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Needles and seats....

D

Dave H (MI)

Well-known Member
I have this long term project in a 1957 Cub Loboy. I rebuilt the carburetor about 10 years ago. It has maybe 2 hrs of run time since. Giving me fits today. I chased down a vacuum leak that was a problem and it seems to be all good. Today I was testing it and it startes this AM cold with very little trouble. When I put gas in it there were no leaks. Later I put more gas in it and it immediately started dripping out the bottom of carb. Later still I put gas in it and no leaks at all and it started up first try. Gas is coming from a spotlessly clean temporary tank that I use. Is this likely to resolve thru use or should I just pull the carb and replace the needle and seat? I have heard of "break in" periods on these. It is one of the new needles with the plastic tip.
 
Just shut off the fuel every time you stop the tractor. It is by far the best practice. it might stop doing it, but it can't do it if shut off. Jim
 
If it stopped dripping, I would give it the benefit of the doubt that whatever was causing it has passed.

It only takes a microscopic piece of trash to hold the needle off the seat.

Another trick, drain the carb or run it empty with the fuel valve off. That will let the needle drop, the flood of fuel when the valve is turned on may wash out whatever was in there.

If the flooding continues, then go back in. Check the float, give it the "shake test" for fuel inside one of the pontoons. Check the float level. Clean the seat with a Q tip. Incpect the needle with a magnifying glass. With the upper housing inverted, the weight of the float resting on the needle, suck on the fuel fitting, put your tongue over the hole. It should hold vacuum. If not, there is a leak somewhere.

When I get the carb back on, I like to flush the line with gas before connecting it. Turn on the fuel valve, let gas run through the line as it is connected. This is especially important on a working tractor that is less than sanitary, or one that the fitting is difficult to see or connect.
 

Those viton tipped needles aren't very well liked. Many guys will put the old brass one back in.
 
as other said a little piece of dirt is all it takes to make it leak, additionally if you rebuilt it 10 years ago you may have components in your fuel system that don't like ethanol and if you aren't real careful about your fuel, or the folks you buy it from aren't, you may have ethanol in placed you don't think you do. Ethanol is a much better solvent than gasoline so much that it tends to dissolve things and turn them into little pieces of junk that can cause a needle valve in the carburetor to leak, it also produces some of the most remarkable corrosion.
 
I started reusing the original needles at some point. Had more trouble with the new ones and never seemed to be a problem if I just put the original back in.
 
It hasn't had any fuel in it but for the couple hours it was being run. Currently it is being fed from my temp tank and it is about as clean as it gets. I don't think it is foreign material, but I am keeping the option open. Could be some used teflon tape or such and bits are slowly coming off...or something similar.
 
I have been in and out of the carb a few times. Checked the float, adjusted the float with a micrometer, cleaned and checked the seat and needle. I am thinking since it is intermittent that I need to let it work a while and see if things change. Meanwhile, I will do what Jim N suggests and shut off the gas when it sits.
 
The way to test the needle and seat is to remove the carb , blow into the fuel line and flip the carb upside down and it should shut off your wind. If not needle leaks.
 

Dave, what do you mean by "dripping out the bottom of the carb" what point in the bottom is it dripping from?
 
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