MACKAZ Posted August 23, 2020 Share Posted August 23, 2020 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? Quote Link to comment Share on other sites More sharing options...
RUNAMUCK Posted August 23, 2020 Share Posted August 23, 2020 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. 1 Quote Link to comment Share on other sites More sharing options...
MACKAZ Posted August 23, 2020 Author Share Posted August 23, 2020 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. Quote Link to comment Share on other sites More sharing options...
Lord Gruntfuttock Posted August 23, 2020 Share Posted August 23, 2020 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... Quote Link to comment Share on other sites More sharing options...
RUNAMUCK Posted August 23, 2020 Share Posted August 23, 2020 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. 1 1 Quote Link to comment Share on other sites More sharing options...
Thphantum Posted August 23, 2020 Share Posted August 23, 2020 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. Quote Link to comment Share on other sites More sharing options...
UTERUS Posted August 23, 2020 Share Posted August 23, 2020 Tl;dr Sounds like a job for a Predator carb. 3 Quote Link to comment Share on other sites More sharing options...
Nominal Posted August 23, 2020 Share Posted August 23, 2020 19 minutes ago, UTERUS said: Tl;dr Sounds like a job for twin SU's. 2 Quote Link to comment Share on other sites More sharing options...
RUNAMUCK Posted August 24, 2020 Share Posted August 24, 2020 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. 2 Quote Link to comment Share on other sites More sharing options...
MACKAZ Posted August 24, 2020 Author Share Posted August 24, 2020 I'm pretty sure the kit I've ordered has a new power valve assembly in it. https://www.proparts.co.nz/shop-online/air-fuel/parts/carb-kit-holley-450-600cfm-4bbl-vac-sec-sq-bore-detail.html Looks pretty complete Quote Link to comment Share on other sites More sharing options...
rusty360 Posted August 24, 2020 Share Posted August 24, 2020 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! 1 1 Quote Link to comment Share on other sites More sharing options...
CUL8R Posted August 24, 2020 Share Posted August 24, 2020 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 Quote Link to comment Share on other sites More sharing options...
Lord Gruntfuttock Posted August 24, 2020 Share Posted August 24, 2020 I bought 64 and 66 jets for a warmed up 302. Not sure how small you can go with a 600... Quote Link to comment Share on other sites More sharing options...
cletus Posted August 24, 2020 Share Posted August 24, 2020 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 1 Quote Link to comment Share on other sites More sharing options...
MACKAZ Posted August 29, 2020 Author Share Posted August 29, 2020 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. Quote Link to comment Share on other sites More sharing options...
Valiant Posted August 29, 2020 Share Posted August 29, 2020 @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. 6 Quote Link to comment Share on other sites More sharing options...
MACKAZ Posted August 29, 2020 Author Share Posted August 29, 2020 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 Quote Link to comment Share on other sites More sharing options...
Spencer Posted August 29, 2020 Share Posted August 29, 2020 Nothing worse than a oversized and old holley carb, throw it in the bin. Ask Bort about opportunity cost and sunk cost fallacy. 1 Quote Link to comment Share on other sites More sharing options...
Lord Gruntfuttock Posted August 30, 2020 Share Posted August 30, 2020 Nah this is Old School. Doing dumb things with old gear is great. I reckon you're way overcarbed but interested to see how you get on... 3 Quote Link to comment Share on other sites More sharing options...
MACKAZ Posted August 30, 2020 Author Share Posted August 30, 2020 Sure is, and I reckon its great OMG, WTF, Bbq material. No different to putting 45DCOEs on a Kent 1600 1 Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.