MACKAZ

Holley carb talk.

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So, I have a 600 vacuum secondary Holley on my 4.0l Falcon motor. As expected it over fuels like a bastard. This carb is traditionally fitted to a V8 and jetted to suit from 4.9-5.7 litre engines. Anyone out there have any idea on what jets  I should try as a base? 

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What size is in it now?

Does it have a secondary metering block with jets, or just holes? I got really good at taking mine apart. They're a pretty basic carb. 

They're not cheap, but a 390 would be way more responsive on your engine. Higher air speed through the venturi would make for strong bottom.end torque.

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Tbh I won't know until I pull it down. I know a 600 works as some superstock guys were using them in the early 2000s. It did actually idle by itself dribble feeding it, but difficult to run it any longer than 10 seconds. Carbs been on shelf at Dad's for 10 years at least. Date stamp comes back as '99 as date of manufacture. 

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Can you change main jets or is it a metering block? I changed mine so could alter jets, was cheap enough kit. Been a while since I twiddled...

 

[Edit] yeah same question runamuck asked...

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It will 100% need a rekit. 

I wouldnt put too much stock in what racecar guys ran. A road car will have completely different requirements. 

In fact in more recent times (like after a book I have called "how to modify and super tune Holley  carburetors" was printed) they produced a 465cfm vac sec. Which goes well on a 5ltr v8. 

People are always overcarburating their engines. One dirt track neanderthal at work bragged how well a 900cfm carb went on some "small" ford in line 6. (Might have been a 221?)

On one engine I saw first hand a 390cfm 4bbl would light the tyres with a stock converted when given a hard stomp. Yet with a 600 it would not.  

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You can buy carb kits with re-usable gaskets that let you remove and refir the metering blocks if you're going to be fiddling lots. First test I used to do to see if it was over jetted was to get it running at a high idle, then wind the idle mixture screw in. If it winds all the way in and doesnt stall then you jets are way too big.

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2 hours ago, Thphantum said:

You can buy carb kits with re-usable gaskets that let you remove and refir the metering blocks if you're going to be fiddling lots. First test I used to do to see if it was over jetted was to get it running at a high idle, then wind the idle mixture screw in. If it winds all the way in and doesnt stall then you jets are way too big.

If the idle mixture screws have no effect, then you've got a blown powervalve diaphram. That will make it fearsome rich too.

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9 hours ago, RUNAMUCK said:

It will 100% need a rekit. 

I wouldnt put too much stock in what racecar guys ran. A road car will have completely different requirements. 

In fact in more recent times (like after a book I have called "how to modify and super tune Holley  carburetors" was printed) they produced a 465cfm vac sec. Which goes well on a 5ltr v8. 

People are always overcarburating their engines. One dirt track neanderthal at work bragged how well a 900cfm carb went on some "small" ford in line 6. (Might have been a 221?)

On one engine I saw first hand a 390cfm 4bbl would light the tyres with a stock converted when given a hard stomp. Yet with a 600 it would not.  

Funny you say that re the 465. My old man farked around for moons with a 600 on his 302, the experts had a few goes. The old man one day said fark it went a brought a brand new 465 bolted it straight on outa the box. Fark me what a different car! Drives so much better uses heaps less gas. So agree bigger is not always better!

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Check the jet sizes too, and float level?

From memory I think you won't want to be much more than a 72 mains, cant remember what the idle jets were

Edit, 65 will be closer for a stock engine

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 I have a 500cfm on a mild 318 and that works very well. Originally I had an engine with a 500 two barrel holley but wanted a 4 barrel with smaller primaries so it would run more efficiently 

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Stripped it down this afternoon. Someone's been in there before. Factory mains listed are #66. It has got #60 in it. Spoke to old boy today and he cant remember where he got it from. So at a bit of a loss as to what it was feeding. 

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@MACKAZ

I was just going through my Impco lpg carb book looking for something else and spotted the formula to work out the cfm of your engine at a given RPM.

It's CID x RPM / 1728 /2 x .85

So 250 CID x 5000RPM (Optimistic) = 1250000

1250000 / 1728 = 723.4

723.4 / 2 =361.7

361.7 x .85 =307.4

Your 4.0 will sip about 310 CFM at 5000 rpm 

I'd put the 600cfm on TradeMe and put the money toward a more suitable carb.

As a side note. Big carbs on small engines tend to run lean. They dont generate enough vacuum in the venturis to draw fuel out of the main jets. People put large jets in them to try and overcome this but the idle and transition becomes very unstable. 

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Thanks for the info. I'm still going to run it as I can't sell it, due to being given it by the old man, and I wont get the money back for the kit. 5000rpm with a 4.0l on carb is a not that much. 

The whole shit idle and transition appeals to me. I don't care about efficiency or the engine. If it blows up it blows up. This one is a mule to see if I can get it to work, and, it probably won't, then I'll find a Weber and put on it. I know they feed a 4.0l in excess of 5000rpm

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Nothing worse than a oversized and old holley carb, throw it in the bin.

Ask Bort about opportunity cost and sunk cost fallacy.

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Sure is, and I reckon its great OMG, WTF, Bbq material. No different to putting 45DCOEs on a Kent 1600

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