Poor Running 340 Utility When Warm

Michigan IH · Jan 3, 2010

My gas 340 utility runs fine when first started, but after 20 or 30 minutes (especially if idling) it starts to run like the choke is out. It stumbles and sputters when you give it gas, it does the same when it encounters a load. Sometimes it will back fire through the exhaust. It has 1900 hours on the meter. I installed a new crank at 1400 hours but have not had the head off. This condition occurs in cold or warm weather. In addition to the poor running, the carb is also wet on the outside all the time and moisture comes down the block from the manifold runners. I tried a heat houser last winter with no impact.
Any ideas??

ih560 · Jan 3, 2010

Sounds like you might need to readjust the carb once the engine is warm. Engines typically need to run a little rich when cold, hence the need for a choke. So if you adjust the carb to run well when cold, then it is going to be rich when the engine is warm.

old · Jan 3, 2010

Sounds like it is running a little on the lean side and you need to open up the main jet a little bit. 2 ways you can do it and both ways work. #1 open it up till you get black smoke then turn it in till the smoke stops or #2 open it up and try it and keep doing that till you have good power and no smoke

jesse007 · Jan 3, 2010

Hello sir,
As you are probably well aware a U or F 340 is normally a smooth sweet running machine with adequate power and good fuel economy.
Here are the items I would check if it were my 340:the carburetor float level and action to make sure it isn"t sticking so the float can regulate the fuel level properly,check for partially plugged jets,try another set of spark plugs especially an old set if you knew they worked properly-I have had some hideous experiences with new but defective plugs that had symptoms a lot like you are experiencing,you might try another condenser or coil if all else fails-if you give me your phone number and a convenient time to call I"ll try to help you that way
take care and good luck!

MN Mike · Jan 4, 2010

the only thing I'll add to the great suggestions is to check your condensor and points. I replaced a pitted set of points on my 340 last spring and found a motor that ran a lot better under load.

Rumplestiltskin · Jan 4, 2010

Assuming a battery ignition, you may want to try a different coil. Sometimes they function well until they get warm, then....

Mark W. in MI

Cub149 · Jan 4, 2010

If not the coil, could the valve adjustment be too tight? When the valve gets hot and expands, it is held off the seat causing power loss and popping.

Poor Running 340 Utility When Warm

Michigan IH

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ih560

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old

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jesse007

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MN Mike

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Rumplestiltskin

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Cub149

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