Hi,
I have a 1978 F100 4x4 truck.
It has a 750 on it at the moment, Which needs rebuilding.
Should I just get it rebuilt or buy a 600.

Would like to improve fuel economy.

Thanks,

 

Depends whether you want the extra cost of a new carb versus just rebuilding your current one. You also don't mention what engine you are running.


Regardless, all other things equal, a smaller primary venturi will give you better fuel economy as it will have a much higher flow velocity and better atomisation of the fuel into the air stream. This is part of the reason that the Holley 460 'Economaster' works so well - it has tiiiiny primary venturis and atomises the fuel very well.


So, what engine do you have and would you mind paying for a new carb?


- boingk

 

Hi,
I have a 1978 F100 4x4 truck, Cleveland V8 351.
It has a 750 on it at the moment, Which needs rebuilding.
Should I just get it rebuilt or buy a 600.

Would like to improve fuel economy.
Does having a 750 providing it is rebuilt any different to the 600, also providing the truck is driven carefully.

Thanks,

 

Ah nice, Cleveland 351. Popular engines down here in Australia!


The 750 is probably a tad too big for the 351 unless you are running it at 6,000rpm. Do you have any modifications to the engine or is it stock?


The 600 would work well for economy and still let you have good performance. If you find a Holley 'Economaster' 450 it would work just fine as well, especially if you don't run above 3500rpm too much and mainly rely on strong midrange power.


- boingk

 

I am pritty sure the engine is stock.
(It sits on 35's and has a lift kit, does that make for 750 requirement?
Hope to get smaller tyres eventually 31's)
You answered the question I was tring to ask.
Dont want to invest in the old carb if 600 would be better.
Not sure where I could get one from?

By the way I also have slop in my power steering box.
Not sure where I can get one of them from iether?

Thanks,

 

Hmmm not sure on the power steering box. Sorry.


The best way to think about it is the engine will only use a certain amount of air - its best to pick a carburettor that will meet this requirement and not exceed it. Anything larger than you will use will only slow down the airflow going into the engine, causing tuning problems or poor economy.


Big tyres would like to see lower differential gears like 4.10's instead of 3.50's as the bigger the tyres are the slower they turn for a given speed, and the engine has to turn slower to try and drive them that speed. Adjusting either tyre size or differential gears will put everything back working right again.


Here is a 600cfm Holley-style carb from Summit Racing. $200 delivered and seems to have positive reviews.


https://www.summitracing.com/int/par...00vs/overview/


The major benefit you get with having a new carburettor is that is has already been calibrated to work in 90% of situations, especially stock or mildly modified engines, and is designed to be run straight out of the box with little or no modification.


I've bought a very similar carb and found all I needed was a power valve to help with a slight hesitation when I tried to overtake on the freeway, other than that it was perfect and idled straight out of the box. My economy on the freeway went from 18mpg at 70mph with the stock 2-barrel carb to 23.5mpg at 70mph.


- boingk

 

Hi,
took your advice, got the carberetor. Its on the truck.
The studs were too short for the carburetor and gasket that came from summit. So, I want to rectify that. Do you know where I can get longer studs from? Cant beleive it though. Not as bad, but I still get the over rev issue.
Will make a bracket to move the spring to the other side of cable.
Thanks,

 

600 either Holley or Edelbrock will make a happier combo in a big heavy 4x4 with a 351. I ran a 600 Holley for over 25 years on mine, rebuilt it a few trimes ..... swapped to Edelbrock 600 (1405) a couple - 3 years ago. Either one was a plenty om my 351 4x4.

You said it's a Cleveland, it's stock .... likely you have a 351M which is a member of the same family as the 351C. The 351C was first, then the 400C came out in '71, then Ford wanted a smaller CID version of the 400, hence the 351M. Heads interchange, valve covers look same, they are different though inside and out many ways. 351M is just a destroked version of the 400.

As to steering boxes, I have a '77 4x4 power steering (& oem 351M) that I've had since 1986. I improved steering in 1986 by updating linkage to '78-9 style, but for years put up with vague steering still even though bump steer was gone. Few years ago, caught a group buy here on this sight and got $60 off on a Red Head Steering remanufactured / improved box. The improvement was huge. They shipped it from Seattle, Wa. to here in Va. in two days. I shipped my core back and in less than a week had my core charge refunded.

https://www.redheadsteeringgears.com/

 

Boingk and the OP are in Australia - I understand Ford made Australia specific 351 engines for our dents that are more 351C than 351m.