IH 340 won't run when it's hot except with choke on

Tom hater · Apr 27, 2009

I have worked as a mechanic for many years, but this one has me stuck I have a IH 340 utility, with only 2,000 hours on it. It runs perfect until it gets to operating range with all the power you want, then it will only run when choked, first just a little choke, then the the choke must be fully pulled out. I have taken the carb apart at least a dozen times, and none of the air passages are cloged. The tank is also clean, and full fuel goes to the carb, and out of the drain. the floats are set properly. I have also replaced every electrical component on the tractor. Does anyone have any suggestions?

Mark W. · Apr 27, 2009

Might be a shot in the dark but is your choke hooked up backwards maybe?

old · Apr 27, 2009

Does the fuel line run any place that it gets hot?? If it does the gas maybe boiling in the line and that will cause that type of problem. Could also be a coil going bad and causing a weak spark when hot
Hobby farm

Andy Martin · Apr 27, 2009

Have you checked to make sure the fuel cap is vented?

Hook a plastic U-tube up to the carburetor drain so you can monitor the fuel level in the carburetor while it is acting up.

I had a C once which had a ring of fuzzy debris (I accused my help of using a stick to check gas level) which would float around in the gas tank causing no problem until it decided to get sucked around the fuel outlet and just about kill the tractor. Then with no load it would float away and the tractor would run great, for a while. We only found it after draining the tank through the carburetor. We missed it turning the tank upside down twice. It may have been gasket material.

Bob Kerr · Apr 27, 2009

Check for a loose manifold.

Bob M · Apr 27, 2009

That's my thought too. Sounds like an intake manifold leak opening up as the engine heats up.

Tom hater · Apr 27, 2009

I sprayed both water and starting fluid around the manifold and carb while rumming, no change. It apparently is not picking up any outside vacuum. The manifold pulls 20lbs of vacuum at the intake plug.

Tom hater · Apr 27, 2009

It runs the same with or without the fuel cap. I have a sight glass that came out of an oll set of carb tools that I screw on to the carb, the fuel level in the carb remains constant.

Tom hater · Apr 27, 2009

I put a new coil, points, condenser, wires,cap, rotor, plugs, and everything else electrical on it, also I have used a temporary mounted fuel to test for vapor lock, or some other related problem with no change.

Tom hater · Apr 27, 2009

The choke is correct, you have to choke to start it, unless it is warm out, then as is normal procedure you can push it in after it starts.

Anonymous-0 · Apr 27, 2009

Have you checked spark quality when the tractor is hot? Is it 6 or 12 volt? If 12 volt, are you using a 6 volt coil with a resistor or a 12 volt coil without a resistor? If 6 volt, you must use a 6 volt coil without a resistor. Have you tried a known good condensor? Have you checked valve lash? Why do you hate Tom?

Janicholson · Apr 27, 2009

The intake manifold may be cracked internally and when hot (from exhaust manifold contact) allows an internal crack to open to exhaust.
AND
Only check for intake leaks when the engine is hot enough to force the use of the choke. Use propane from a torch with the air mixing tip taken off. (outside) JimN

Tom hater · Apr 27, 2009

I have done almost the same thing, I have sprayed starting fluid all around the manifold while it was hot and running, if it had a leak, it would rev up. also a vacuum gauge on the manifold shows 20 inches of vacuum

Tom hater · Apr 27, 2009

I have a 12 volt system, with resistor, condenser has been changed. The tractor has been in the family for about 40 years and it has always run great, until it just started getting progressively worse, it only has 2,000 hours on it. I thought about checking valve lash, but since the engine pulls 20 inches of vacuum at idle, that is usually a sure sign that valve timing is good.

Janicholson · Apr 27, 2009

20 is not terribly exciting, But a crack internal can't be checked from outside. JimN

bc · Apr 27, 2009

Another shot in the dark here, but is there a gasket leak between the intake and exhaust manifold or maybe the butterfly between the exhaust and intake sticking?

mattofvinings · Apr 27, 2009

This sounds a little like a problem I had a few weeks ago. Some sort of trash got sucked from the fuel tank and restricted the flow.

Suddenly the tractor would only run with full choke and then die off.

It was obvious that a few drips weren't enough once the sediment bowl was removed and that's all that was flowing out.

I blew back thru the fuel line to clear the blockage and get running again...but the problem isn't forever resolved unless I undertake some more thorough fuel tank cleaning.

806 Curt · Apr 27, 2009

Sounds like an interesting problem you have there... So is it actually running lean that she wont stay running? Or does she only run with a rich mixture when warmed up? To keep it running with the choke out is it blowing any black smoke? If its blowing black and thats the only way she stays running, then most likely you have an ignition problem. If it runs normal (not rich) with the choke out then its simply got to be starved of fuel in the carb somehow. Interesting coincidence that it only does it when hot... Is this at a light load? full load? no load? All I can think of is if the fuel is vaporizing somehow in the fuel line... I dont know, interesting problem you have there, let us know what you find.

MN Mike · Apr 28, 2009

I'm having similar trouble with my 340 but [I think] I have it tracked down to an old set of points. The sparak was pretty weak and the points were worn down and pitted. Should have it back together later this week so I'll know if that did it or not.

Tom hater · Apr 28, 2009

I just put a new set of points in and they are set properly

Tom hater · Apr 28, 2009

It will start and run normal and the closer it gets to operating range, the more I have to choke it. It does not blow any black smoke ever. If I continue to run it even after it gets hot with the choke engaged fully, it will eventually die completely, I will have to let it cool to restart. I have even used an auxiliary fuel tank mounted away from any heat source, and the problem still occurs. The problem occurs at no load or full load, no difference.

Tom hater · Apr 28, 2009

The fuel line as it runs into the carb will a quart can with fuel in about 30 seconds, with only slightly slower results as it runs out of the carb drain plug.

Tom hater · Apr 28, 2009

Checked those.

Tom hater · Apr 28, 2009

That is not what I what to hear, but perhaps as a last resort I will have to pull the manifold.

Tom hater · Apr 28, 2009

I would think that there was a crack in the manifold, the engine vacuum would drop drastically, it remains constant around 20" of vacuum.

Anonymous-0 · Apr 28, 2009

What is the quality of spark when the tractor dies? Your tractor came from the factory with a 6 volt system. It now has a hybrid 12 volt system. Are you using a "true" 12 volt coil or a 6 volt coil with a resistor? If you are using a 6 volt coil, then the resistor must be matched to the primary resistance of the coil. Just any resistor won't do. Does your system use a resistor bypass for starting? These can be misleading as you will have good spark while the resistor is being bypassed during cranking, but weak spark on run.

If this checks out ok, it is probably time to take the manifold off. With the manifold off, I usually fill the exhaust side with water and see if it seeps into the intake side. No pun intended, but I would exhaust all ignition possibilities before tackling the manifold. Let us know what fixes it.

RedJohn-2 · Apr 28, 2009

tom hater, I had the same problem with a IH 300. Suggestion: check voltage exiting resister to coil. (In my case the voltage drop was only to 9.9 volts. I installed 2 resisters in series; then the voltage dropped to 4.9 volts. The tractor has been running perfect for a year now).
Good luck. John

steelfronts · Apr 29, 2009

Tom I had a W30 that did the same thing exactly. Intake manifold had a crack the expanded as soon as it started getting hot. Tractor always started right up acted like it was ready to go but by the time it did 100 feet on the plow the choke had to be pulled to keep it going.

IH 340 won't run when it's hot except with choke on

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