carburetor question

[DrPizza]

I suppose a carburetor is a carburetor. Mine's attached to a tractor (Allis Chalmers D-15, if that matters.) Carburetor is either a TSX-815, 844, or 869 (I can inspect it if it makes much difference; they're all almost identical.)

Anyways, the tractor runs great, at first. Gradually it starts not running so good unless I start choking it. Eventually it only runs with the choke closed, but runs okay like that. Occasionally, if it's been running a little rough and it stalls (like I put it into 4th gear holding up 400 pounds in the bucket) I have trouble getting it to start back up. My brother showed me a trick to pull the hose off the air intake & cover it with my hand, allowing suction to build, then releasing it quickly. A couple times of doing that and it usually starts right back up.

However, when I pull the hose off the air intake - when it's been running rough, a small quantity of gas flows out I don't think it should. It normally doesn't. I'm guessing something is up with the float?? I took it apart & checked to see if there was anything obviously wrong - i.e. if the float was stuck or something. But, other than removing the top half from the bottom half, I don't dare fiddle with all those valves and needles (idle mixture needle, high speed mixture needle, inlet needle, or whatever else.)

I'm guessing the float is being allowed to go too high & gas is spilling over from somewhere to somewhere else or something. I have the shop manual for the tractor. Of course, if I had the LP model or the diesel model, it goes into great detail about how to adjust it. But for the gas model, all it says is "Float setting should be 1/4 inch from nearest face of float to gasket surface of throttle body with needle closed." Which way is closed for the needle? Which needle?

Any carb experts around here? I don't want to just fiddle with adjustments without a clue what I'm adjusting, which way, or why.

Thanks!

 

[boomerang]

I think your diagnosis is incorrect. You state that you must choke the engine to get it to run. You are artificially richening the mixture to keep it running. Your problem is not too much fuel, it's too little - but in this case, it's too much air.

But I don't think it's the carb. I think you have a vacuum leak that presents itself as the motor heats up. I would carefully check the intake system after the carburetor. Gaskets between the carb and manifold, and between the manifold and cylinder head. You may even have a cracked manifold with a crack that opens up as the manifold heats up.

Nothing wrong with checking the float level though. There is a needle valve attached to the float. It regulates the level of the gas in the float bowl. Remove the carb and then remove the float bowl. Tip the carburetor upside down to check the level. The distance between the float and the body of the carb should be 1/4". If that distance is too great, the engine will run lean from too little fuel. If it's too small, it will run rich from too much fuel. You would be looking for a gross discrepancy. A small variation in the 1/4" dimension is not going to have a big effect.

You may want to remove the float and check to see if it is saturated with gas. Shake it to see if it contains gas. If so, replace it.

But, as I said, based on your description, I think you have a lean condition that comes on as the engine warms up.

Edit: This is a picture I found that identifies the parts involved pretty well. It shows the float and the float needle.

http://ffracing.net/gallery/albums/Faded/floatlevel1.jpg

The tang is what would need to be adjusted to change the float level. You don't need to mess with any mixture screws or anything else. Once again, I don't think this is the problem. I just included this for educational purposes.

 

[DrPizza]

Thanks, will check those things now. Time to dump more gas on a tree stump.

 

[boomerang]

You can check for a vacuum leak fairly easily on that tractor if you have a propane bottle like is typically used by homeowners for soldering pipes. With the engine warmed up (when the problem occurs) crack the valve open and with propane flowing (not lit!) move the nozzle around the area where you suspect a leak. The engine speed will increase when the propane is sucked in. You could also use a spray can that dispenses anything flammable.

I say it should be easy, because tractor motors are pretty simple and everything is usually pretty accessible. Outside on a windy day will make it mission impossible though.

http://www.bernzomatic.com/products/product-detail.aspx?xmid=6961

 

[DrPizza]

Brilliant! Now I'll have to wait until it heats up again to check that though. Probably will check tomorrow morning when I'm digging postholes.

Not going to hurt anything with the choke mostly closed, am I?

 

[boomerang]

Brilliant! Now I'll have to wait until it heats up again to check that though. Probably will check tomorrow morning when I'm digging postholes.

Not going to hurt anything with the choke mostly closed, am I?

Well, no. My biggest worry would be having it run too rich and fouling the plugs - which is not really a big deal. If it's not huffing black smoke out the exhaust, I'd say you're fine.

The other consequence would be a loss of power because with the choke closed, you're not passing a lot of air. It may not rev freely and may bog down with a load on it. I'm sure there's a governor involved which will try to maintain an RPM by modulating the throttle plate. The closed choke is only going to allow so much air through in a sense negating the throttle. (It sounds like you're already having this problem - 4th gear, a lot of weight in the bucket.)

Hopefully I described that well enough.

 

[boomerang]

Just did a little research. It looks as though the intake and exhaust manifolds on that tractor are actually consolidated into one casting. I would not be surprised if it's cracked. But it might also just be that the mounting bolts are loose. It looks like the intake is through the 4 center ports. Only two of those ports have mounting holes, two each for a total of four.

The outermost ports are common exhaust ports in that each services two cylinders. They also have two mounting holes each for a total of four.

It looks like this:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=220551869678

I've had another thought. When was the last time the valve clearances were checked? You could have a valve or valves hanging slightly open when the motor heats up. I know you have the manual. I see .010 for the intake and .019 for the exhaust, both when hot.