I have aquired 3 quadrajets. all three are slightly different. I plan on instaling one on a 350.

my question to all you "QJ guys" is,.....if I where to rebuild and install one of these three, wich one would be my best bet?

the number on the carbs are as follows.......

(1) 07029207 1511
(2) 7044502 3373 bm
(3) 7045506 0705 ty

Thanks <IMG SRC="smilies/beer.gif" border="0">

[ 09-28-2001: Message edited by: fc187 ]

find a guy on this board, goes by the lloyd. He seems to no more about Q-jets than anyone else, and I've been rebuilding them for at least 8 years...... <IMG SRC="smilies/glasses.gif" border="0"> <IMG SRC="smilies/glasses.gif" border="0"> <IMG SRC="smilies/glasses.gif" border="0">

I don't know the applications of those, but, I always look for the simplest carb for my use...as few vac. ports as possible, no wires or other emission control voodoo sticking out of it, and I always pull the choke system off and go with a hand operated choke.

I beleive the best q-jets to use are off of pickups something to do with the jets or something,My father-in-law uses one and he loves it

I think (brain fart) the ones used on the pickups with the 400 sb were a 795 cfm and worked best, but don't know the number. But if you have to smog it, you'll need all the right hook ups.

Unfortunately I dont know the orig application of theses carbs either.

although the first one is by far the simplest of the three with the least vac ports.

luckily emision controll stuff isnt an issue (pre smog) <IMG SRC="smilies/biggrin.gif" border="0">

I'll try and dig up "lloyd" thanks for the info guys <IMG SRC="smilies/beer.gif" border="0">

GO here: http://www.freivald.org/~padgett/roch.htm

Originally posted by Old Scout:
<STRONG>GO here: http://www.freivald.org/~padgett/roch.htm</STRONG>


dude, you rock!

btw, what happened to the smily face?
<IMG SRC="smilies/beer.gif" border="0">

Originally posted by fc187:
<STRONG>
dude, you rock!

btw, what happened to the smily face?
<IMG SRC="smilies/beer.gif" border="0"></STRONG>

I will bring him back after halloween. <IMG SRC="smilies/biggrin.gif" border="0"> <IMG SRC="smilies/usa.gif" border="0"> <IMG SRC="smilies/rasta.gif" border="0">

All of the Q-jets you mantioned were used on the 350 at one time or another. The First one you list(7039207) was used from 1969 to 1971 on 350 chevrolet engines and probably has the fewest emission parts and the idle screws should be open and accessable. The second one you list was used from 1973 to 1978 on 350-400-454 chevrolet engines idle screws are most likely covered unless some one has opened them up. The third one listed was used from 1975 to 1979 also on the 350-400-454 and will have the most emissions stuff as well as having the idle screws hidden.
As far as which one to use you will have to make that choice based on the condition of each carb and what it will take to get them in running condition. Any that have been sitting out in the weather or full of water would be low on the list,however , if they are all ready to run I would use 7029207.

Thanks Russ! "QJ GURU" <IMG SRC="smilies/biggrin.gif" border="0">

they are all in comparable shape (good),but
I actually was leaning towards the 702 for the sake of simplicity.

so 702 it is <IMG SRC="smilies/bounce.gif" border="0">

[ 09-29-2001: Message edited by: fc187 ]

I would go with the earlier year QJ. BEfore you tear into in check the throttle shaft bushings for wear, and also check the needle screws. Some folks are heavy handed when adjusting mixture screws and tend to over tighten them. This messes up the needle screws and in worse case, over enlarges the ports.

FC, my neighbor is a Chevy hotrod guru. He's like the best Quadrajet rebuilder in the whole world!
If you can't find this Loyd guy, give me a call.

Well I'm going to go against the grain. Go for the newer high emmisions version and here is why.
If it's new enough it has the hot air style choke. Those are esily converted to Electric choke. It will work on any spread bore intake. The older version will be the stove style and you might have an issue with your intake.
I own 2 GM trucks. one is a 75 with the older style no emmision quad and I own a 79. Pretty well run them on the same trails but I have more issues with the 75. Get the nose up highenough and it dies. NEVER had that problem with the newer version. I did a lot of compairing the two models and have come to the conclusion my problem is because of the float bowl shape. The primary jets on Quads are at the very front of the bowl. When you get the nose up they run dry because all the fuel slloshes to the back of the bowl on the 75. Their is a domed area in the top casting where there is a riser for the vent. The fuel doesnt dump out but it gives a lot more room for the fuel nose up. The Newer version with the vapor recovery bowl has less of a dome so less space for the fuel to slosh back so less chance of the main jets running dry. You do have to run a fuel bowl vent. If you graba air cleaner off a truck with a air pump there is a line on the clean air side of the filter that is perfect for the job. It comes out right above the vent on the carb and with a peice of 8 inch long 3/8 hose it will hook right up. Just block the timmed prots you dont need. looking at the front of the carb the port on the bottom right is your distributor advance. the rest you can block. on the side next to the choke bowl is a main vac for the Thermac on the air cleaner.

