Need Engine Help -- Real Puzzler

A good running 2504 is now about to drive me insane and I think I'm missing some real fundamental understanding. My engine is consuming more fuel than I can get through the carburetor. In less than a minute, the carb. reservoir is emptied after starting the engine with the required float setting. The sypmtom that I can't understand is that while the engine is running there is a liquid being "blown" out the exhaust pipe that is a pitch black oily substance that I suspect is liquid gasoline mixed with carbon from a function within the engine. The carburetor has had every conceivable repair and test that I've been able to find and still I can't get the engine to run longer than two minutes and that's with choking beyond any useful purpose - It wont run that way anyhow.
I think I'm firing on all cylinders and the engine seems to have the required power it needs now after many, many hours of repairs and re-adjustment after a stupid move a couple of years ago. I mistakenly added diesel fuel to my tank from a mismarked gas can and have not been able to get the machine running successfully since. I just don't have the knowledge to get this one running after many sucessful repairs over the years. Please, your thoughts are greatly appreciated. John
 
My WAG is here. The fact that the engine won't run without choke yet empties the bowl faster than the tank can keep up doesn't equate with sense in my mind. If I forget to turn on the petcock under the tank (on a SA) I'm lucky to get 1 minute of operation with what is left in the bowl. I believe you have a blockage in the carb somewhere still, could be a faulty needle valve, or the screen is plugged.

As far as your oily substance, I'm going to guess this is actual engine oil (!)...have you done a compression test to make sure the combustion chambers are still intact? Its possible there's damage to the cyl head or valve guide or seal such that oil is running down around the exhaust valve(s) but not into the combustion chamber. But, engine oil mixed with gasoline lowers its octane rating bigtime....that's the primary reason oil bath air cleaners went out of favor after awhile, the pulled-in oil knock-limits the engine ahead of its actual limit of heat transfer out of the chamber....iow just a few drops of engine oil render gasoline much less combustible.
 
The "oil" is condensation from the exhaust, normal until the exhaust is hot enough to evaporate it off. Your problem sounds like the fuel is not getting to the carb from the tank.
 
You've beaten the carburetor dead horse, but it sounds like you haven't looked UPSTREAM of the carburetor! Check your fuel supply.

Take the fuel supply line off of the carburetor and aim it into a clean bucket. Turn on the fuel. It should run a full consistent stream of fuel. If it trickles or dribbles, you've got a blockage in the fuel line, junk in the tank blocking the inlet, a plugged fuel filter, or a plugged sediment bowl.

Next, set yourself up a "test tank" with an old tank off of a riding mower, snowblower, rototiller, etc., some rubber fuel line, and a short length of 5/16" brake line and the fittings to connect it to the carburetor. Hang it above the carburetor and hook it up. If the tractor runs then you know it's a fuel supply problem from the tank.

By the way, running for one minute you do not have any idea if it's making "requisite power." The tractor should sound SMOOTH, no sputtering or coughing, for the entire time it's running on the gas in the carb bowl. If it isn't there's a problem.

ALSO by the way, the only way the diesel could be affecting anything is if it's still in the tank and you're trying to run the tractor on it. Mistakenly putting diesel in the gas tank won't hurt a thing on these old gas tractors. They won't run right until the diesel is flushed out of the system, but no permanent damage will be done. So, probably the "boneheaded" thing you did was panic and start ripping things apart when all you had to do was drain the tank, drain the carb bowl, and put in fresh gasoline.
 
If you get a good flow from that fuel line put it back and take the carb.drain plug out and see if you get a sustained flow out it.
 

I also agree that it's in fuel delivery. As others have said, pull the line where it goes to the carb. check the flow. It should be a stream. If you have a steady stream then it's in the carb. Most carbs have a screen at the inlet. Check it for restrictions if your flow is good.

If the flow isn't good, then make sure to check your sediment bowl base. You can use blow gun with a rubber tip and backflow the bowl with the valve open.

One of those two things should get you in the right direction.
 
We had similar symptoms with a "D" John Deere. The carburetor bowl vent was plugged. Air would get trapped in the bowl, the needle couldn't close, and gas would pour through the carb. Even had the black oily stuff out the exhaust, a few times. Hope this helps.
 
