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I was recently talking with my auto shop teacher from high school about my M37. He was my teacher almost 30 years ago. When I told him the truck has no vacuum advance, he recommended I set my timing for 8-10 degrees before TDC. I am currently set at 5 degrees before TDC and the truck is running well at 8000' elevation. I recently had the carb and distributor redone at M-series rebuild and it is running great. The one thing that seems different though is that I no longer need do use the choke to start the truck. I think I might be running a bit rich. Would I need a special main needle for this altitude? I could use any advice on timing and carb adjustment anyone could give me. My only carb adjustment experience is on 2 stroke dirtbikes.

The extra degrees advance are for the modern fuels. If you are not having to use the choke to start that means that your idle mixture has become more rich. It would be best to gage main metering mixture from your spark plugs not how she starts.

Thanks Cuz. I'll start with the idle screw.

You can also use a vacuum gauge to help. In the aircraft business we call them a manifold pressure gauge and all piston engine aircraft with constant speed props have them on board permanent. Many light aircraft without constant speed props also use them for monitoring engine power. Gauges used for troubleshooting and adjustments are handy to have aboard all the time. Some folks just install an under dash set of gauges which often include the vacuum gauge, volt meter and RPM. You can even hide these in the glove box and they will be there always ready to help you out.