Originally posted by Grim Reaper:
<STRONG>Well I'm going to go against the grain. Go for the newer high emmisions version and here is why.
If it's new enough it has the hot air style choke. Those are esily converted to Electric choke. It will work on any spread bore intake. The older version will be the stove style and you might have an issue with your intake.
I own 2 GM trucks. one is a 75 with the older style no emmision quad and I own a 79. Pretty well run them on the same trails but I have more issues with the 75. Get the nose up highenough and it dies. NEVER had that problem with the newer version. I did a lot of compairing the two models and have come to the conclusion my problem is because of the float bowl shape. The primary jets on Quads are at the very front of the bowl. When you get the nose up they run dry because all the fuel slloshes to the back of the bowl on the 75. Their is a domed area in the top casting where there is a riser for the vent. The fuel doesnt dump out but it gives a lot more room for the fuel nose up. The Newer version with the vapor recovery bowl has less of a dome so less space for the fuel to slosh back so less chance of the main jets running dry. You do have to run a fuel bowl vent. If you graba air cleaner off a truck with a air pump there is a line on the clean air side of the filter that is perfect for the job. It comes out right above the vent on the carb and with a peice of 8 inch long 3/8 hose it will hook right up. Just block the timmed prots you dont need. looking at the front of the carb the port on the bottom right is your distributor advance. the rest you can block. on the side next to the choke bowl is a main vac for the Thermac on the air cleaner.</STRONG>

VERY intresting. definately something to take into consideration. I will pop the tops and compare them. If one of the newer ones have the bowls you are talking about, I may go that route. I would like to keep it simple as possible but it would sacrefice trail proformance, its just not worth it.

OK now the newer 704 is back on top the list <IMG SRC="smilies/biggrin.gif" border="0">

Thanks GR <IMG SRC="smilies/beer.gif" border="0">

whatcha think Lloyd? <IMG SRC="smilies/biggrin.gif" border="0"> <IMG SRC="smilies/beer.gif" border="0">

Sorry guys, I've been on travel for a couple of weeks.

There's been a lot of good points made here, only a couple of things to add. With the older ones, you can get rid of most of the void in the vent tube area with a piece of an old foam float; just trim to fit and stuff it in, maybe with a little RTV - not too much because you may want to take it out later. If you really feel creative you could use this to put a baffle in the vent tube area like the Holley "slosh kits" have; it's a little redundant in a qjet but doesn't hurt. Be careful to cut a big enough pocket in the foam for the metering rods and hanger - you don't want these to get hung up. Float shape can make a big difference also; they made a couple dozen different floats and some are better than others for offroad since they fill the bowl better - and thus control slosh better. You can get pictures of many of them at http://www.quadrajet.com, but you need to try to match the float shape to the contours of your specific float bowl, so a float that's great in one carb may not be best in another one. Another case where bigger is generally better. I've heard of people sticking pieces of old cut-up foam floats onto one to build it up, and then sealing it with epoxy or polyurethane, but I've never heard that these hold up well. Foam floats bounce less than brass, cheaper too, so I use those.

Don't have my books here, but I think either of the last two carbs you list could possibly have a functional aneroid, which was designed to compensate for altitude; only used in '75. I've never had one so can't comment much, but have heard that they didn't work so well. If anyone else has used one of these I'd like to hear about it. There's a method for disabling the APT system in Doug Roe's book, but it's actually a useful system for a wheeling rig because it allows you to keep the mixture leaner at part throttle (ie crawling type conditions) so fuel slosh and vapor enrichment (due to altitude and heat) will hurt you less. If you're builing a mud-monster, you may want to block it and consider more extensive mods like reaming the secondary fuel delivery passages (NOT the fixed sec. jets) etc. that are usually saved for race carbs.

Be sure to check shaft play on the primaries; this could be the deciding factor for me. I posted a proceedure for bushing these a while back; can't find it now. If one is much tighter here than the others, use it.

