574 runs lean

I have a International 574. It has the C-200 engine with the Marvel-Schebler carburetor.

The problem:
It will idle fine and throttle up to about 1000-1500 RPM but much more than that it'll bog and die out. If I pull the choke to about half, it'll run up to PTO RPM and run like a champ but has a hard time idling like that. This leads me to believe that it's running lean.

I bought this tractor back in February, and it's ran fine all spring and summer long until two weeks ago when it just decided to do this out of the blue.

I've had problems with junk in the tank clogging the inlet to the sediment bowl so I flushed out the tank, and double checked by removing the fuel level float and inspecting the tank through that hole. No obstructions.

I've removed and cleaned out the sediment bowl and it's valve assembly, and replaced the cork gasket and screen.

I've removed and used compressed air to blow out the fuel lines from the tank to the fuel pump, and from the fuel pump to the carb.

I've pulled the carb, and torn it completely apart twice, removing all jets and little pieces - cleaning it all thoroughly both times. The second time I replaced the bowl gasket, throttle shaft seal, and the gasket between the carb and manifold.

The shut off solenoid seems to be working properly as I can flip the key and hear it click. I've removed it from the carb, and have seen it work as a double check.

I can crank the engine over and with the drain plug removed from the carb's fuel bowl, it will flow what I consider to be plenty of fuel out the bottom, so I'm positive the carb is getting fuel.

The idle mixture screw is set correctly and it idles around 650 RPM as the manual states.
The manual says there's a "main fuel adjustment screw" at the outer end of the fuel shut off solenoid but when I unscrew it to the recommended 4 1/2 turns, it falls out around turn 3. I don't think it actually contacts the plunger as the manual says it should when it's fully screwed in. It looks as if the plunger seats in the end of the solenoid fitting itself and the screw is just a small jet of sorts. When I took it out of the solenoid the first time for cleaning it was screwed all the way in and tight. I assume that's the way it's supposed to be because I've never messed with it and it's worked correctly in the past.

I've sprayed penetrating oil around the intake where it mates to the head to see if I have a gasket leak there and that makes no difference in how it runs.

That's pretty much all the information I can give at this point.
I'm at my wits end and am seeking advice from others.
Any and all help will be appreciated.
I can take pictures of anything you need if it may help in a diagnosis.

Thank you!

Your original fuel shutoff solinoid was probably replaced with a non-adjustable one: they decided after a while that no adjustment was needed.

Sounds a lot like a vacuum leak to me. Try spraying starting fluid rather than oil: it burns better. Also disconnect the pipe to the air cleaner (you have checked it...) from the carb and try putting your hand over the carb inlet.

I am not trying to sound smart here, but did you put the venturi back in when you reassembled it? The symptoms you list are exactly the same as making this mistake (don't ask how I know. . .) The symptoms are also, as John mentioned, identical to that of a major vacuum leak. Did you spray test around the carb to manifold mating surface? On a side note though, these tractors do seem to run pretty lean. I find that when it is pulling any sort of load, it requires up to 1/4 choke to get power. Ours has the replacement shut-off solenoid without a main fuel adjust, so the size of the main jet dictates fuel flow. The 544 uses the same engine with a different main jet. I have asked several dealer mechanics and parts guys the difference but none of them know. It could be larger, but I was never brave enough to spend the money to find out...

John,
I pulled the air filter and intake pipe off (everything was open, no clogs) and while idling, placed my hand over the carb inlet. It sucked my hand right to it and scared the crap out of me. :lol: With my hand still over the inlet, the tractor sputtered out and died, like I expected it to.
I didn't try spraying any starter fluid after that.

Chadd,
You're not sounding smart, and I gather you had that happen? I'm sure it's happened to others so why wouldn't you ask?
The venturi was in it when I pulled it apart, and I put it back in when I reassembled it both times. I am pretty sure the smaller end was pointing up towards the manifold when I took it apart, and I made sure to put it back that way upon reassembly. The small end did seem to be loose in the throat, I assume it's supposed to be that way.

I put a brand new gasket on the carb to manifold mating surface. I made sure both surfaces were clean and smooth before installing it as well. I used a razor blade to get the old gasket off and it didn't get hung up on anything, so I'd say that was smooth enough.

Also, I've never had to use the choke to get any power, only to get it started when it's cold.

From what both of you have mentioned I'm going to assume I have the newer non-adjustable solenoid.

I agree with the vacuum leak theory as well, but I'm sure not seeing where it is and why it just suddenly appeared.

As a follow up, I had installed the venturi and it's seating ring upside down.
The the venturi's big end goes up towards the manifold, and the seat ring will have to be flipped on the fuel bowl so it will bolt back together properly.

(quoted from post at 19:43:23 10/28/09) As a follow up, I had installed the venturi and it's seating ring upside down.
The the venturi's big end goes up towards the manifold, and the seat ring will have to be flipped on the fuel bowl so it will bolt back together properly.

Click to expand...

I've seen that happen before. The way you can always be sure that the venturi is in correctly is the part with the smallest inner diameter will always be where the main fuel jet ends. That puts the lowest air pressure at the tip where the fuel is drawn out.

At full load there is very little manifold vacuum. The decrease in size of the venturi causes the air to have to move faster at that point lowering the air pressure enough that atmospheric pressure on the fuel in the fuel bowl pushed the up the jet.

At idle or light loads there is enough manifold vacuum so the venturi is not necessary but without it the fuel flow will drop off just as the engine needs more. By using the choke you can create a vacuum in the manifold allowing the engine to still draw fuel out the main jet.