The Ford Barn - View Single Post - Y Block Normal Vacuum w/mild Perf. Street Cam?

dw-satx · 01-04-2020, 10:59 AM

The freshly rebuilt engine (292 Y block) in my '61 F100 pickup stumbles on acceleration. The carb (Autolite 2100) fuel mixture seems to be very rich at idle and I cannot lean it out with the idle mixture screws. If I turn them out more than 1/4 to 1/8 turn, the exhaust is noticeably richer from the tailpipe. This is the same carb that was running good before the rebuild. The rebuild was all stock components except for the cam. I put a Howard cam (P/N 292002-10) back into it. Intake lift is 0.463 and exhaust lift is 0.463 with a duration of 266 degrees. I understand that the vacuum decreases as the valves stay open longer, but what should I expect with this cam? I am seeing about 5 inches of vacuum at idle. Is that normal for this engine with the new cam? I am measuring the vacuum on the carb by disconnecting the vacuum line to the distributor as I don't see any other place to tap into to measure vacuum. Is there a better place to measure the vacuum? Because of the low vacuum, I think I need to change my carb power valve to a 25 from the current 75. To my understanding the current 75 would be staying open at idle due to the low vacuum creating the rich mixture and consequently the stumble on acceleration. Vacuum does increase when I increase RPMs and stays steady until I decrease RPMs.

01-04-2020, 10:59 AM	#1
dw-satx Junior Member Join Date: Feb 2017 Location: Texas Posts: 27	Y Block Normal Vacuum w/mild Perf. Street Cam? The freshly rebuilt engine (292 Y block) in my '61 F100 pickup stumbles on acceleration. The carb (Autolite 2100) fuel mixture seems to be very rich at idle and I cannot lean it out with the idle mixture screws. If I turn them out more than 1/4 to 1/8 turn, the exhaust is noticeably richer from the tailpipe. This is the same carb that was running good before the rebuild. The rebuild was all stock components except for the cam. I put a Howard cam (P/N 292002-10) back into it. Intake lift is 0.463 and exhaust lift is 0.463 with a duration of 266 degrees. I understand that the vacuum decreases as the valves stay open longer, but what should I expect with this cam? I am seeing about 5 inches of vacuum at idle. Is that normal for this engine with the new cam? I am measuring the vacuum on the carb by disconnecting the vacuum line to the distributor as I don't see any other place to tap into to measure vacuum. Is there a better place to measure the vacuum? Because of the low vacuum, I think I need to change my carb power valve to a 25 from the current 75. To my understanding the current 75 would be staying open at idle due to the low vacuum creating the rich mixture and consequently the stumble on acceleration. Vacuum does increase when I increase RPMs and stays steady until I decrease RPMs.