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I have a 23 hp kohler that runs fine for a short time,then starts to rev up and down.If i put it on half choke,it sounds good again,,,I have put a new fuel filter on,new plugs,and a brand new carb.
I checked the fuel pump also,,puts out good
It is on a Derby zt2354,,,,,,,any ideas would be greatly appreciated

The one clue we have is response to choke. Is the engine up to temperature when it responds to choke? Despite "new" carb perhaps you should check the float level and inlet needle and seat. Next possible gas line / fuel filter blockage. Take compression if you have a gauge , etc.

motoman said:

The one clue we have is response to choke. Is the engine up to temperature when it responds to choke? Despite "new" carb perhaps you should check the float level and inlet needle and seat. Next possible gas line / fuel filter blockage. Take compression if you have a gauge , etc.

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There are a few times it'll run good without choking it,,very seldom though,,it needs half choke when cold or hot.
Fuel comes out good at the pump outlet,,i took the hose off and cranked it,good pressure.
its got 155 and 165lbs compression
I've taken the old carb off twice and cleaned it,,not much fun,l was hoping I didn't have to do it again,lol

I am wondering when the engine warms up you are getting some heat related warpage of the intake manifold causing an air leak.

alan, Sounds to me that the engine is not receiving enough fuel in the airstream to product power and stay running. When you half choke you are crutching the carb by making the choke fuel inlet produce the missing fuel. And it seems this may rule out a float problem as (I think ) both the choke and main fuel jets depend upon the same fuel puddle in the float chamber. So perhaps carefully probe the main jet with soft copper wire and solvent if you can identify it. Since I do not have 1st hand knowledge of the particular carb it may be possible to remove the jet and then access small passageways. Usually when I rave on like this someone takes mercy on you and gives you a real fix. Keep being patient.

ILENGINE said:

I am wondering when the engine warms up you are getting some heat related warpage of the intake manifold causing an air leak.

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It does when cold also,,but I'm considering all options,,just hope its not that one,lol

Sorry for the late response,,,i finally broke down and took the brand new carb off,,and,low and behold,while I blew thru the intake line while raising the float,i could hear air still escaping.
So,i cleaned the float valve,put carb back on,,so far,so good,,
Thanks for all the advice