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I had a number of IH vehicles of that era, and used them in a snowplowing business. But I did not have any Scouts, nor any 6 cylinder Rambler engines. So I'll just take a few guesses based on mechanical experience from that time period. I would look carefully at the choke plate in the carb. When you are moving slowly, like plowing, does the choke plate close? The chokes of that time used a combination of methods to control them. They usually had a vacuum line that would allow the choke to close when the vacuum is low, so as to enrich the mixture to allow cold drivability. I remember that there were different places that these carbs would pull vacuum from. One place was the venturi area, another was the intake manifold area just below the carb bottom. I don't know which carb you have and which vacuum connection should be made. The choke plate was opened by a bimetal spiral spring that would expand when it got hot. Some of these used a steel vacuum line (about the size of steel brake line, but short) to go to a little sheet metal "stove" on the exhaust manifold. It would pull hot air into the spring area and the choke would open. The next newer method of choke control was the use of an electric heating coil close up to the bimetal spring. So as the vehicle ran the electrically created heat would open the choke. But if the Scout runs OK at normal driving speed, I think the choke heater system is working OK. Normal driving speed and high idle speed will create high vacuum and the choke plate should remain full open. Low speed and lugging to pull or push means low vacuum and the choke plate may be closing giving too rich a mixture on a warm engine. Another possibility is the vacuum advance on the distributor. Some were to be hooked up to venturi vacuum, and the others were to be hooked up to the intake manifold. If this is incorrect, your dist may be giving you a retarded timing condition at low speed and thus low vacuum and that can lead to plug fouling and poor power. First, I would follow up on the other respondents suggestions, as they are good, but if their suggestions do not solve the problem, I would try to find out how the choke is acting and confirm the correct place that the vacuum advance draws from. While you are there, confirm that a vacuum created by your mouth (sucking) will in fact move the distributor advance plate (where the points are screwed to). Good luck! Paul in MN
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