Outer Limits 4x4 Board

I have just got a new Rochester 4 barrell carb and Edelbrock Performer manifold on my 253 Red V8.

It is very rich

Is there anyway to lean it out a bit aside from rejetting ? (I'm not to keen to rejet as just paid $400 bucks for the carb)

It seems that it doesn't go much harder than the old manifold and 2 barrell carb

Thanks

have you tried adjusting the mix screws ?

planb wrote:have you tried adjusting the mix screws ?

I'm no mechanic, but as far as I'm aware the rochester has no external adjustments - could be wrong though

Shorty40,

Are you trying to get your beast ready?, I know a friend of yours that just bought a big block 1.6l zook thats itching to out run you

Megaman wrote:Shorty40,

Are you trying to get your beast ready?, I know a friend of yours that just bought a big block 1.6l zook thats itching to out run you

I think even with a dodgy carb and no front tailshaft I'll still have the advantage

By the way, I'll be with him when he picks it up

Mate,

the zuki has triple overhead wiperblades, lowered chrome door handles and a momo steering wheel.

You'll be no match.

Bring shorty40 with you and i'll have a look at your carby

See ya soon

Dan

here is a copy of a thread i posted on pirate a while back, hope it helps




Thread
planb

Location: Sydney Australia
Member #17970
Rochester tuning question

Hello all,

Ive got a quadrajet Rochester that has just had a re-build

My problem is the guys at the shop didnt hot tune it and after bolting it back up to my motor (chev350)

its running like a dog.

Im told the general rule of thumb is to tighten the adjustment screws all the way in, then back them off 6 turns and it should be roughly in the vacinity of a balanced mix.

Ive done this, and its still runs like a dog

anyone got any tips on these things ?




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05-28-2003 12:34 AM

Drunk Monkey
Newbie

Registered: Feb 2003
Location: Round Rock TX
Member #16895
Posts: 27

I run a Q and the screws in front are mainly for idel. You need to check a few things. Hold you had at idle over the primaries if the engines revs up you either have a vacuum leak or the mixture is too lean. You also want to check where your Vacuum is coming in to the carb for the Vacuun advance on the distributer. The last thing you want to do is start changing jets and rods in the carb, because if it is something else then you willl be fighting a growing problem. I put an O2 sensor on the exhaust to get a reading. These are just some of the problems I have had in the past that made it seem like the carb sucked.


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Round Rock Texas




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05-28-2003 06:18 AM

RockinWagin
Wheeler

Registered: Oct 2002
Location: Double Oak, Texas
Member #14366
Posts: 146 Re: Rochester tuning question


quote:
------------------------------------------------------------------------
Originally posted by planb
Hello all,

Ive got a quadrajet Rochester that has just had a re-build

My problem is the guys at the shop didnt hot tune it and after bolting it back up to my motor (chev350)

its running like a dog.

Im told the general rule of thumb is to tighten the adjustment screws all the way in, then back them off 6 turns and it should be roughly in the vacinity of a balanced mix.

Ive done this, and its still runs like a dog

anyone got any tips on these things ?
------------------------------------------------------------------------


1. If the quys who worked on it don't know how to tune it, do you trust the rebuild?

2. If you are fighting a vacuum leak, you will never get it set right. An old trick to check for a vacuum leak is to spray starting fluid around the carb base and vacuum hose connections. If the engine smooths out, there is a leak.

3. 6 full turns out--I don't think so. Try 2.5 turns out.




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05-28-2003 08:09 AM

Cruzilla
Wheeler

Registered: Feb 2002
Location: IDAHO
Member #9851
Posts: 188

One real easy way to tune a carb is to put a vacume gage on your intake manifold ( unrestricted source, ie: break booser port or auto trans vac port) adjust idle screws evenly out untill the needle is smooth (it will jump around at first) , keep adjusting out un till it gets rough again then screw back in just to the point where it gets smooth again then stop......presto your done!!
Of course this only works if you don't have any vacume leaks!

Good luck,

-Scott


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05-28-2003 08:21 AM

Zipp
Wheeler

Registered: Oct 2001
Location: Davis, CA
Member #7631
Posts: 280

2.5 turns. That's what I've heard/used.


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05-28-2003 09:58 AM

planb
Newbie

Registered: Mar 2003
Location: Sydney Australia
Member #17970
Posts: 2

Thanks guys, ill get the vacume guage out and tinker some more,




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05-28-2003 03:56 PM

kruzrtek
Wheeler

Registered: Mar 2003
Location: Springville, UT
Member #17477
Posts: 180 Setting idle mixture

The way we do it after a GOOD rebuild is to bring the mixture screws out about 4-5 turns. Then screw them in slowly one at a time until the engine starts to run a little rough, then back it out 2 to 2.5 turns. But since you are close to sea level, you'll want a slightly richer mixture, so I would go about 1.5 to 2 turns out from the rough spot. Also remember, that when you are adjusting the left side of the carb(U.S. passenger side) you are affecting the opposite bank on the engine. (If still equipped w/ stock dual plane intake manifold!) And again this is taking into consideration that the carb was set-up right to begin with. If they mix up or change the jets and metering rods so they aren't the ones that were together originally, you'll have a hell of a time trying to set it up!!! The rod size has to match the jet size and the individual rods and jets have their mate. If that is not right, well then, GOOD LUCK!!!!! Also see what type of weight you have verses the rods and jets. (Only some quadratoilets had metering weights).

Good luck again!!!
Richard
Kruzrtek
kruzrtk@xmission.com




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05-28-2003 10:19 PM

Eskimo
Rollin Nolen Wannabe

Registered: Mar 2002
Location: Near Raleigh, NC
Member #10429
Posts: 1406

The way I've tuned mine, as told to me by the resident PBB q-jet guru, is to set the idle, and adjust the mixture screws until you get the highest vacuum, then out 1/2 turn.. it will take about 5-10 minutes of fiddling.


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Blue - '73 FJ-40, SO/SR/101"WB & stuff.

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Thanks PlanB

How do I check if it has a vacuum leak, and will this be a problem with the carb or the distributor ????

im just starting to understand the stupid things, so dont hold me to it but,

if its a brand new carb then i would hope the vacume lines are all in good nick, and not corroded (as they will be over time), ive found most of my vacume leaks in the past have been because the gasget between the manifold and the carby is shot, or one of the four retaining/mounting bolts has worked its way loose and is allowing air in.

my guess is that your just running to rich, and that you dont have a vacume leak.

check where your mix screws are set, they should be around 2.5 turns out

if all else fails call the carburettor service co in burwood on parramatta rd, 9747 4066, they're helpful on the phone, and will tune it for you on the cheap.