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Old 02-09-2013, 02:39 PM   #1 (permalink)
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Default 4100 rebuild questions

I purchased a 1.08 4100 carb a few years back. Information stamped on the lower foot of the carb is 6A AC. The primary jets are 48 and secondary jets are 58. It appears to have originally had a hot idle compensator. Is this a necessary piece to replace to make the carb work correctly? The screws that once held it in place were broke off at some point and would need to be drilled out.

The rest of the carb cleaned up nice, not as nice as the painted ones on ebay, but clean and nothing frozen up.

I was hoping to clean it up, put a kit in it and have it ready to install on my 289 when ready. My plans for the engine are to keep it primarily stock with the exception of maybe an RV cam like the edelbrock performer plus and lightly porting the heads to match the exhaust manifolds.

Will this carb work or should I look for another?
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Old 02-09-2013, 03:28 PM   #2 (permalink)
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Originally Posted by jstang65 View Post
I purchased a 1.08 4100 carb a few years back. Information stamped on the lower foot of the carb is 6A AC. The primary jets are 48 and secondary jets are 58. It appears to have originally had a hot idle compensator. Is this a necessary piece to replace to make the carb work correctly? The screws that once held it in place were broke off at some point and would need to be drilled out.

The rest of the carb cleaned up nice, not as nice as the painted ones on ebay, but clean and nothing frozen up.

I was hoping to clean it up, put a kit in it and have it ready to install on my 289 when ready. My plans for the engine are to keep it primarily stock with the exception of maybe an RV cam like the edelbrock performer plus and lightly porting the heads to match the exhaust manifolds.

Will this carb work or should I look for another?
the hot idle compensator was used only on auto trans cars. it has no function on the operation of the carb. it helps to slow the idle down to prevent stalling.
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Old 02-09-2013, 03:49 PM   #3 (permalink)
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The 1.08, with the mods you are contemplating, is perfect. Going to a 1.12 will reduce the throttle response. I oughta know - went down that path myself. My engine is a 331, Boss 302 cam, ported with larger valves. Stock intake and a 1.08 with 58 primary, 67 secondary. Never pulled more than 430cfm on the dyno, within the range of the 1.08. Good luck!
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Old 02-09-2013, 04:57 PM   #4 (permalink)
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the hot idle compensator was used only on auto trans cars. it has no function on the operation of the carb. it helps to slow the idle down to prevent stalling.
Ah, no, that would be a dashpot. The hot idle compensator was a bimetallic spring that opened a vent to manifold vacuum. When the valve senses air coming into the carb is too hot, maning it might be overheating, the valve opens, reducing manifold vacuum, which increases idle speed, which cools the engine. Hopefully. A more accurate and reliable system was the Distributor Vacuum Control Valve, which first appeared on a few cars in 67, and by 68 Ford was using it on practically everything.

Many, perhaps all, 352 and 390 carbs had the hot idle compensator, but they were rarely if ever seen on the 289, except spliced into the PCV hose on AC-equipped cars.

Dashpot-



Hot idle compensator-

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Old 02-09-2013, 05:27 PM   #5 (permalink)
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Yes 22gt that is what I was talking about. Now since it appears one was originally on the carb I purchased and has been removed - broken off at some point will it affect how a 289 runs if not replaced?
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Old 02-09-2013, 05:29 PM   #6 (permalink)
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Yes 22gt that is what I was talking about. Now since it appears one was originally on the carb I purchased and has been removed - broken off at some point will it affect how a 289 runs if not replaced?
It'll give you a significant vacuum leak. I would plug the passage with a lead shot.
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Old 02-09-2013, 05:47 PM   #7 (permalink)
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It'll give you a significant vacuum leak. I would plug the passage with a lead shot.
Ok thanks. It appears to be plugged already.
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Old 02-09-2013, 05:56 PM   #8 (permalink)
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Yep.
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Old 02-09-2013, 06:42 PM   #9 (permalink)
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Originally Posted by 22GT View Post
Ah, no, that would be a dashpot. The hot idle compensator was a bimetallic spring that opened a vent to manifold vacuum. When the valve senses air coming into the carb is too hot, maning it might be overheating, the valve opens, reducing manifold vacuum, which increases idle speed, which cools the engine. Hopefully. A more accurate and reliable system was the Distributor Vacuum Control Valve, which first appeared on a few cars in 67, and by 68 Ford was using it on practically everything.

Many, perhaps all, 352 and 390 carbs had the hot idle compensator, but they were rarely if ever seen on the 289, except spliced into the PCV hose on AC-equipped cars.

Dashpot-



Hot idle compensator-


dashpot is what i was thinking but old age must have kicked in again....
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