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4100 rebuild questions

1K views 8 replies 4 participants last post by  carlite65 
#1 ·
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?
 
#4 · (Edited)
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-

 
#3 ·
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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