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kbailey: That's one of those Marvel-Schebler carburetors with the electrical solenoid, right? Even without the solenoid, it's still the decades old M-S updraft design, and when they surge, it's most often a "lean on idle" condition caused by a vacuum leak at the carburetor flange gasket or a plugged idle circuit. Rule out the gasket by tightening the mounting bolts, and then spraying some flammable liquid around that seam. If the engine picks up speed or the loping improves, you might have found at least part of the problem. The cause that has the highest probability of being the fault is that of the clogged idle circuit. What happens is that while trying to idle, the carburetor gets short of fuel (lean) in the idle circuit because either the needle is open too far (idle needle meters air, not fuel, right, so "in" gives more fuel...been a awhile for me), or the circuit is clogged or otherwise restricted. Since the engine cannot maintain its speed at that chintzy amount of fuel being metered, the rpm's begin to fall. As soon as this happens, the governor cannot maintain equilibrium with the spring pressure of the throttle, the throttle spring wins, so the carburetor butterfly opens, and the carburetor gasps for air and fuel from wherever it can get it. If the idle circuit is restricted or flat plugged, the fuel will come from the load circuit (which is functioning fine since you said the engine runs all right under load conditions), the speed will pick up (rapidly!), the governor will close the throttle plate to the normal "idle" position, and the process repeats itself. Again, again, and again. So, try to feather in just a little choke to compensate for the missing fuel in the idle circuit. If you can manually correct the loping using the choke, you've proven for the most part that the idle problem cause is a clogged/restricted idle circuit, and you'll probably have to go into the carburetor and run a soft wire through the idle passages (of course you'll run them all), blow them out, and perform all the adjustments. If this is not the case, then you might have to look into the throttle/governor linkage adjustment, but I'm betting that you correct the loping when you clean out the idle passages. If you do go to the governor adjustments, check the timing to ensure that the engine has every chance of idling correctly before you begin those adjustments. You'll pin it down and fix it. Frank
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