If they're all loose - which is likely the case - and you want to install bushings, here's how. K&S Engineering (out of Chicago) makes brass tubing that you can usually find in hobby shops and hardware stores. Buy a foot of this in 11/32" OD and 5/16" ID. Also buy some green loctite sleeve retainer. Remove the throttle plate assembly from the bottom of the carb, and disconnect the choke linkage. Now remove the throttle plates from the shaft; the screws are staked, so use penetrating oil, go back and forth a lot, and don't twist the little buggers off. Slide out the throttle shaft, and open the holes in the outboard sections up to 11/32" through. Conveniently the holes are this size for most of their length, but the shaft bears on a little raised bearing section at the end, and this wears pretty fast. I prefer a straight-fluted chucking reamer for this job, but a regular twist drill will work fine too. Cut and deburr two pieces of your tubing for those two outboard sections of the throttle body assembly, and press them in with the green loctite - they should feel snug, and be recessed a little from the throttle bores. If you want to thin and feather the primary shaft, this is the time to do it, but completely unnecessary unless you're trying to get 1100 cfm through it (which has been done btw). Put the throttle shaft back in with some moly/graphite grease and add the throttle plates. Be careful about aligning these correctly in the bores. Put the screws back in, and stake them down securely. Think about where they'll go if they come out <IMG SRC="smilies/eek.gif" border="0"> and stake them down securely again. One of the main advantages to this method is that the throttle shaft now bears on nearly 1" of brass at each end instead of 0.1" of soft aluminum, so one fixed this way should still be tight when you give it to your grandkids.

Also think about getting an Edelbrock kit for the one you decide to use - Summit has these for ca. $100. Be sure to get the right one for the carb you want to use since the primary rods for 070xxxxx series carbs don't interchange with those for 170xxxxx series carbs. Here's a link to the method of tuning a Q-jet that I prefer: http://www.pirate4x4.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic&f=11&t=000795

One other thing you might want to consider is to take the two last ones you listed, fix them up and get the Edelbrock strip kit (since these two use the same primary rods) and set up one carb for low elevation and the other for high. This way when you're done you can go play in the sand with perfect jetting for your engine/cam/etc. at sea level, and with 5 minutes work be set up perfectly for 12,000 ft. on the 'con just by swapping carbs. There are some nifty injection-molded carb cases to carry your spare in too.

Sweet! Good info on rebushing the throttle shafts! Thanks! <IMG SRC="smilies/skull.gif" border="0">

If anyone does decide to try adding bushings to the throttle shaft, be warned that it is very difficult to remove the screws that hold the butterflies to the throttle shaft unless you completely grind off the exposed part of the screw on the back side of the shaft. These are 3-48 screws, and they are VERY EASY to break. I take a die grinder and grind all of the exposed screw off - right down to the surface of the shaft. If you break a screw off (reminder - they break REALLY EASY - did I say that?), the throttle shaft will be scrap. Also, you can buy 5 1/6" ID X 3/8" OD sintered bronze bushings through Detroit Ball Bearing or the like. These work very well if you have trouble finding the tubing described above. The 3-48 screws can be a little hard to find, and if you grind them you will have to replace them in order to be able to stake them properly. A good hardware store will stock some screws this small, as will specialty fastener distributors.

Originally posted by Lloyd:
<STRONG>Sorry guys, I've been on travel for a couple of weeks.

There's been a lot of good points made here, only a couple of things to add. With the older ones, you can get rid of most of the void in the vent tube area with a piece of an old foam float; just trim to fit and stuff it in, maybe with a little RTV - not too much because you may want to take it out later. If you really feel creative you could use this to put a baffle in the vent tube area like the Holley "slosh kits" have; it's a little redundant in a qjet but doesn't hurt. Be careful to cut a big enough pocket in the foam for the metering rods and hanger - you don't want these to get hung up. Float shape can make a big difference also; they made a couple dozen different floats and some are better than others for offroad since they fill the bowl better - and thus control slosh better. You can get pictures of many of them at http://www.quadrajet.com, but you need to try to match the float shape to the contours of your specific float bowl, so a float that's great in one carb may not be best in another one. Another case where bigger is generally better. I've heard of people sticking pieces of old cut-up foam floats onto one to build it up, and then sealing it with epoxy or polyurethane, but I've never heard that these hold up well. Foam floats bounce less than brass, cheaper too, so I use those.

