help me ID this q-jet

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clutchdust

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i'm looking at this (http://lasvegas.craigslist.org/pts/1009378130.html) craigslist ad and i'm just trying to determine what this q-jet might have come from. the info that i've found on-line doesn't show this type of q-jet on a 1980 z-28. i'll probably snag it anyway just because i hate that f-ing holley so much. i just want to know if i'm going to be 'potential restricted' with this q-jet over another.
thoughts?
 
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LInky no loady for me.....BUT....in general.....any Qj with the fuel lines going sideways to the pass side came off a Chebby or Caddy.....and straight ahead was BPO.....dunno about GMC.....

I have been told there were two basic sizes for Qjets, the 'smaller primary' variety rated at 750 cfm, and the larger rated at 800 cfm.....

the smaller ones had 'humps' in the barrels, so instead of being totally round, they had a dent in them seen easily by opening the choke, much less seeing through it with the throttle open......

This is the best information I have from a knowledgeable enough mechanic friend some years ago....I forget the source, It MAY have been even Brad Urban from Ontariio Carb Shop.....20? years ago.....
 
thanks GENE. i fixed the link. all the info i've found on line show pretty much the same carb for this year BUT with the fuel line going straight in like you say for BPO. the guy says it came off an '80 z-28 which jibes with the number he found on the side (17080204). i'm just surprised all the sites i've found so far show that BPO version.
i also have the doug roe book but much to my surprise it doesn't have squat in there about indentification.
 
It LOOKS like the one off my dad's '79 Caddy Sedan DeVille.....425 engine....problem is, it could be off a Camaro too, I have NO CLUE...sorry....

:bonkers::rain:
 
he must have deleted it since i picked it up. it looks pretty decent but there's a boatload of slop in the primary butterfly bushings. now i need to put some bushings in it and some gaskets and i should be good to go.
 
mrvette said:
big2bird said:
1980/49 state/Chev/Auto tranny............is what I get. As long as it's not a truck carb, I think you'll be okay.
http://www.recarbco.com/technical/rochester/qjet.html
Click to expand...

Uh, ok, dumb question....what is the diff between a truck carb and a car carb???

should work, assuming similar size engine...NO???

:chinese:
Click to expand...

Wrong throttle plate gasket
Results in: Poor idle, erratic idle, ineffective idle mixture screws, symptoms of a vacuum leak.
Comments: There are several different designs for the throttle plate gasket, and they do not interchange. Two common problems occur: The first problem was addressed in a GM Service Bulletin around 1971. There is a difference in the open area in the gaskets just forward of the centerline of the primary throttle holes. Some later carbs use a gasket with a larger open hole in this area. If this gasket is used on an earlier carb, you will end up with a massive, undetectable vacuum leak. The other problems with these gaskets occur due to the idle fuel and vacuum bleed holes not lining up from one design to the next. Use of the incorrect gasket can result in blocked idle fuel and blocked vacuum signals. Always lay the gasket onto the float bowl and onto the throttle plate to check the hole alignments.
Another odd twist to these gasket designs occurred in the late '80s. We are seeing more and more late '80s truck Q-Jets (non-ECM carbs) being used on musclecars, so the problems are becoming more frequent: In the late '80s, there is a fuel discharge hole drilled from the secondary fuel well to a small hole located between the secondary throttle holes in the base of the float bowl. Carbs with the fuel hole require use of a gasket that has NO HOLE at this location. If a standard late '70s or early '80s gasket is used with this carb, manifold vacuum will siphon fuel right out of the secondary side of the carb, discharging the fuel right out of the power brake vacuum hole location in the bottom of the carb throttle plate. You will have a massive rich-running condition, even with the idle screws completely closed (blocking all primary fuel flow) and with no evidence of fuel being discharged on the primary side.
 
Gene,
I just remember that Lars told me any car carb is good, stay away from Truck carbs. Ther ARE differences. I can find out more if you like.
 
big2bird said:
Gene,
I just remember that Lars told me any car carb is good, stay away from Truck carbs. Ther ARE differences. I can find out more if you like.
Click to expand...

NO, that's cool, my last Q is long gone, I had no recollection of the term 'truck carb' as to be related with that mani mounting gasket crap....I remember that shit now....always to double check that for just what you esplained up there....

Makes me wonder what in hell was the gain to be doing that crap with two different carb flanges/gaskets/patterns......to cure some very LO mid range torque thing?? I guess??

over the years the very BEST fix for any carb problems of any type was to put on a CARTER AFB, for even AVS, and run a CARTER electric pump back at the tank pushing forward......

cured EVERY damn running/idle/start problem I EVER seen on ANY engine....

usually picked up on economy/MPG too, unless it was a really great Qj on there.....

All I can post about is the experiences of me and my friends over the decades....

:shocking::beer:
 
well now that i own this thing, it looks like the biggest deal with it is the primary throttle shaft is sloppy as hell. anybody know a source for a rebuild? i wouldn't mind putting fresh bushings and even a new shaft in it. besides, this one is off an auto and mine is a stick. not sure what the differences are but if i can replace the shaft, might as well just get one with manual linkage instead.
in the meantime, can i put the lower throttle plate from my E4ME on this 4GC?
 
Carb number 17080204 is a 1980 Chevy passenger car carb. It can be set up to run very well on a Vette/performance application. Stock jetting is 72/42/CH (pri jet/pri rod/sec rod), and I'd bump the jetting to 74/42/CH if you're putting it on a performance engine with headers and good exhaust. Set float to .420" and make sure the power piston APT has the piston at the right height (see the "Quickie setup procedure" in my Q-Jet paper).

The difference between the passenger car carbs and the truck carbs lies in the booster venturi design. The truck carbs use a booster venturi that produces stronger fuel metering signal at low rpm (for lugging a horse trailer around at 2300 rpm). Due to this different booster design, the primary metering rods on the truck carbs have fatter tips (leaner) than the passenger car carbs: The passenger car carbs have .026" diameter tips on the primary rods, where the truck carbs have .036" diameter tips. Thus, you cannot interchange primary rods between trucks and cars in the 1975+ carbs. The passenger car carbs will perfrom better at high rpm than the truck carbs, which are intended for low rpm usage.

Q-Jets, when brand new, had pretty sloppy throttle shafts - this observation came up with the students at every Q-Jet class I taught at the GM Training Center. Unless the throttle plates are binding in the bores and causing the carb to not return to a consistent idle due to the blades cocking in the bores, there is little to gain by installing throttle shaft bushings. There are vacuum leaks all over a Q-Jet (down the power piston, through the hot air choke housing, etc), and they do not degrade its performance. Don't install bushings unless you have a return-to-idle problem with the carb.

Lars
 
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