Re: ford 641 Idle speed

Posted by Steve@Advance on January 03, 2019 at 05:40:17 from (24.182.105.179):

In Reply to: ford 641 Idle speed posted by bobrobert58 on January 02, 2019 at 21:50:45:

Welcome bobrobert58!

Hopefully we can help get this running properly.

How is the rest of the engine? Any vacuum leaks, compression problems, excess blow-by, valve lash set? Have you ran a compression test? Plugs, wires, points, distributor shaft wear, timing, centrifugal advance working?

If the engine is not healthy, or properly tuned, idle quality will be less than satisfactory. Be sure everything else is as it should be before pursuing carb problems.

As for the carb, how clean is the fuel? If the tank is contaminated with rust, sediment, water, the same will be in the carb. You can take a sample from the drain on the bottom of the carb. Catch some fuel in a clean glass, see what you catch. If contaminated, the tank will need to be cleaned or replaced, depending on how rusty it is. Sometimes cleaning will cause leaks, so be prepared for the worst unless the tank has already been replaced.

Also, how is the air cleaner? Has it been disassembled and the mesh cleaned? That is often overlooked. It periodically needs to be washed out or even replaced in severe cases. Also check for other obstructions in the pipe, mud dobbers, mouse nests, etc.

Once clean fuel is available to the carb, (and you may need to clean the carb again if the fuel was dirty), and everything else is good, or as good as you can get it for now, proceed with adjusting the carb. Don't be afraid of opening up the carb. They are simple and field serviceable. Lots of online info on them, pictures, theories, etc. Just work over a clean surface so not to loose anything.

You say it is prone to flooding. A true flooding updraft will drip gas anytime the fuel valve is open and the engine not running. A float that is partially sunk, float level out of adjustment, bent float hitting the side of the bowl, damaged or loose needle/seat, or (most commonly) trash in the needle/seat, will cause flooding. If any of those conditions are present, they will need to be repaired first. Clean fuel is essential. I like to flush the line as the last thing before making the fuel line connection. Turn the fuel on before making the connection, that way any trash that may have been in the line will flush out before screwing the line to the carb.

A few drops of fuel out the air horn following a failed choke assisted start is normal for an updraft and does not indicate flooding.

To adjust the idle mixture, the engine needs to be up to operating temperature (thermostat working?). The engine must also be idled down to the 400-500 RPM range. Anything above that and it is off the idle circuit. Turning the idle mixture adjustment screw (the small screw up by the mount flange) out leans the mixture. Turning it in enriches the mix. You are actually adjusting air bleed, not fuel, therefore it adjusts backward from more modern carbs. If the adjustment screw makes no difference, either the idle circuit is clogged, or the idle speed is too high and it is running off the intermediate circuit. That is why it must be idling slow enough to be on the idle circuit to adjust it properly.

To adjust, turn the screw out until the engine falters, then back in to good idle, then in slightly to rich, but not poor idle.

The high speed mix, (the larger adjustment screw), adjusts the fuel flow through the main jet. Turning it in leans the mix, out enriches it. With the engine at idle, turn the screw in a turn or so, quickly open the throttle. It should hesitate or die. If not, keep turning the screw in until it does. Then start backing the screw out 1/4 turn at a time, repeating the test with each adjustment. Once the engine will respond to sudden full throttle without hesitation, the high speed is set. A single puff of black smoke is desirable.

Hope this helps, let us know...

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