Gumby

Well short story is I got a Qjet and need to do some tuning. Everyone say get that book by Douh Roe [Rochester Carburetors by Doug Roe ]

So n e ways I bought the book but also looked around and found a NIB [Holley four barrel Rochester] for only $50 brand spankin new.

Well as some of you will already know there is a big difference in a Holley Rochester and a Rochester Qjet.

Though the Holley Rochester I got is a real replacement carb for the qjet. Has directions how to change it over.

The Holley Rochester is nice n new, all adjustments are easy to get at.
Full manual instead of vacuum. But will I be going backwards performance and tuning wise? I know its not a DP here but should I keep it or sell it?

Then find another Rochester Qjet like I have and with my Douh roe qjet book get where I was heading.

Kinda likea fork in the road here. Got that book and was ready to dive in and become a qjet tuning expert but I have this other direction I could go here???

Anyone have any tips???

Gumby

Now here is my carb, ignore the dirt, was rebuilt about 10,000 miles ago, just had it off, all nice inside, got orange crap all over it putting it back on. Was just a quick pic to double check my full manifold hookup. Haven't run it yet as I was waiting for my book n new carb



new carb

five7kid

iTrader: (14)

"Holley Rochester"? Never heard of such a thing.

I have heard of q-jets rebuilt by Holley. I've heard of q-jets made by Carter.

But I've never heard of a Holley Rochester.

five7kid

iTrader: (14)

Oops, started my reply before you posted pics.

That's a Holley spreadbore econo carb. Something like 450 CFM. Had one on the 396 when I got it, pretty doggy thing. Put it on a 350 pickup before I sold the truck.

I'd say forget it. Stick with a good ol' q-jet.

Gumby

Says on box
Standard replacement carb
Designed to restore original performance

tried to find out what the part number meant but could never find it.
CMF n such.... Made mistake n posted in tech when I asked week ago about the part number. Got some 900 page pdf list from a yahoo that wasn't even close to similar numbers.

2-3068

five7kid

iTrader: (14)

That is not a standard format Holley part number. See if there is a "List" number stamped on the carb itself.

It was a replacement carb for 60's and early-70's applications. It certainly is not a 3rd gen standard replacement. It's a little better than a leaky, cracked, warped early q-jet, but does not have the performance potential of a q-jet in good operating condition. If all you want is for the car to run and get you around, it will be fine. But, that's about all you should expect out of it.

Gumby

Well any chance you know of a place were you can buy rebuilt qjets with like the adjuster plugs removed n what not.


Guee I can't lose though. Carbs like the one I got For $50 are selling for $165 plus shipping on Ebay rebuilt.

Mine has all them extra needed parts to do the whole conversion right with directions. Should get $150 easy.

sofakingdom

iTrader: (1)

I agree. It was supposed to be an "econo" Q-Jet or FoMoCo or ThermoQuad replacement back in the early 80s. It's long since been discontinuesd. Those were truly a POS. Get rid of it. Sell it to the next "greater fool" you see coming.

Your Q-Jet is a non-computer-controlled one; looks like it's off of a Buick or Olds motor by the way the fuel line doesn't fit, maybe about a 78 or 79. Chevy fuel lines don't stick straight out the front like that, they go to the side.

What kind of a motor is this? About all I can tell is, it kind of looks like it's a small block Chevy. That foreign carb is hacked onto there pretty hilariously.

It's an emissions carb, of the most smogger kind there is. It's about guaranteed to be a pig.

If this is supposed to be some kind of a performance setup, but you want to retain good gas mileage and all that, get a Holley 6210. It's a spreadbore 650 CFM with manual secondaries and double pumps. Once you get out of the habit of stomping it to the floor at a stop, and learn how to roll into it (maybe you already know that, I wouldn't know), it's about the best running spreadbore carb there is. It will give roughly the same gas mileage on any given motor htat a well-tuned Q-Jet will, but a whole lot better power and throttle response.

I don't know what all this talk about "full manifold" is all about; that port you have pointed out is the ported vacuum for vacuum advance. If it has vacuum all the time, then something is dramatically wrong, such that the throttle blades are WAY too far open at idle; like, maybe there's no PCV valve? Hard to say.

Sonix

iTrader: (1)

A junkyard should have gobs of q-jets just piled in boxes. I just grab the dirtiest one I can find, then rebuild it to my liking. ~$25.

That carb looked like a square bore, but a WEENIE one. Like dual primaries sorta thing. I can see 450cfm out of it.

Apeiron

The bore spacing gives it away as a spreadbore, even though it has the weenie little secondaries. Most people are used to seeing the huge secondaries and thinking they're the definitive characteristic of spreadbores. On a Thermoquad you could almost lose your can of beer down the secondaries if you weren't careful.

Sonix

iTrader: (1)

I thought squarebore meant equal sized primaries and secondaries, and spreadbore meant unequal sized primary and secondary butterflies?

How can you tell with the bore spacing? ie, x inches means _____, y inches means...?

Apeiron

Squarebore carbs can still often have different sized primaries and secondaries, just not as extreme as the size differences that you'd find on most spreadbores.

I don't remember the actual differences in the primary bore spacing between the two, I'd have to look it up or measure.

five7kid

iTrader: (14)

This little piggy went to market as a q-jet replacement carb. It bolts down to the manifold just like a q-jet, therefore it is a "spreadbore" pattern, regardless of the size of the bores.

Sonix

iTrader: (1)

Well i'll be damned. Learn something new everyday.

Gumby

Well the full manifold vacuum thing is cause the guy I sent my dizzy off to rebuild said to use full manifold vacuum, not ported like stock #1.

Was using that pic to try and nail it down for good which one to use.

Some say use the lowest port on the carb which is #5 in this pic. But it says EGR though the EGR may run on full vacuum. Pic shows #3 as manifold vacuum but doesn't say full and its way up high.

Sonix

iTrader: (1)

Play around with full or ported vacuum for the dist, it depends on the motor, etc. I prefer to use ported, for various reasons. F-bird wrote a few posts singing the praises of it I think, if you want some reasoning on it, try to find those posts. Full is good for a fairly big cam, but it introduces all new problems so...
EGR? The tree huggers like you eh I don't know about that, mine is long gone.

Gumby

Well the dizzy was built/setup for full. He uses the crane adjustable but does some sort of pinned mod to it so they work right. Not sure what it is, not real hard.

I am using the EGR port right now [lowest posrt on carb body] and all is more then well.

No more off the line bog or Det. Just put it to the floor.
Before I couldn't get timing right, I could get off the line hard but it would det, I could bog but not det, went in circles forever on that.

Don't thin kI need to do anything to the carb now.
Cept maybe buy a new bigger one.

Dude on Ebay selling rebuilt version of that hollet 450cfm for $165 would take my NIB one on trade for the rebuilt DP he sells.
Send carb n $200, get a 800DP holley back.

Good deal for rebuilt? And the nice kind where it all re colored and fresh with warranty.