That the engine will idle well is a good indication of a mechanically healthy engine.
Typically, requiring full choke to run is an indication of a lean fuel issue.
But it can also be weak spark. So before opening the fuel system and having gas leaking out, check the points, check the gap, check the distributor shaft for side play (it must be tight for the points to stay set). Finally, start it up, pull one plug wire at a time from each plug, (pull the boot back to expose the metal end first), then pull the wire off the plug, holding it near something metal, it should arc a thick, blue hot spark at least 1/4 inch.
If that checks good, move on to the fuel system. There is a plug in the bottom of the carb. Get a clean glass, with the engine off, fuel valve open, remove the plug, catch the flow in the glass. (If there is a fuel pump, run the engine at idle) There should be a steady stream of fuel, not slowing to a drip or stopping. Look at what is caught. Should be clean, clear gas. No water (cloudy ethanol gas means water), rust, dirt... Any contamination means the carb is also contaminated. A dirty tank will need to be removed and cleaned, a rust flaking tank will be an ongoing problem. Consider replacing it, save yourself a lot of frustration!
If the flow test fails, start checking back toward the tank. Find where the obstruction is. There should be a screen in the carb inlet elbow, be sure to check it.
Once flow through the carb is established, replace the plug, move to the next step.
If it has been sitting a couple years, even if it was run out of fuel, there may still have been enough gas left in the carb to have clogged the jets.
But before assuming so, do another test. If there is a main jet adjustment screw (a larger adjustment screw on the bottom of the carb, or through the top, angled down toward the bowl), try gently turning it in until it just stops, then back it out about 2 to 3 turns.
Start the engine, see if that changed anything. If yes, move on to the main jet adjustment. If no, time to go into the carb.
These carbs are very simple and field serviceable. Don't be afraid of it. Look for a name brand and a tag number if you can find one. There is a lot of information online and on Youtube explaining how to open one up and clean it. Usually, it can be eased apart, cleaned, and reassembled without having to buy a kit or gaskets.
If you go into it, be sure to work over a clean surface. Short nap carpet works well. Loosing something is the biggest risk. Have some spray carb cleaner ready, and compressed air if you have a compressor. Clean, poke, and blow through every passage. Having a flow diagram (available online) will help understand how it works, how fuel gets from the bowl, through the jets, and delivered to the engine. The main jet will need to be scraped out with a wire or tiny drill bit. Clean it thoroughly but try not to enlarge it. Spraying, blowing, and looking through it will not get it clean, it needs to be scraped out.
Set the float level by the specs, important setting, don't guess.
Once back together, set the adjustments.
With the engine up to operating temperature, oil clean and at the proper level, air cleaner serviced and free of obstructions (mud dobber and mouse nests), ignition tuned, valve lash set, everything up and running, ready to go...
Start with the idle adjustment. The engine must be idled down to the 400-500 RPM range, any faster the idle adjustment will have on effect. Turning the idle mixture screw in richens the mix, out leans it. Just opposite a typical down draft, you are adjusting air bleed, not fuel flow. Adjust it for the best idle.
Then set the main jet (if adjustable). Start about 2 turns off the seat. With the engine idling, suddenly open the throttle. If the engine stumbles, open the adjustment (turn it out) 1/4 turn. If the engine did not stumble, turn it in 1/4 turn. Keep repeating the test, adjusting the jet, until the engine will take sudden, full throttle from idle without stumbling. A single puff of black smoke is normal and desirable.
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Today's Featured Article - Listening to Your Tractor - by Curtis Von Fange. Years ago there was a TV show about a talking car. Unless you are from another planet, physically or otherwise, I don’t think our internal combustion buddies will talk and tell us their problems. But, on the other hand, there is a secret language that our mechanical companions readily do speak. It is an interesting form of communication that involves all the senses of the listener. In this series we are going to investigate and learn the basic rudimentary skills of understanding this lingo.
... [Read Article]
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