i have a 78 ford f150 4x4. has a 400 in it bored 30 over, aggresive cam, headers, ported and polished heads, straight up timing set, weiand intake, roller rockers, and 600 holley vacumn secondary carb. the carb is just worn out, the guy i got it from rebuilt it at least 100 times if he did once and it worked great for awhile now i'm afraid it's shot. I was thinking of putting a 650 or 750 double pumper on it in place of this carb i have now but i don't know if they will be too much for my motor or not. the truck is a 4 speed, 3.55 gears and 33" tires. i know on summit.com it says double pumpers are best for vehicles that are light ( 3100lbs to be exact) and i know my truck is heavier than that i think. any help is greatly appreciated

 

I would use a 750 becouse the larger carb tends to be less sensintive to the venturi effect on long stroke motors like your 400.

The 600 is easily upgradeable to 750 vac sec but it should be done by a profession shop like PC carb in Ontario Ca. For the same cost of a basic new carb you could have a fully massaged custom built one.

 

You'll want a vacuum secondary carb for sure. More response down low, not to mention much better fuel economy.

I would say the best advice is to have somebody else rebuild your carb. They are very simple to rebuild and if the throttle shafts are worn they can be replaced and the carb body re-bushed no problemo.

I recommed an Edelbrock Performer or Carter AFB 600 cfm carb myself.

Josh

 

He says he has an aggressive cam, and they usually do not like vac sec.

 

thanks for the replies guys. i would rather not mess with the carb i got. the driver side idle mixture screw does not change the idle, it stumbles and has a bad dead spot and the secondaries will sometimes stick and not open. It seemed to run fine with it at first but always seemed like it wasn't enough carb.

 

800 cfm Rochester Quadrajet is my choice.

 

My Dad worked at Holley for 42 years. I have owned my 79 f-100 for 26 years and had several popular version of Holley carbs on my modded 351-m. The #1850, #3310 and #4776 run the best. The 1850 is a 600cfm vac sec that has the best start and idle. The 3310 is 750cfm with vac sec and the 4776 is 600cfm with manual sec double pump. All of them will work great for you. I run the 1850 now because I can get a little mpg and the idle is just a little better. I can set the electric choke and it with start and idle like a FI engine.

 

??? That has nothing to do with it.

If you're dead-set on a double pumper then by all means get one. But you'll be happier, be it engine or you're wallet, with a vacuum secondary carburetor.

I can claim all day long how aggressive the cam is in my lawnmower, but if it doesn't rev over 3500 rpm there is no need to slap a huge carburetor on it.

The 400 with it's anemic intake and cylinder heads isn't going to utilize the full potential of a 750 double pumper, unless the engine is revving past 6000 and has 10:1+ compression.

Also, it isn't so much a matter of how much a vehicle weighs with a DP carb, but it needs steep gears.

Josh

 

yeah you make a good point Bullitt. i'm not dead set on a double pumper i was just thinking it would work better in my truck than what i have.
tod79_351 listed some good carbs i'm goin to check into them, i just don't think that the 600 is big enough or that may be because mine was junk to begin with

 

2x with Bullitt390 on sizing. A 600 to 650 cfm would be fine for your engine and assuming that your typical RPM range is idle to 4000.

Plus with a 4-speed, you'll be wasting fuel with a double pumper since all four barrels are working each time you shift. With a vac secondary, the other two holes will only get fuel when the engine load says it is needed.

 

A 600cfm would be plenty bug for your engine. Remember, big cams, valves ports make a engine have low rpm hp numbers. If you get a double pumper, get one no bigger than the #4776 or #4477. My 4776 ran great. Good Luck with what ever you pick!!!

 

what about one of these street avengers? i found a 670 vac secondary that looks like it would be perfect. anyone have experience with these carbs?