alittle guidance appreciated on 850 holley

Hello all. I have a question. I have been running a holley 750 dp on my 505 with no power valves, thats the way i bought it. now i have purchased the new holley 850 ultra hp. It came with a 4.5 power valve. I do not see any vacuum ports on this carb nor do I need any i do not run power brakes or vacuum advanced dist. Now I was wandering how to get a vacuum reading to find out if that will be the correct power valve. Also on my old carb I was running 79 jets in front and 82 in back. I have read that if I run a power valve my jets should be bigger. I noticed the 850 came with 84 in front and rear. thanks for any info, tips or tricks with this new carb.:eek:

your intake as no vacuum ports .what did the engine have for vacuum in gear at idle with old carb ? then that would be were you could start i cut the reading in 1/2 so lets say you had 8 inchs of vacuum in gear i used a 4. or4.5 power valve if less then 3 inchs at idle i plug them then jump up on jets size so if you plug the power valves in the new carb any were from 90 to 94 i would start on the smaller size jets.if race stuff i just plug the power valves

Thanks pat. I have never checked vacuum with old carb. But I will before I remove it. This motor is just for mud bogging and ridding trails in the woods. I am running a manual trans. I try to do as much research as possible le before asking questions and more times than not it will redirect me to a post on this forum so I figured it has to be a good spot to ask questions. Will the power valve plug out of my older 750 holley double pumper work with this new 850 ultra hp?

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Originally Posted by 505onrocks

Thanks pat. I have never checked vacuum with old carb. But I will before I remove it. This motor is just for mud bogging and ridding trails in the woods. I am running a manual trans. So I would check my vacuum in neutral correct. I try to do as much research as possible le before asking questions and more times than not it will redirect me to a post on this forum so I figured it has to be a good spot to ask questions. Will the power valve plug out of my older 750 holley double pumper work with this new 850 ultra hp?

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yep your power plugs will work in the new carb how big is the cam at 050 . if you had power plugs in it before then you may have low vacuum ? what ever you have at idle i have aways drop down under max vacuum at idle on power valve size by 1/2

Thanks again pat. I do not know the specs on this cam. I destoyed my first 505 that I knew all the specs on and had dynoed. I bought this engine already assembled from a friend. Im not sure if i know what you mean by how big is my cam at 050. ? If that means duration@ .050 I think i am around 262/273.

if that big @050 on dur i would go to just power valve plugs

I mostly run new Holleys right out of the box without major adjustment..I'm not sure how they tune them at the factory..but they do run exceptionally well right from the box.
I feel most guys get less performance the more they play with the jets and valves.
I would seriously live with your new carb for a while before modding it.

hard to get them to run great out of the box if you have a 250+ @ 050 cam they do run ok out of the box on mild stuff He is far from mild