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Farmall & IHC Tractors Discussion Forum
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300 carb adjustment question

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Zak

03-25-2004 18:06:47




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So I've just finished rebuilding my 300's engine with new pistons and the works. I also rebuilt the carb in the process. After discovering that I had the distributor off by 180 degrees (duh!), I'm still not getting any fire! I've checked the spark (good), I have oil pressure, plenty of compression, and the valves are spot on. My carb has two adjustemtn screws. One right near the carb manifold flange and one down lower. Which is idle and which is main? How many turns out on each is a good "start" point? So far all I've managed is a mighty impressive backfire out of the carb (see distributor) but nothing in the cylinders. I'll assume I've got a fuel issue at this point. Thanks all. Zak

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Will Sick

03-26-2004 09:34:53




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 Re: 300 carb adjustment question in reply to Zak, 03-25-2004 18:06:47  
Make sure you haven't gone the wrong way on the firing order when putting the plug wires in the distributor cap.



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rebuilder

03-26-2004 03:36:33




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 Re: 300 carb adjustment question in reply to Zak, 03-25-2004 18:06:47  
Zak;

All the farmall carbs I rebuild use the following adjustments;
1)Needle at the bottom of the bowl is the fuel adjuster to the main jet; Turn three revolutions out from snug seat.

2)Top needle is the idle adjustment turned 1 and 1/4 revolutions out from snug seat.

3)Throttle stop screw to 1 and 1/2 turns to open throttle plate from completely closed position.

These basic adjustments should get you close.

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Zak

03-26-2004 07:24:48




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 Re: Re: 300 carb adjustment question in reply to rebuilder, 03-26-2004 03:36:33  
Ok, I've got the Idle and the throttle stop adjusted, but my main jet does not appear to have the adjustment screw? I have an older 300 carb that does have the adjustment screw on the bottom. The carb that is on the tractor, has a flat where the adjustment screw is located on the other carb, but there is no provision for actually having a screw (if that makes sense!) In other words, I don't appear to be able to adjust the main jet from the outside of the carb as there is no visible screw to adjust! Is it internal on this carb (which I assume is original to the 300, just a later model maybe?)

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rebuilder

03-26-2004 12:35:58




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 Re: Re: Re: 300 carb adjustment question in reply to Zak, 03-26-2004 07:24:48  
Zak;

Your carb should have the hole for the main needle. I have only seen one or two carbs with that area left blank(not bored or threaded) and still have no idea what application it would serve. All the farmall carbs from the H's-560's used the main needle and I even sell quite a few kits to put the needle into the bigger carbs up to the 856(c-301). This lets people remove the fuel shut-off solenoid which is put in the same place instead of the main needle. So you need to contact your favorite salvage yard and get either the bowl or the complete carb with the main needle, the packing, and the packing nut(brass).
Carb number should be 361525r91 founnd on tag on throttle body.

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CNKS

03-26-2004 18:18:36




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 Re: Re: Re: Re: 300 carb adjustment question in reply to rebuilder, 03-26-2004 12:35:58  
The Super H, and I assume the 300/350 - I only have a Super H, has the main screw turned 5 turns out for maximum power. The operator's manual says the screw can be turned in for better fuel economy if max power is not needed. I take this to mean a "fixed" jet that is adjustable. I bet I could put a plug in place of the adjusting needle on my Super H, and see no effect -- thus the blanks on some carbs. Personally, I don't like one I can't adjust.

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Ken in Iowa

03-25-2004 19:54:50




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 Re: 300 carb adjustment question in reply to Zak, 03-25-2004 18:06:47  
Zak: Remove a couple spark plugs and prime the cylinders with about a teaspoon of fuel, then reinstall the plugs and see if it fires. This test should tell you if it will run. If it backfires, double check your timing and firing order. Ken



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