Is it possible that GM made some QJ's with extremely large primary air bleeds

[bcwrench]

Hello,

1st post for me. I have a customer who swears this carb was working but I have my doubts and need to know if someone can shed some light on it.

Carb is 17085586. It has a reman tag on it (Autoline C-9526), Canadian re-builder and I am in Canada. Car is an 84 El Camino, originally had a 5.0L with a CCC Qjet on it. Owner decided to drop a crate 350 in it (stock cam). The dealership who did the install decided that they would drop a conventional carb on it and a knockoff red cap distributor. There's lots more but I won't bore you with it other than the fact it just won't stay running for me to hang my test equipment on it.

Primary calibration is in the normal area, 72 jet & 43K rod.

I can keep it somewhat alive by adding propane . The customer swears it purred like a kitten when he first got the car back.

On disassembly and preparing for mapping & recording the sizing and calibration of the innards, I came upon issues that alarmed me somewhat. I don't have recorded or available data on this carb series.

Of all the issues, the one that concerns me the most is the total sizing of the primary main air bleeds. It has two air bleeds on each side, one in the air horn and the other at the main well turn to the nozzle. Neither of these bleeds has any sort of brass calibrator in it.

Both of the orifices measure 0.120". This combination gives a total area of 0.02261952 square inches. This is equivalent to a 0.170 diameter hole. The main well measures 0.200"

I can't believe that any fuel at all could even begin to flow from the nozzle unless it was running at RPM that a stock rebuild could survive.

One other issue is that the air bleed tubes for the secondaries are not the same. One tube is shorter than the other by the length of the restriction tip on the lower end.

The end of the tube with the restriction has a flattened appearance just as if someone had tapped on it rather use the tool to install it. The orifice size is 0.026".

The shorter tube size is 0.051, which is the major diameter of most of the secondary tubes for Qjets. Both tube major ID's are the same. All measurement are down with pin gauges.

Any thoughts or has anyone run up against this type of calibration? I'm leaning toward hanging another carb on it as I have done the restrictor thing in the past and people just don't want to pay for it.

TIA

Scooty-T

[Kenth]

To answer your main question, yes, most if not all 1970 and later Chevy Passenger Car Q-jets uses .120" main airbleeds in airhorn and float bowl. Jetting varies a lot depending on application, but i would not use anything less than #77-#79 main jets with corresponding 48-49 primary rods.
For the current jetting in your carb i would install main air bleed inserts of about .070".

Your carb however, is a factory rebuilt unit (frankencarb) and as such the whole calibration may (will) be hacked up and needs to be checked and corrected all the way from the idle circuit thru the main circuit and WOT circuit.
I have not seen one (1) Qjet in at least 30 years with a "factory rebuild tag" on it beeing properly set up. On occation some have the correct matching airhorn, main body and throttle plate, but most are cobbled together with random parts from the degreaser.

Since the engine wont keep running at idle/low speed this is were you need to start, to get the idle circuit properly adjusted. Then verify the recipe for the rest of the calibration, at least to get close to a factory setup for a similar engine.

It can be done, but be prepaired to spend some time sorting this thing out.

[Cliff Ruggles]

I do this for a living and do NOT work on commercially "remanufactured" carburetors, lessons in humility await those that venture in that direction more times than not.

They do things to them unseen by the average "builder" plus the parts miss-matching throws a monkey wrench into things even further.

Oh, don't get me wrong, you can probably get it to work OK, but if you find an unmolested original carb it's just "plug and play" once you contact me for a rebuild kit with tuning parts to set it up for what you are doing........Cliff

[bcwrench]

Cliff,

No truer words could be spoken.

And all is fine if I could make it work, but is the customer going to pay? They just wanted the carb rebuilt, that should be easy according to all their friends.

Being that this is a hacked together engine replacement scenario, I feel it is probably best to slap it back together and walk away. Live and learn.

At 71 I shouldn't be doing this stuff anyway.

[bcwrench]

To answer your main question, yes, most if not all 1970 and later Chevy Passenger Car Q-jets uses .120" main airbleeds in airhorn and float bowl.

It can be done, but be prepaired to spend some time sorting this thing out.

Kenth,

Thanx for the info. I think this is one to walk the other way on.

It's hard enough to get 3 "B" series Rochesters on a 250 working in simultaneous mode but at least I am having fun doin it.


Tom

[Cliff Ruggles]

They just wanted the carb rebuilt, that should be easy according to all their friends.

Tell their friends to take a stab at it, and make sure that they keep their day jobs because they are going to get their asses handed to them trying to rebuild a commercially "remanufactured" carburetor and get it working correctly in all areas. 

I make a living out of sorting out issues with completely "rebuilt" and "restored" carburetors from every single source out there.  For the last 10 years of so I've opened up a couple of Saturdays a month to having folks bring entire vehicles here to get the engines tuned and running correctly.

By the time they get here all of the owners friends, beer drinking buddies, local shops, local "guru's" and even their next door neighbor has had a crack at fixing it.

It's ALWAYS the same thing, crappy parts, lack of attention to detail, and 9 times out of 10 someone put one of those POS spring/weight kits into the distributor and unhooked the vacuum advance.

You should see the looks I get when I "gut" the distributor and throw all that chit out before even doing anything with the carburetors, which is what they think is wrong in the first place.

Anyhow, large main airbleed carbs are really lean on the primary side right to start with.  The companies that "remanufacture" those carbs often drill the lower idle airbleed out even larger, then install a HUGE idle tube (for reasons I'll never understand), then the wrong jets/metering rods and at the same time they drive lead plugs into the idle bypass air holes.  To date I haven't seen a single one that didn't have the power piston hanger arms bent all over the place and the metering rods not even in the jets.

NONE of those moves will yield a good end result on 95 percent of the engines they get bolted to and the 5 percent that do run are just OK and not nearly as close as they should be........FWIW......Cliff