Don't have my books here, but I think either of the last two carbs you list could possibly have a functional aneroid, which was designed to compensate for altitude; only used in '75. I've never had one so can't comment much, but have heard that they didn't work so well. If anyone else has used one of these I'd like to hear about it. There's a method for disabling the APT system in Doug Roe's book, but it's actually a useful system for a wheeling rig because it allows you to keep the mixture leaner at part throttle (ie crawling type conditions) so fuel slosh and vapor enrichment (due to altitude and heat) will hurt you less. If you're builing a mud-monster, you may want to block it and consider more extensive mods like reaming the secondary fuel delivery passages (NOT the fixed sec. jets) etc. that are usually saved for race carbs.

Be sure to check shaft play on the primaries; this could be the deciding factor for me. I posted a proceedure for bushing these a while back; can't find it now. If one is much tighter here than the others, use it.

If they're all loose - which is likely the case - and you want to install bushings, here's how. K&S Engineering (out of Chicago) makes brass tubing that you can usually find in hobby shops and hardware stores. Buy a foot of this in 11/32" OD and 5/16" ID. Also buy some green loctite sleeve retainer. Remove the throttle plate assembly from the bottom of the carb, and disconnect the choke linkage. Now remove the throttle plates from the shaft; the screws are staked, so use penetrating oil, go back and forth a lot, and don't twist the little buggers off. Slide out the throttle shaft, and open the holes in the outboard sections up to 11/32" through. Conveniently the holes are this size for most of their length, but the shaft bears on a little raised bearing section at the end, and this wears pretty fast. I prefer a straight-fluted chucking reamer for this job, but a regular twist drill will work fine too. Cut and deburr two pieces of your tubing for those two outboard sections of the throttle body assembly, and press them in with the green loctite - they should feel snug, and be recessed a little from the throttle bores. If you want to thin and feather the primary shaft, this is the time to do it, but completely unnecessary unless you're trying to get 1100 cfm through it (which has been done btw). Put the throttle shaft back in with some moly/graphite grease and add the throttle plates. Be careful about aligning these correctly in the bores. Put the screws back in, and stake them down securely. Think about where they'll go if they come out <IMG SRC="smilies/eek.gif" border="0"> and stake them down securely again. One of the main advantages to this method is that the throttle shaft now bears on nearly 1" of brass at each end instead of 0.1" of soft aluminum, so one fixed this way should still be tight when you give it to your grandkids.

Also think about getting an Edelbrock kit for the one you decide to use - Summit has these for ca. $100. Be sure to get the right one for the carb you want to use since the primary rods for 070xxxxx series carbs don't interchange with those for 170xxxxx series carbs. Here's a link to the method of tuning a Q-jet that I prefer: http://www.pirate4x4.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic&f=11&t=000795

One other thing you might want to consider is to take the two last ones you listed, fix them up and get the Edelbrock strip kit (since these two use the same primary rods) and set up one carb for low elevation and the other for high. This way when you're done you can go play in the sand with perfect jetting for your engine/cam/etc. at sea level, and with 5 minutes work be set up perfectly for 12,000 ft. on the 'con just by swapping carbs. There are some nifty injection-molded carb cases to carry your spare in too.</STRONG>

WOW! Great info!!!!!!!!!!!! Somebody that types more than me hehehe. I'm famous for the long detailed replies at www.coloradok5.com. (http://www.coloradok5.com.)
Cutting and pasting that informatoin and keeping it. Thanks.

outstanding info..

here is a question for you guru's.. i have an older style qjet.. 702something.. its on the jeep now.. i had it rebuilt about a year ago.. ran great till about a month or so ago.. and its been driving me nuts.. for i kept thinking it was a fuel delivery problem..
ok.. here it is..
when i drive the jeep.. on road or off.. for awhile.. 10 mins or longer.. and shut it off... any amount of time.. when i run it again.. it will die out on me after its under load.... like there is air in the fuel line..
for this reason i now have a completely new fuel system.. electric pump.. return line.. vent line everything.. i am running a manual choke..
to fix it... i can let the pump run a few minutes.. and it will fire up.. and run good again.. or if i somehow keep it running when it happens.. it seems as the air will pass thru.. and run fine after that..
i am pretty much a carb idiot.. but it does this like clockwork now..
i also have 2 other carbs for spares.. i will check the numbers on them tonight when i get home.. and am thinking of rebuilding one of them for it.. i have rebuilt some old one and two barrels.. the carter kind.. and i know this qjet is way more complicated..
any thoughts on my problems.. its really getting annoying..
thank you..

