Carburetor Theory
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From: Virginia Beach, VA
Carburetor Theory
My 78 super cab wont start. It will run on carb cleaner but not on fuel through the carb. I just had the carb rebuilt. I'm thinking the if the float is down then it brings in fuel, and when the float is up it shuts off fuel to the bowl?
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
It works just like a toilet, but instead of a flapper, there is a needle and seat. The float works by leverage action. As fuel level goes DOWN, the float drops, the needle rises, and fuel is allowed in. As fuel level goes UP, the float rises, the needle drops, and fuel flow is shut off. This back-and-forth action regulates the fuel level in the bowl.
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
If the bowl is empty such that the float is completely dropped, yet the needle is seated, then the float height is severely out of adjustment. Setting the float height is standard practice when rebuilding a carburetor. If someone returned the carburetor to you in this condition, they did not know what they were doing.
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Cargo Master
Joined: Apr 2009
Posts: 3,038
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From: South west Idaho
The best way to adjust it is take it back to the rebuilder if it was this way when you received it. If you open it up , mess around with it and still have problems getting it right , the rebuilder may and can refuse to fix it for you with out extra charges. If it started out okay but then gave trouble then you may have crap in the fuel that is lodging in there. Do you have a fuel filter in the line ? A lot of carb problems start with contaminated fuel.
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MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
Float height is adjusted by bending the tang of the float to control how high the float is supposed to rise before it seats the needle. A "dry" adjustment is made during the rebuild by measuring the end of the float relative to the top of the bowl with the needle seated. A wet measurement is made with the engine running by measuring the level of the fuel relative to the top of the bowl (much more involved). I agree with Jim though. Assuming you paid someone to do this, have them fix it, or at least refund your money since they obviously don't know what's going on.
Are you sure this is what's happening though? You have to really try to set things up the way you're describing. You're saying the float is all the way down and the needle is still seated? That means you wouldn't be able to push the float up at all. You'd have to bend the tang pretty far to lock it up like that. This means there would be absolutely no fuel in the bowl either; is that the case?
Are you sure this is what's happening though? You have to really try to set things up the way you're describing. You're saying the float is all the way down and the needle is still seated? That means you wouldn't be able to push the float up at all. You'd have to bend the tang pretty far to lock it up like that. This means there would be absolutely no fuel in the bowl either; is that the case?
Cargo Master
Joined: Aug 2007
Posts: 2,561
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From: New Zealand
I had the same situation recently with a 2150.
The needle & seat supplied in the carb kit (match for carb tag#) were about an 1/8" too tall, so the float sat low & had very little travel.
To bend the float tab enough to get the correct fuel level, would have messed up the angle that it operated the needle at.......so that needle/seat assembly wasn't usable.
The needle & seat supplied in the carb kit (match for carb tag#) were about an 1/8" too tall, so the float sat low & had very little travel.
To bend the float tab enough to get the correct fuel level, would have messed up the angle that it operated the needle at.......so that needle/seat assembly wasn't usable.
Elder User
Joined: Feb 2011
Posts: 575
Likes: 6
From: Knoxville, TN
I had the same situation recently with a 2150.
The needle & seat supplied in the carb kit (match for carb tag#) were about an 1/8" too tall, so the float sat low & had very little travel.
To bend the float tab enough to get the correct fuel level, would have messed up the angle that it operated the needle at too much.......so that needle/seat assembly wasn't usable.
The needle & seat supplied in the carb kit (match for carb tag#) were about an 1/8" too tall, so the float sat low & had very little travel.
To bend the float tab enough to get the correct fuel level, would have messed up the angle that it operated the needle at too much.......so that needle/seat assembly wasn't usable.
That's my thought. Wrong size needle for the float or vise versa or both are wrong.
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