Money well spent ....But

Gchase24 · Oct 18, 2017

Bought a new carb for my little 68 IH cub.I hadrebuilt the old one several times ,could not get it to run to my satisfaction.Fluttering or running rich ,fouling plugs.Bought the new one from a IH dealer. It is a IH ,not a china knockoff. IT runs ,starts great.Plenty of power(for a cub).The only issue is if you throttle back slowly it will idle fine .But if you throttle back all at once it will die out. New plugs,Timing,points,rpm @ idle set to specs from service manual.Governor rod adjusted according to manual.Thought maybe intake was clogged so I cleaned the air tube/wire mesh in cleaner . Did not help. Any ideas?

roy prins · Oct 18, 2017

when it is at full throttle the intake is full of gas -- when you bring it back real quick to the idle position there is to much fuel in the intake for the engine to idle properly -- Just My thoughts on it -- take it for what its worth -- Roy

47fivewindow · Oct 19, 2017

Try increasing the idle speed a little.

Hobo,NC · Oct 19, 2017

Check Valve adjustment. I don't know how on a cub the OHV engines will experience the issues you have if they are too tight...

Traditional Farmer · Oct 19, 2017

A lot of older tractors will shut down if throttled back quickly especially if the idle is set to a real low RPM.Why would you throttle back to idle real quick anyway?

Gchase24 · Oct 19, 2017

Thanks for all the responses.I have tried to increase the idle speed some but then it will idle too fast.The problem did not show up until the new carb was installed.Five years since the overhaul so I don,t think the valves are too tight but I probably do need to check the clearance. With the old carb it would idle slow enough that you could almost count each time it fired.Not being disrespectfull I don't need to cut the throttle suddenly.Just a normal idle back like I've done for years it will die.

showcrop · Oct 19, 2017

(quoted from post at 19:46:15 10/18/17) when it is at full throttle the intake is full of gas -- when you bring it back real quick to the idle position there is to much fuel in the intake for the engine to idle properly -- Just My thoughts on it -- take it for what its worth -- Roy

At full throttle the intake is full of AIR not gas. Higher velocity air flow through the Venturi draws more gas to mix with the fuel. I would be checking the float level.

Indiana Ken · Oct 19, 2017

A loose fit between the throttle shaft and the carburetor body can cause a sub-idle condition. However, that is typically due to wear and you have a new carburetor.....right? You can check for looseness by attempting to wiggle the throttle shaft with your fingers.

Also, with the engine idling normal, try pushing the throttle shaft hard (finger pressure) against the stop screw. If the idle speed changes you could be idling on the governor, adjust the linkage to put the throttle shaft hard against the stop screw.

Money well spent ....But

Gchase24

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roy prins

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47fivewindow

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Hobo,NC

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Traditional Farmer

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Gchase24

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showcrop

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Indiana Ken

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