Originally posted by jeepgod:
<STRONG>outstanding info..

here is a question for you guru's.. i have an older style qjet.. 702something.. its on the jeep now.. i had it rebuilt about a year ago.. ran great till about a month or so ago.. and its been driving me nuts.. for i kept thinking it was a fuel delivery problem..
ok.. here it is..
when i drive the jeep.. on road or off.. for awhile.. 10 mins or longer.. and shut it off... any amount of time.. when i run it again.. it will die out on me after its under load.... like there is air in the fuel line..
for this reason i now have a completely new fuel system.. electric pump.. return line.. vent line everything.. i am running a manual choke..
to fix it... i can let the pump run a few minutes.. and it will fire up.. and run good again.. or if i somehow keep it running when it happens.. it seems as the air will pass thru.. and run fine after that..
i am pretty much a carb idiot.. but it does this like clockwork now..
i also have 2 other carbs for spares.. i will check the numbers on them tonight when i get home.. and am thinking of rebuilding one of them for it.. i have rebuilt some old one and two barrels.. the carter kind.. and i know this qjet is way more complicated..
any thoughts on my problems.. its really getting annoying..
thank you..</STRONG>
\How close is the lines to the exhuast? Could be vapor lock. Boiling the fuel in the line. Sounds like heat related to me.
Check the secondary flaps and make sure they are free. You can overtighten the bolts (both that hold the car together and to the intake) and warp the housing causing the flaps to hang.
I asume you checked the stupid stuff like the Fuel filter in the front of the carb right? Hanging linkages. Take some carb cleaner and wash it off if it's cruded up.
You running a EGR? Make sure it's clossing properly. Carbon can not only stick them closed it can stick them open and give you weird problems. Mostly at Idle but under load if the EGR is supose to be close and it's open it could suffocate the engine.

Originally posted by Grim Reaper:
<STRONG>How close is the lines to the exhuast? Could be vapor lock. Boiling the fuel in the line. Sounds like heat related to me. </STRONG>

Yeah, me too. Don't know what it's in, but can you try to get cold air to the fuel line? Also, get a box of spring-steel binder clips from a stationery store and put them all over the steel line; they'll act like cooling fins and dissipate heat. You could also try dumping a gallon of diesel into a tank of gas - knocks the vapor pressure WAAAY down and helps supress vapor lock. Doesn't do much for performance, but if it helps it proves the nature of the problem, and only costs a couple of bucks to try. They sure will give you funny looks at the gas station though.

Lloyd,........YOU ROCK!!!!!
appreciate the info a ton!

IOU A <IMG SRC="smilies/beer.gif" border="0"> <IMG SRC="smilies/biggrin.gif" border="0">

Don

Originally posted by Big Rich:
<STRONG>find a guy on this board, goes by the lloyd. He seems to no more about Q-jets than anyone else, and I've been rebuilding them for at least 8 years...... <IMG SRC="smilies/glasses.gif" border="0"> <IMG SRC="smilies/glasses.gif" border="0"> <IMG SRC="smilies/glasses.gif" border="0"></STRONG>

Damn BR,.... you werent shitten! <IMG SRC="smilies/eek.gif" border="0">

<IMG SRC="smilies/beer.gif" border="0">

ya. vapor lock was my first guess.. ran all new fuel line outside the frame.. nada.. still did it.. checked filters and all the stupid stuff..
if i keep it running it runs fine.. well not fine.. its running rich also.. cant lean it out.. you can screw the mixture screws all the way in.. and it doesnt do anything.. unlike before.. i am going to tear into this thing this weekend... so am trying to get some ideals.. i might try rebuilding one of my others first.. then.. after i get it done.. take this one off.. and rebuild it..
me.. and everyone around is scratching their heads on this one.. but its definetly in the carb.. i have eliminated everything else..
thanks guys.. ill keep ya updated...

Inside, on the pass. side front, there's a little bimetallic spring with a valve to a vacuum port. They're supposed to open when hot and scarf the float bowl vapor. It may be that it's not seating properly, maybe some stuff in it? You can try blocking that interior vacuum port with a piece of gasket material. Also, replace the float. Foam slowly soaks up fuel and they sink. I'm starting to suspect a combination of these two things...

[ 10-12-2001: Message edited by: Lloyd ]

You also could have leaky plugs in the bottom of the bowl. Common problem on Q-Jets, and it would explain your rich idle.