New carb makes all the difference
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More Turbo
Joined: Dec 1999
Posts: 582
Likes: 5
From: New Orleans United States
New carb makes all the difference
Well, I finally decided to spend the cash and go to a carb correctly sized for my engine.
I have a 400 in my 77 F150 4X4 and since building the engine about 10 years ago, it has had a Holley 750 CFM Vacuum secondary carb. It had always idled rich, was picky about jets and would have absolutely no bottom end power below about 2000RPM. Power braking it would just result in the engine not going over the torque converters stall speed since it was out of the power band of the big carb.
So my financial situation allowed me to buy a 600 CFM Holley Vacuum Secondary and just put it on the truck the other day. It now idles much more smoothly, and can either light up the rear tires, or push the front end down the street from all the new low end power it has. I haven't had a chance to take it out on the open road and really see how much more responsive it is at part throttle due to rain and road construction around the house.
I'm sure it needs to have all the carbon blown out since it has run rich for so long. New plugs are already in place and I am sure they are much happier than the old set that came out.
The lesson is bigger isn't better when sizing a carb. Manifold vacuum and venturi flow is key to the carb acting correctly, and I now understand exactly how much.
I have a 400 in my 77 F150 4X4 and since building the engine about 10 years ago, it has had a Holley 750 CFM Vacuum secondary carb. It had always idled rich, was picky about jets and would have absolutely no bottom end power below about 2000RPM. Power braking it would just result in the engine not going over the torque converters stall speed since it was out of the power band of the big carb.
So my financial situation allowed me to buy a 600 CFM Holley Vacuum Secondary and just put it on the truck the other day. It now idles much more smoothly, and can either light up the rear tires, or push the front end down the street from all the new low end power it has. I haven't had a chance to take it out on the open road and really see how much more responsive it is at part throttle due to rain and road construction around the house.
I'm sure it needs to have all the carbon blown out since it has run rich for so long. New plugs are already in place and I am sure they are much happier than the old set that came out.
The lesson is bigger isn't better when sizing a carb. Manifold vacuum and venturi flow is key to the carb acting correctly, and I now understand exactly how much.
