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Vd=0.7854B2S, CR=Vd+Vc/Vc
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Discussion Starter · #1 ·
I just bolted one of these on my 383 vortec, i had to turn the idle mixture screws out to 3 turns to make it run desent at cruze without missing, this of course made it eye watering rich at idle. Base jetting on the primarys is 72s, i picked up some 74s and 75s. and hopfully i can get the idle mixture down to 1 to 1-1/4 turns out. i was suprised when the parts guy handed me holley jets.
Anybody out there rejetted the 750 slayer and how'd that go? comments welcome on this carb it's new to me.
 

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I had a quick fuel 600 slayer on my 350 and it was very rich out the box. As far as jetting goes I was able to go down on mine and had no problems. But mine is a 600 not the 750. My 350 has dart shp 180 heads, high dual plane intake and 219/227 @ 50 515/530 lift voodoo roller cam so nothing real wild. I am surprised yours is actually that lean but it would help a lot of what your engine specs are.

I damaged my metering block on my 600 and got a replacement from quick fuel and they use the same blocks on both carbs as the one they sent me had 72 jets already installed in it so I had my old one and they match both the same so the idle circuit on the blocks should be good to go maybe you just need to jet up.

Is this while cruising under 35mph like around town or highway? If highway then jetting would be the key to tune but if town driving then that would be the transition circuit. According to what I could find the 750 has the same air bleed size as the 600 and with the bigger throttle bores and with the same air bleeds as the 600 I would think that would make it a little lean since it has a lot more air down the venturi.

I could be wrong but the expert tuners in here should be able to give more input. I would reset everything back on the carb to specs and make sure your transfer slots are opened correctly and also your timing is correct for your setup. That makes a lot of difference too as too much timing can cause what seems like a carb issue. Turning the idle mixture screws out that much wont really affect cruising going down the highway. It mainly is idle and off idle and that's it.
 

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I am considering a quickfuel carb for my next build.
Quickfuel has a website with tech info on how to tune the carb.
I think you need to set your idle back where you had it and put in smaller High speed air bleeds to richen it up at cruise . WOT is enrichend by the power valve.
Go to the Quickfuel site and go to the tech section and checkit out. It explains how.
Keep us posted , as I said i like the idea of the quickfuel as they are suppose to be easy to tune.
Also the fully adjustable secondary vacuum diaphram is a real nice and easy to adjust.
 

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Vd=0.7854B2S, CR=Vd+Vc/Vc
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273 Posts
Discussion Starter · #4 · (Edited)
I don,t have QFT air bleeds on hand but....

I could try some really fine wire, secure that as a restrictor down in the hi spd air bleed passage, if the motor runs better, I'll know I need to step down. Now correct me if i'm wrong but if this was a Holley with non changeable air bleeds wouldn't the correct solution be to go to a bigger main jet? is not changing the air bleed just an easier way to achieve the same result with out having to take the carb apart?
When the idle screws are at 1-14 turns out the engine idles pretty nice and just snaps amazing on the throttle.

pri main is 72 secondary is 82

idle air bleed is 70/39 hi spd air is 31/31 power v/v is 6.5

so 70 and 39s are on the outside primary and secondary's respectively
and 31 and 31 are on the inside primary and secondary's respectively.

Heads are flow bench ported, cam is 270 magnum, ignition is locked at 33* compression 9.75:1, 7/8 inch 4 hole carb spacer
 

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Vd=0.7854B2S, CR=Vd+Vc/Vc
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273 Posts
Discussion Starter · #5 ·
Re-jetted the mains anyway

I Re-jetted the mains anyway, to see what that would do, I went to 74s which helped a bit and then I put in the 75s which made it some what driveable, but it needs further development not much change. I got the idle mixture screws down to 1-1/4 turns out, so it's not loading up at idle, and there is a random miss at cruzing speed.

Holley jets fit this carb but they are not the same as QFT. The QTF jets have about a 15* tapper on the inlet side were the Holley jet is flat. the QTF jet on the exit side is tapered as well maybe 20* were again the Holley is flat, I have a Holley 72 for measuring and both the Holley and QTF jets measure 0.070' within 0.001

I'm thinking Holley and QFT jets are not strait up comparable. QTF jets probably flow more, and the 75 Holley I put in may be like a QTF 73 .
 
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