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  • Aight carb gurus

    So, im trying to decide which carb would be better, using the same ole calculator i end up at a 720cfm. So in the middle between a 680 and a 750. Car is a street car with a 460hp 383. Not interested in double pumpers. What size would you run? Yea its a street car but i do get on it regularly..so 750vs or 680vs.. cam is a 231/[email protected] 111+4 icl.

  • #2
    750 vac secondary should be almost big enough, but not quite...

    My fabulous web page

    "If it don't go, chrome it!" --Stroker McGurk

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    • #3
      I'm personally thinking of trying one of these next: https://www.hotrod.com/articles/stre...0-carb-review/
      Patrick & Tammy
      - Long Haulin' 2008, 2009, 2010, 2011, 2012, 2014...Addicting isn't it...??

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      • #4
        Originally posted by squirrel View Post
        750 vac secondary should be almost big enough, but not quite...
        So my 670(which is really a rebranded Qf 680) is too small?? If so that explains the absolute hell ive had tuning it!!

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        • #5
          Usually a too-small carb won't be hard to tune, it just won't make as much power as you could with a larger carb.

          My fabulous web page

          "If it don't go, chrome it!" --Stroker McGurk

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          • #6
            Cool, yea the engine builder recommended the brawler 670, but he also sells those so..I seen an episode of Engine masters and the engine was really similar to mine, and the 750 did the best. I also talked to a friend thats been building hotrods longer than ive been alive and he said the same, the 670 is too small, said to get a 750vs for the street or a 750dp if i race alot(which i dont).. Reason i ask is im really interested in the new FST 750vs carbs..

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            • #7
              I dont know what they did with that carb they decided to name brawler, it was terrible when that new diecast first came out. I know its been 5 years or so, but I guess its simple if you get exactly what you need.

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              • #8
                Originally posted by anotheridiot View Post
                I dont know what they did with that carb they decided to name brawler, it was terrible when that new diecast first came out. I know its been 5 years or so, but I guess its simple if you get exactly what you need.
                This carb had 680 stamped on the main body, and everything else looks identical to a 680 hr i had. With that said, this has been the hardest carb ive ever had to tune, not really sure why either. The main issue was aean spike on transfer at light throttle. If i richened it up to eliminate the spike, then it was way too rich. After countless attempts, i finally drilled the primary blades, and so far its helped. Now i can open the mixture screws more to eliminate the spike, and idle afr is now 13.3, which it use to be 12.3 at idle. Idk, its been a pita for sure..

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                • #9
                  Oh...you want the numbers to look good, in addition to having it run good.

                  I settle for running good.
                  My fabulous web page

                  "If it don't go, chrome it!" --Stroker McGurk

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                  • #10
                    Not necessarily, but to me 12:1 on the idle circuit is waay too rich..ive tuned tonwhat the car likes and it doesnt like anything leaner than 14 :1,.. at 12:1 my plugs are black, it stinks, and it loads up.

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                    • #11
                      Originally posted by Lit549 View Post
                      Not necessarily, but to me 12:1 on the idle circuit is waay too rich..ive tuned tonwhat the car likes and it doesnt like anything leaner than 14 :1,.. at 12:1 my plugs are black, it stinks, and it loads up.
                      Thats where it goes, nothing advancing the timing a degree or two might clean up, or a hotter coil, new MSD box, etc etc. Yeah, I have dealt with industries that get too much money tied up in a die to give up on a poorly designed casting so they keep trying to sell it. In this case, give it a new name. I see the advertisements where they are putting regular holley metering plates on it, which is why I do not know if they have it fixed or not, but I got one with a week of running on it if I decide to give it another shot.

                      If the engine builder suggests it, he can put it on and tune it to your liking I guess, but there is definitely going to be one of low, midrange or top end that you wont like.

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                      • #12
                        Originally posted by anotheridiot View Post

                        Thats where it goes, nothing advancing the timing a degree or two might clean up, or a hotter coil, new MSD box, etc etc. Yeah, I have dealt with industries that get too much money tied up in a die to give up on a poorly designed casting so they keep trying to sell it. In this case, give it a new name. I see the advertisements where they are putting regular holley metering plates on it, which is why I do not know if they have it fixed or not, but I got one with a week of running on it if I decide to give it another shot.

                        If the engine builder suggests it, he can put it on and tune it to your liking I guess, but there is definitely going to be one of low, midrange or top end that you wont like.
                        Yea man, ive tuned thid thing till im blue in the face. Ive tuned alot of holly style carbs and this one has been the hardest. Its ok though, i just ordered a Fst 750 vs carb and ill see how it is..

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                        • #13
                          Aight guys, i linstalled a 750 vac sec prof form carb.. This thing has a WAY better fuel curve everywhere excpt idle.. Im super happy that i made the switch, the 670 brawler was actually too rich everywhere.. One question, do yall thi k 12.6 afr is too rich at idle?? Ive tried all the way up to 13.6 and it just starts running rough‍♂️ Its rich at idle as i can smell it, but it idles decent at the richer setting.

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                          • #14
                            Click image for larger version

Name:	Screamin_Demon_750_VS.jpg
Views:	54
Size:	1.37 MB
ID:	1305965

                            I went from 650 Speed Demon VS to a 750 Speed Demon VS.
                            Stripped out two helicoils for the front float bowl, you canīt get a replacement body so I
                            tried to order another 750, none available, so I went over the top and bought a 750 Screamin Demon VS no choke.
                            Itīs taken some time to tune but I really like it.
                            It likes to idle around 12.1 but I have to lean it a tad for the yearly inspection, which it doesnīt like too much.
                            Starts first time too.

                            Bigger...ish is better.

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                            • #15
                              Originally posted by malc View Post
                              Click image for larger version

Name:	Screamin_Demon_750_VS.jpg
Views:	54
Size:	1.37 MB
ID:	1305965

                              I went from 650 Speed Demon VS to a 750 Speed Demon VS.
                              Stripped out two helicoils for the front float bowl, you canīt get a replacement body so I
                              tried to order another 750, none available, so I went over the top and bought a 750 Screamin Demon VS no choke.
                              Itīs taken some time to tune but I really like it.
                              It likes to idle around 12.1 but I have to lean it a tad for the yearly inspection, which it doesnīt like too much.
                              Starts first time too.

                              Bigger...ish is better.
                              Right in, i appreciate it. Ive also found that ya have to find a happy medium with how it runs and the afr #'s. If ya shoot for the perfect numbers youll pull your hair out trying..

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