Quadrajet carby help ?

[prado_boon]

Hi guys, does anyone know how to tune a quadrajet correctly ? I need some help in getting my secondaries to not bog the engine down. It's really fine tuning but it's driving me crazy trying to find decent help!



Cheers,
Tim (chch)

[Dirtydog]

ill have a chat to my uncle if you want, hes a holden nut, has been for about thirty years.

hes pulled apart several engines etc, so he should know atleast something.

[klompy]

Google or youtube have really good info.

[Heath]

Amazon have a couple of books on Rochester quadrajets that are as close to a bible on them you can get (cost me about 50 for both delivered to my door - cheaper than buying just one in NZ )

Rochester carberators by Doug Roe

How to rebuild and modify rochester quadrajet carburetors by cliff ruggles.

http://www.vetteprojects.com/kstyer/quadrajet.htm

google can produce a pile of info but be prepared to wade through tonnes of redneck utube vids (some are worth it) and piles of junk. There are jems tucked in there sometimes.

Heath

[Heath]

is that your carb in the video? looks like a pontiac one (had huge cuts in the flaps) they discontinued that style because they allowed too much air in before fuel flowed.

I could guess and send you down a tonne of paths but best bet would be to consult a pro or try asking the question on NZV8 or a hot rod forum. Dont let anyone tell you they are quadrajunk, they are potentioally the best option for street and strip - nice and smooth on the little 1 inch primaries and thristy as buggery when the 2 inch secondaries open up - usually.

[Heath]

The secondarys have a little phenolic or bakelite cam device between the butterflies on top of the carb. Its main(only) function is to open the jets in the secondary circuit. Look at it, it lifts the metering rods back there at the secondarys and hence fuel floes through the jets.That is how the secondary cicuit is metered. The Q jet is a fantastic carb. If you dont want... it give it to me. LOL. The Q jet gets a bad rap from being misunderstood. They are actually about as simple as a stone axe.
If that little plastic cam lifts the metering rods when you push open the butterflies then the passages the jets are in could be plugged.
Be sure your float level and fuel pressure is correct.If you have allready rebuilt it ,that may be the trouble.


http://www.google.co.nz/#hl=en&sclient= ... 66&bih=651

[prado_boon]

thanks for all your replies. I know exactly how these quaddies work, I've been studying them for a couple of years. I have the that book too. but after everything I try I still can't get good secondary acceleration.
I had a ton of parts too. best is 78 jets, 49pri rods and 42b secondary rods with a k hanger... New this new that, but still bogs! not many people know what they are talking about that's the problem!

so this leads me to believe I may have head issues!

[prado_boon]

hmmm it could be the fuel pursue..... it's just a Holden v8 mechanical pump.... you'd think it would be ok.

[NJV6]

We have a quadrabog in the jetboat, but we have kept it as at cruising speed the secondaries are not open so it remains a little more economical.... If you have the book then you'll have checked the simple things like the vacuum flaps at the top of the secondaries are not opening to far? With the boat it is easy to get a mate to control it manually to see what the issue is though.

We found unless it was under a high load the secondaries would not even open even on full throttle, when opened manually it would bog from too much fuel.

Some of them were an electronic version as well but I think that just controlled the primaries.

[Heath]

We have a quadrabog in the jetboat, but we have kept it as at cruising speed the secondaries are not open so it remains a little more economical.... If you have the book then you'll have checked the simple things like the vacuum flaps at the top of the secondaries are not opening to far? With the boat it is easy to get a mate to control it manually to see what the issue is though.

We found unless it was under a high load the secondaries would not even open even on full throttle, when opened manually it would bog from too much fuel.

Some of them were an electronic version as well but I think that just controlled the primaries.

The idea of vacuum secondaries rings a bell too. If I recall the secondaries wont open until the air flow is high enough and forcing them open will cause it to bog - but I'm going from a half remembered conversation so I could be wrong.

[NJV6]

Thats right, the actual throttle blades open on the throttle linkage but the flaps you see on the video open by vacuum. As they open they lift the needles up letting fuel in.

[prado_boon]

Its an "on demand carb" the secondaries are HUGE and mechanically open but the secondary air valves won't open unless the engine demands it. Great design. They will out peform most carbs (hence how popular they are)...

Anyway, I think the carb I had on in the video had warped throttle shafts and probably a warped body. I just put another quaddy on and it seems much better. I'll have to test it out tonight.

I'm not spending $600 on a holley to get "average" performance "out of the box"... been there done that.

[Heath]

So what was the verdict?

[prado_boon]

So what was the verdict?

Got it running sweet, I have 5 quadrajets now!

Basically it was too lean, needed much larger jets which feed both primaries and secondaries. If anyone needs a hand tuning one give me a yell... I have heaps of parts!

[Heath]

Might have to take you up on that offer when the time comes to sort mine. I need to collect more carbs (only have 3 ), but I'd settle for one running one.

[Big]

Just6 make sure it's jetted correctly to the engine.. as I had a holden 253 ages ago..( over 20 years ago now.. ) and it was jetted for a 350 and what a pig it was.. changed jets and was awesome.. revved its arse off..lol

[Dannz71]

Gday. I dont mean to hijack threads but ive got a 350 chev with a few basic mods (4wd torque cam, Bit higher compression etc) nothing extreme. But im having carb issues with the holley 600 that I have on it. Im thinking about changing to a qjet. Cause ive Got access to 2 of them. Not sure the condition of them as they were pulled off years ago. Just wanted to know what size jets anyone with a 350 chev would recommend to start with before I take it in to get dyno tuned
Any input would b helpful

[Heath]

Do a search for cliff ruggles online and go to his website forum, join up and put all the engine info on there in a question about what setup would be best and cliff will be able to help you out. He's the qjet guru.

[prado_boon]

You sure it's a problem with the carb? Do you have an electronic dissy?

I've had a bit to do with holleys and quaddies. Pm me if you need some help.

[Dannz71]

Cheers for the help ill definitely look into it and get onto cliff and see if he can shed some light. Also how different is the bolt pattern between a standard 4bbl holley and a 4bbl qjet. Should be the same aye?

[derk]

Also how different is the bolt pattern between a standard 4bbl holley and a 4bbl qjet. Should be the same aye?

squarebore to spreadbore adaptors are pretty cheap and easy to fit

[Heath]

I'm guessing that if the qjets have been sitting for a while they will need rebuilding as the gaskets will have perished and probably the pump diaphragm will be toast. Depending on the manifold you may need a square to spread adapter (you may be lucky and already have a spread bore manifold under the holley).