hey yall i put a 800cfm edelbrock 4 barrel on my 78 f 150 it has the 351m/400 in it. it has a cam upgrade but i dont know what the specs on it are it was put in before i got the truck it also has a preformer 400 intake manifold everything else is stock.i have been told i have way too big of a carb on it so i was curious to see what i can do here can i jet the 800 to were it will work right or do i need to just get a smaller carb. and what happens when you have too big of a carb on it does it loose power?

i figured i would ask you all since you guys know a lot more than i do

thanks

 

Yeah, thats WAY to big a carb for that aplication. Only thing you can do is get a smaller one, say in the 600 to 650 range MAX. Yes, your loosing a ton of bottem end with a carb that big.

 

If you find that you have black smoke, hesitation, bad fuel economy, then you have too much of a carb. CFM rating depends on CID, Compression ratio, Exhaust system, and RPM range of the cam installed, However, should you decide to downsize the jets, and/or upsize the metering rods that restrict the jets, you can over-tune the carb. Then, also consider the life of the plugs or pistons from running on the lean side. How often do you mind changing them? Once a week, once a month, once a year? Should also mention ignition upgrades too. It's not impossible to run a carb this size on a 351/400; it depends a great deal on the whole combination that you have. Unless you have a real radical cam that wont idle under 1200 RPM and headers, I would recommend looking for a 650.

 

okay thanks i guess i will probably switch out the 800 for a 650 cfm i just put headers in the other day after the carb and it made no noticable difference and the ignitoin systym is on the to do list so thanks for the help.

 

Sure thing, let us know how the swap goes for ya.

 

I know that times are tough but if you don't mind spending some money, try a Holley 600 cfm carb and an MSD ignition. You will be surprised by the results. This is just one option.