Carb too big??Now what?

[The_Dealer]

Well i bought a holley carb from a buddy, he told me it was a holley 350cfm, and reading the numbers and matching them up in my summit book, i actually got a holley 500...ok so thats way to big for my 2.8 to utilize. So the question is, what is the difference between the 350 and 500? is the body the same? i know the 500 has 50cc accelerator pump. basically can i rejet my 500 to work like a 350 on my motor? i would like to keep the carb because when i go to do my 5.0 swap i can put it on that motor too.

 

[dangerranger83]

Does your truck run good with it on it or have you put it on yet? If you haven't put it on yet and your truck runs, I wouldn't bother changing it. Try to find a motorcraft carb. with 1.08 venturis in it. I got mine off a 3.8 liter from the j/y but they can also be found on 5.0s too. My dads came off a 255 v8 (I can only imagine how much of a dog that engine was).

 

[Big Jim M]

Even the 350 is actually too large for your engine. I wouldn't keep that carb, I'd try to swap it for a motorcraft with the 108 venturi in it.
Large carbs don't work well at all for normal driving. The reason is the flow in the thing is too slow and it simply cannot work as designed. Carbs depend on a planned VELOCITY of the flow. If the engine cannot produce that VELOCITY the carb is lost.. It cannot do it's job.
Big JIm

 

[The_Dealer]

havent put it on yet, although i do know it was used on a 2.8 with an offy, before a 650 took its place. he said it ran pretty good on the 2.8 but ran kinda rich

 

[Big Jim M]

I'm not gonna make a graph

havent put it on yet, although i do know it was used on a 2.8 with an offy, before a 650 took its place. he said it ran pretty good on the 2.8 but ran kinda rich

I highly doubt that engine could POSSIBLY use all the cfm in the front barrels of a 650! At 5,000 that engine is prolly usiing around 225 cfm. Just a guess but I'm close! Remember carbs work on VELOCITY.. The less velocity thru larger barrels the worse the carb will perform. A too small carb is far more usable than a larger one.
The usefulness of a too large carb is limited to 1/4 mile runs!! On the track where the engine must perform at all rpm that too large carb must be replaced with one that will WORK!
Big JIm