If you pull the carb drain plug do you get a good steady flow of gas that will fill a pint jar in less then 3 minutes?? If you do not get that then you have a gas flow problem. As for the stuff blowing out the exhaust do you by chance have an over full oil pan and or maybe you have a mix of gas and oil in the oil pan due to a carb float sticking problems and gas fills the manifold and then works it way into the engine. Had a guy call me one time about an over filled oil pan and I drained 5 gal of gas/oil out of it due to a carb problem
 
If it has the electric main jet shut off it would not run if it was not opening up since it shuts off the main jet if I am remembering it right
 
Hey Matt, thanks very much and first I need to apologize cause I don't know how to list all the things that I've done along this long road back to good engine health. Without choking the carb at all it will run for 53 seconds but one day I was able to extend that time to almost two minutes by choking the engine severely which is only a point of fact cause it wasn't going anywhere anyhow. The engine was hardly running at all and it doesn't make sense as the choke would make her run rich emptying the carb that much quicker. When the engine dies it rolls to a stop just as when it runs out of gas. I immediately close the petcock and then drain and measure the amount of fuel remaining. About two shot glasses full. A full bowl is about 5 or 6. My float has been adjusted so many times I can't count. It is in good shape, doesn't leak and isn't stock against the side or center. I know the seat is allowing fuel in at a rate that should fuel a big truck but yet, I quickly run out. It just seems that the fuel disappears up the intake manifold and comes out the exhaust without getting burned. Is this possible? Your second paragraph is intriguing. Yes, the compression is each cylinder is between 135 and 145 and none show any leak down. Out of desperation, plugs, points, condenser, rotor, wires, distributor are all new. Cap is almost new.Ignition timing is right on the money, fuel tank is cleaned with new hose to the carb with in-line filter. I don't know what else to do.
 
This is a simple Zenith updraft without anything electric and doesn't even have a load adjustment needle, only the idle needle. I don't know what could be simpler and it did work fine before the diesel went into the mix. The entire tractor ran fine and I cant get it back to that? Somewhere I picked up a gremlin.
 
Loren, I don't know how to check the vent plug. There is no replacement in the Carb kit but I would guess that the cleaning would have loosened whatever blocking. I have used compressed air at the passages inside but not directly at the vent. Your explanation sounds very much like what might be happening. Very obsucre and not something physically straight forward - right out in front of my face. Thanks I'll check this out.
 
Never thought to check the oil pan. I've seen this happen on small engines, garden tractors, a couple of times. I'm gonna run out and check that right now. Could be! Thanks
 
If it is the type of carb with the cap/plug over the main jet pull it off with the gas turned on and make sure you get a steady flow of gas out of it. If you do not then the main jet is clogged up so yes it will not run long
 
Can you see the neck of the sediment bowl when looking inside the tank? I have had all sorts of stuff in a tank that shouldn't have been there, rags, sticks, you name it. My number one sediment bowl restriction? Bees and beetles. Somehow get into the tank, and are just big enough to get stuck in the neck of the sediment bowl inside the tank. Something to look at anyway. Champion plugs? Put C87 A.C. plugs in it. I wonder if you have one that isn't firing well, and you just don't notice it? Not trying to call you stupid. Had a neighbor that was mechanical, but could never hear his tractor missing.
 
Pull the air cleaner hose off the carburetorand try running it there may be an obstruction in the air system that may be drawing oil from the head or past the rings
 
You definitely have a fuel delivery problem. The carb/fuel line should supply enough fuel to the engine to run under heavy choke until all the plugs foul out from the rich mixture. How about the fuel are you certain that you got straight gasoline in the tank now? I have made many idiotic mistakes in my day and had to eat crow after I realize what I had done. Here's what I'll add, how about a breach between the intake and exhaust manifolds in the heat riser area? Just a thought. I hope to hear some replies from you on some of the other suggestions. You should start a new thread with the same subject. If you do I will link this thread to that one if I see it. Welcome to YT by the way!!
 
you mentioned in several replies about unburnt gas coming out the exhaust, if so it is flooding and with that amount it should not even run, but from time to time impossible things happen,we have an h farmall that ran like a champ when put it under the shed where it sit for more than a year,when we got it out to use it again it was flooding so bad it would bearly run, no problem just clean the carb wrong!! after the 3rd removal and every part cleaned and every port having a wire cleaner ran thru it and still no visible problem I went and got another old carb of the self and tore it down using it as a reference thinking I had missed something, no luck put it back together installed it on the tractor still flooding, for some reason even though I had pulled the choke a couple times before knowing that was contrary to the problem and it made no difference I held my hand over the inlet opening slowly shutting of the air flow and all of a sudden the engine leveled off, I won't go into the details of the of the problem but the fix was to screw the main jet adjusting screw all the way to the seat then back it out a 1/4 turn and the engine would run fair enough to rev up, while it was at full throttle I turned the screw about another 1/2 turn out until it started to run rich then in just enough for it to level off, it has ran fine like that ever sense even with the mixture screw in that close, I still think that a small hole (ie porosity) opened in the main jet porting to the float bowl was the cause.
 

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