013 9:18 am

John Wilkinson wrote:To clarify the pre-rebuild situation, the carb dripped as soon as the fuel reached the carburetor bowl--no cranking required. Multiple issues?

This indicates the possibility of separate issues. Does it still do this after the carb cleaning and rebuild? If so, I would look for a fuel leak at the fuel line inlet.

Re: Yes, it's drippy carburetor time again

Mon Feb 11, 2013 10:26 am

If prior to rebuilding the carb, a continuous fuel drip was realized when the fuel was turned on, this would definitely indicate fuel was not being stopped by the needle valve after the bowl was filled.

If fuel no longer runs out with the fuel turned on, it is highly probable you have solved the needle valve problem. Checking fuel level in the bowl with clear plastic tubing is a very effective method of determining if float height has been set correctly which you have indicated it has.

I would have to say the posts before mine explaining updraft carburator characteristics well explain why your gas is dripping from the carb drain.

Your starting technique has a lot to do with how much gas pukes from the drain. You have to remember the engine draws a fuel/air mixture up into the engine. When you stop cranking the gasoline in this mixture will condense back to a liquid and gravity allows it to run to the lowest point.

If you could crank the engine nonstop for an hour, you would realize only a tiny amount of drip if any. If you repeatedly crank the engine giving the starter a rest frequently, you are going to have a puddle on the floor assuming it does not start.

Hand cranking then taking a rest before spinning it again will definitely cause a puddle on the floor.

As the others have mentioned, its time to dig in to why its not firing because it certainly appears the engine is not starved for fuel.

Re: Yes, it's drippy carburetor time again

Mon Feb 11, 2013 11:16 am

John:

I thought I had mentioned it, but I guess I forgot. One of the things to do is to check the whole fuel circuit. As Don mentioned you could very well have issues as the Fuel Sediment Bowl anywhere from the tank itself to the outlet to the carb. Here is a thread that might be of use - How To Upgrade A Cub Fuel System. I admit, I am a little partial to it :big smile: - but there are some valid points to look at. If the valve is leaking it will either have to be repacked or replaced. Personally I really like the ball valve solutions. Sure deletes the leak issues at the sediment bowl outlet.

Re: Yes, it's drippy carburetor time again

Mon Feb 11, 2013 11:16 am

I had bad luck with a TSC carb kit--some parts wouldn't even seat into the carb threading. Another kit from another supplier solved my problem. After that I switched to a local IH dealer for new parts. To me (far far from being an experienced tractor mechanic...still learning and this is the place to learn!) --it sounds like the fuel needs something to stop it from flowing: needle valve?, threading on carb fuel inlet?, float adjustment/sticking?, gasket not tightly on?.

One more point, that Lazy Union Driver and others have previously made -- if you don't want the fuel to come back down the intake manifold and make that puddle on the floor (witness the holes in the snow under my tractor during the recent snowstorm here!): Consider a heater element in the intake water pipe--I've not done it but will attempt it this summer. Supposed to keep the block and intake manifold warm as toast...as others have said. A search of previous topics about this will reveal latest with photos by Lazy Driver.

Re: Yes, it's drippy carburetor time again

Mon Feb 11, 2013 1:06 pm

One thing I didn't see mentioned is that some gaskets for between the 2 halves are too wide and hit the float and prevent it's proper operation. That is to say it another way they stick too far into the bowl area.
Another thing to consider is the round gasket at the needle valve seat is the seat tight enough and is the gasket ok.

Re: Yes, it's drippy carburetor time again

Mon Feb 11, 2013 3:33 pm

The TSC kit has the wrong needle and seat for the carb. It won't even thread in fully, leaving a huge gap around the base of the needle seat where the fuel is probably leaking in.

Re: Yes, it's drippy carburetor time again

Mon Feb 11, 2013 11:16 pm

Wow, I used the TSC kit and it is leaking like crazy. I have used Steiner before and I think I will go ahed and get an kit and a float. man that sucks that they are that inferior
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