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| GTBob |
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Leave the choke setup but take out the plate as this makes for a very handy fast idle device which can be quite handy at times. as for cutting off the housing this can have some strange effects on idle circuits so be carefull I have had all manner of holley combinations and as said 600cfm vac secondary is good until you start adding large cams phase 3 gtho came with 750 vac secondary from showroom.
 
Also the secondaries should be held closed by the spring in the vacuum chamber and not bind in the throttle bore
_________________ Rotten Old Revhead!!! XW GTHO + EF ex cop car (exractors 2.5 cat back zorst !6" Simmons K&N +airbox mods Lowered with Bilstein shocks+Whiteline Bars NEXT THING Swap HO for GTP or Ferrari! |
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| 351EL |
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Leave the choke on as you live in tassie.
If you lived where i do i would take it off.
_________________ Smoken the hides in top gear |
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| Mac Winter 76XB351GS |
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I cant be stuffed taking the choke off, I'll leave it on there and secure it if we find I dont need it.
What do you gain from taking it off? Not going to but would like to know.
_________________ 76XBGS, 383c, custom crow cam, 4V p&p heads, Isky SS Valve+springs, extractors, 2.5"twins, MSD Ignition, Edelbrock intake, Forged bottom end, Barry Grant 750DP, thermo, discs, toploader, Holley fuel pump, SUPERCHARGED! |
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| Walker |
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{USERNAME} wrote: phase 3 gtho came with 750 vac secondary from showroom.
A 780 actually, and that's a 750 with a metering block on the secondary side of the carb. I cut my choke shroud off completely, it was one of those common things we did, removing any restrictions. My car ran fine without it, i bought the carb to replace the 650 DP when i went back to auto and removed the shroud before fitting it. |
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| Samsy |
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I run my 600 without choke.
_________________ XB 351 and BA GT |
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| Fakertaker |
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600 Should be fine (just echoing what was said above). I have a decent cam, mild headwork, single plane manifold and extractors and all the rest. I run a 650 DP which in my opinion is still slightly too large for my needs. The 750 will only become usefull once you get some serious work done. Good luck with it all!
_________________ Oversteer - The only way to steer |
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| Mac Winter 76XB351GS |
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Well I got it all on and tested both carbs out and the 750 vac sec is by far the better performer, but uses a heap more fuel
 . I cant believe how well it goes now. More good news, the std intake is in top nic, looks brand new bescides a bit of grease, 600 just needs a polish and thats in A1 too.
Ive got an ignition problem between 2200 and 3000 which is giving a slight knock. Looks like I'll be switching over to a MSD elec ign soon, hopefully something with adjustable curves $$$. Thanks for all the help. Anyone want the manifold and 600???
_________________ 76XBGS, 383c, custom crow cam, 4V p&p heads, Isky SS Valve+springs, extractors, 2.5"twins, MSD Ignition, Edelbrock intake, Forged bottom end, Barry Grant 750DP, thermo, discs, toploader, Holley fuel pump, SUPERCHARGED! |
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| Walker |
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You sure it's not the BOARRRRRRRRRRRRRRR from the 4 barrels sucking in thats giving you an illusion of more grunt? (Yes it does happen lol)
Give it a week and take your dip stick out, if it has a strong smell of petrol i'd say she's getting too much lol. I'm not sure if you are aware but that washes the oil from the bores and shortens your engine life in a big way, you are basically washing the rings away. I'm only saying this as my clevo had a fair bit of head work, rollers with big cam, single plane Weiand intake, balanced and blueprinted, ARP rod bolts blah blah blah and the 750 was def pumping too much fuel in. A 650 would have been much better. Good luck mate, i hope you sort it all out. |
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| Mac Winter 76XB351GS |
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If I could hear the carby Im sure it would sound tougher than the 600 but I cant hear a thing over the exhaust
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The 750 has been jetted down a little, not too sure what it is equiv 2. I'll take a whif of the oil and see what its like. The car feels a lot smoother and doesnt bog down like it used to. I might have to jet it down a little more if things dont look good in a few weeks. Might just hang onto this 600 untill im sure the 750 is doing the right thing. Thanks for the heads up on the overfueling. Will keep an eye on it. 
_________________ 76XBGS, 383c, custom crow cam, 4V p&p heads, Isky SS Valve+springs, extractors, 2.5"twins, MSD Ignition, Edelbrock intake, Forged bottom end, Barry Grant 750DP, thermo, discs, toploader, Holley fuel pump, SUPERCHARGED! |
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| earlybird |
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After a quick calculation the best possible carb size would be a 650 cfm carb, assuming that the engine has a redline of 6500 rpm. Very advisable. The cleveland engine has some serious problems after this speed. The 600 cfm holley will do great for a mild street engine but will run out of puff further towards 5500 6000 rpm. A 750 will be too big for a street engine and the price of fuel as it is now you can't afford to blow unburnt fuel out the exhaust. Personally i would trade the two carbs in and get a 650 vac secondary holley. works perfect on my xb 351
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| samftr |
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{USERNAME} wrote: I picked the performer intake and 750 today. It turns out its a vac sec not a double pumper, which is good because Id rather that. It looks so damn nice, all clean with its little fuel pressure gauge. Im thinking as it is already mounted on the intake, I'll put it on as is and then swap the jets over to suit the motor as it is now and then I can just swap the jets back when I do the heads and cam if it needs it.
Just a little question though. On the vacuum side of the carb there is an arm to open the secondarys, it looks as though there is supposed to be a spring going from the arm and attaching to a small swinging link fixed to the vacuum diaphram housing. Does this sound right, because there is no spring there now and the secondarys dont want to close unless you lock them open then give them a tap, when which, they snap shut. See pic. Also are there supposed to be plugs in the fuel ports on the side of the carb not being used, or are these sealed by the large screws in the centre of the carb at each end? see that carbie there, what is the smallest size that it comes in - looking like that. i had a 202 s**t box vk with a holley on it but im not sure what size it was, no wonder it was s**t on fuel!
_________________ 175.7hp 15.5 @ 374,000km
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