At the end of my rope!!!
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Freshman User
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At the end of my rope!!!
I have a 66 F100 300ci 1bl carter YF carb. It sputters at high speed when I push more than 1/2 inch down on the accelerator. At low speeds I can press over half way down before it starts sputtering. I have soaked the carburetor and rebuilt it, new air filter, new fuel filter, new fuel pump, new plug wires, new points (set @ .22), cap, rotor, vacuum advance, new plugs (gap set .32), coil, fuel lines, pcv valve, muffler and pipe, and thermostat. initial timing set at 8 and 38 on the vacuum advance. it advances at about 1500rpm. I've adjusted everything with a vacuum gauge and I'm getting about 17 constant vacuum. It does have a small intermittant quiver at idle. You can barely see the needle quiver. My compression is between 162-165 in all cylinders. I've noticed when I try to set my idle mixture screw with the vacuum gauge it doesn't do much. I finally just turned it in until the idle went down the back 1/2 turn. I've never adjusted the needle valve inside the carb. All I know is it bottoms out when the accelerator pump bottoms out. ????????????????? Any ideas? 
Cargo Master
Joined: Sep 2007
Posts: 2,095
Likes: 2
From: Wahpeton ND
Check your fuel pressure. First.
The YFA is a pain to get to work perfectly. The little linkage that attaches to the accelerator pump can be adjusted to give your squirt more duration. This is how that assembly works.
That diaphram recives vaccum on the bottom side pulling the needle and the diaphram down. The top side of the diaphram fills with fuel to act as an accelerator pump. As you push the gasyou lift that rod up overcoming the vaccum and squirting gas out and lifting the meetering rod out of the jet to supply more fuel. It also can act as a half arsed power valve. As you are driving and hit a hill vaccum will drop a bit. The vaccum on the bottom of that diaphram will ease up and force a dribble of fuel into the airstream to prevent lean stumble.
I dont have your carb in my hands, but my guess is you installed that little paper gasket on top of the accelerator pump. That will cause this problom. You can richen the overall mixture a bit by raising the rod in the well. You do this by tightening the screw to lift the rod. Though this will cause you to run richer at all throttle points.
Plan B- If this problom did not exsist untill you rebuilt the carb........Rebuild it again.
The YFA is a pain to get to work perfectly. The little linkage that attaches to the accelerator pump can be adjusted to give your squirt more duration. This is how that assembly works.
That diaphram recives vaccum on the bottom side pulling the needle and the diaphram down. The top side of the diaphram fills with fuel to act as an accelerator pump. As you push the gasyou lift that rod up overcoming the vaccum and squirting gas out and lifting the meetering rod out of the jet to supply more fuel. It also can act as a half arsed power valve. As you are driving and hit a hill vaccum will drop a bit. The vaccum on the bottom of that diaphram will ease up and force a dribble of fuel into the airstream to prevent lean stumble.
I dont have your carb in my hands, but my guess is you installed that little paper gasket on top of the accelerator pump. That will cause this problom. You can richen the overall mixture a bit by raising the rod in the well. You do this by tightening the screw to lift the rod. Though this will cause you to run richer at all throttle points.
Plan B- If this problom did not exsist untill you rebuilt the carb........Rebuild it again.
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you are absolutely right!!
I did install that gasket when I rebuilt it. You are saying that I should remove that gasket? Thanks for the carb info. I am brand new to carbs. This is the first one that I have ever tried to rebuild. I figured I should learn on a simple one. i'll try to get some time to take the gasket out tomorrow. I sure hope that's it.
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Freshman User
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I removed the gasket
It does run better, but it didn't solve the problem. It still stutters when I press the throttle down more than half way. It seems as though it is starving for fuel. When I pull out the choke about 1/4" it does WAY better. I noticed when I put the carb back together that at closed throttle position the needle is not bottomed out in the hole. Also the adjustment screw on the needle is no where close to touching the green arm. You could turn the screw in 1/16" before it would contact anything. The little spring on the side of the needle is keeping the needle from bottoming out in the hole. I can push on the top of the needle and it will bottom out, but then springs back up. If i press on the top of the needle and the accelerator pump they both will bottom out at the same time, but I have to literally push on the top of the needle to make that happen. Is this how it is supposed to work? Thanks for you help.
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Freshman User
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ok...
I tightened the screw at the top of the needle valve about 1-1/2 turns. It helped the problem a lot. My spark plugs are showing me that I am still running a little lean. they are white on the end of the tips. My idle mixture screw is turned out about 2-1/2 turns. Since I've tightened the screw on the top of the needle I can push the accelerator about 3/4 down before it starts sputtering. should I keep going until the sputtering stops? The needle no longer bottoms out with the accelerator pump. It hits the screw first. Am I on the right track? It really sucks that you have to take the carb apart everytime you adjust the screw.
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Cargo Master
Joined: Sep 2007
Posts: 2,095
Likes: 2
From: Wahpeton ND
Gotta love the YFA. If you can drive it around normaly once the engine is warmed up, I would leave the mixture setting alone. Your plug coloring is sounding about right. The driveability is the main factor here. Try driving it.
I am glad pulling that gasket helped. I had to learn that one the hard way.
I am glad pulling that gasket helped. I had to learn that one the hard way.
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