: Qudrajet: easy to rebuild?
10-11-04, 06:24 PM
Since I am going to be changing the intake manifold on my 425 in the near future, I figured I may as well do a rebuild on the carb... it does need it... not bad, but it could use it...
... how difficult is it? I never rebuilt a carb before, but I have a very good mechanical understanding, and I know how a carb. works... is it something i could set a few hours aside and do myself with normal tools... or is it more invlved then that? it would just be a regular rebuild, nothing speical or high perofrmance... I won't be changing the jets either...
Q-jets are a little tricky with mechanical secondary lockout when the choke is not fully open, but that is the only remarkable thing I can remember (I've been driving FI too long).
As this will be your first carb. rebuild, you might beg, borrow, or steal a digital camera and take lots of pictures of linkages before you undo any screws.
A Service Manual (or Q-jet rebuild kit) will supply the correct choke unloader set points. And I am remembering the accelerator pump linkage deserves careful adjustment.
Take your time and pay attention to details; this is not your basic carb. You can do it......
10-11-04, 08:28 PM
There is a LOT of crap inside there. Make damn sure you keep everything in order.
10-11-04, 08:48 PM
yeah a camera would be a great idea and shop manuals are good too what can really help is a good place to do it. i have a desk in my bedroom devoted only to rebuilding carbs adn by having all the space you could need and a good light that really helps a lot. Q-jets really aren't that bad to rebuild. just the choke linkages and stuff like that can get a little tricky. And i don't know if you know about it but while you have the carb apart you should put some epoxy on the bottom of the wells so they don't leak which is a common problem with the Q-jets
10-11-04, 11:37 PM
after reading this... I feel a whole bunch worse about doing it.... seems almost more involved then timeserrting my NorthStar :)
Here are why I think it may need to be rebuilt...
.... when the enigne is cold... and only when the enigne is cold, there is a dead spot about 1/2 throttle... she won't cut out all the way, but she'll sputter alot... if the engine is really cold, adn I try to keep accelerating at that point, it'll back fire, then sometimes stall out....
... until the engine fully warms up, even after the thermostat opens, if I floor it, it'll sputter and shake the whole car and not gain any RPM... after about 4 seconds of that, it'll either back fire, or start coming up in RPM... I think it has something to do with the secondaries? but... if the enigne has been running and is at normal temp... I can floor it at any speed, adn without delay she'll downshift and open the secondaries and take off....
my mothers '89 Brougham, also with the Q-Jet had a similar problem... but ANY time you floored it, no matter what temp the engine was at, it would sputter and not pick up RPM... at first for about 6 seconds, then finally it never did.. she ended up getting the carb rebuilt at a place.. still it was like $400 or so... I am not spending that to get mine rebuilt...
So I don't know if it is really the carb (what else would it be?) and if it is... maybe it is an external part of the carb? other then that problem it runs great, since I drained the cat of the catyalist beands, there is no more rotten egg smell form the exhaust, and there is alot more power... but tonight I took her out for a wuick spin to show my friend, and only after it was fully warmed up... after about 6-8 minutes, woudl it run wide open and not sputter...
10-12-04, 12:27 PM
I had almost no experience with carbs at all when I rebuilt my quadrajet. I found out though that it wasn't that hard. the kit I got from Napa auto parts had to be modified a bit and I didn't use some stuff like the three rod things that come in the kit. I couldn't for the life of me figure out what those did. It really helps hesitation to get a new accelerator pump though. I got my carb tuned by a mechanic so that the hesitation was almost un-noticable, but it still occured when the engine was cold. Never had any backfire problems. It turned out that my accelerator pump seal was completely ripped. The kit I got needed a little changing on one of the gaskets. The hole for the accelerator pump was very small(the size of the rod) so it wasn't coming far enough up. I used the spring holder to make a circle that I cut out. Its a little hard to remember to get all the linkages connected correctly before putting on the top of the carb. I used brake cleaner as opposed to carb cleaner because it evaporated completely and gets the components far cleaner. I didnt use pictures, but that is a very good Idea. The choke linkage is very tricky. I had a second carb to refer back to which helped a bunch in the reassembly.
10-12-04, 01:59 PM
yeah i don't mean to discourage. just trying to give some helpful hints. it really isn't much more thatn replace all the parts that come in the rebuild kit with new ones. and clean the parts while you have it all a apart. i used a combo of carb cleaner and mineral spirits and i let the parts soke over night then the next day i cleaned tem all off with a rag an old tooth brush and used compressed air to dry them off. but remeber if ther are any plastic/rubber parts you need to save probablly not a good idea to let them sit in any sort of solvent for very long. i also nkow that there are adjustments you can do to the accel pump to make it draw in more fuel thus pumping more fuel out too. i think Hot Rod had or one of those mags had an article on how to rebuild a q-jet. the manual that i bought that really helped i think was a Chilton's manual it has good descriptions and pic to describe what is going on.
oh yeah if you have some extra parts that you can't figure out where they go and you didn't have any parts like it the extra parts may be for a diff model of Q-jet. the early ones before the 70's were a lot more simple but the later ones ahve a lot of extra stuff on them to make the engine burn cleaner
10-12-04, 05:08 PM
hmm, I heard the accelerator pump may be bad...
... if the carb was to be rebuilt, would that give me a noticable increase in power or millage? I don't remember with my mothers car... the 307 never has power....
I remember reading that artical in HPP... maybe I should try to find one... they siad something about there being a little tab that prevented the secondaries form opening allt he way, that can then be filed down?anyone know about that?
it seems like I *could* do this, but i don't think I should mess with it at this time... especally since it is going to be winter soon...maybe next year, atleast the car runs and drives fine right now...
10-12-04, 06:40 PM
yes rebuilding will give a very noticeable increase in power.
either way, set aside not one hour or two hours, but a good 4 or 5... since it's your first time you'll probably need it. also remember where everything goes.
10-12-04, 09:39 PM
That cold running problem is probably a choke adjustment Wolf, the colder it gets the more you will notice it. I'm thinking that bog is the little spring that slows the opening of the secondary air doors. There is a little screw on the pass. side of the carb and a tiny allen under it that locks it. Take a mirror and look under the tab where the air door pivots, you'll see it.
10-12-04, 10:53 PM
Does my '79 have manual or electirc choke? I ask becuase I remember seeing a Q-jet on an 80's Monte Carlo with an electric choke, and the wires that go to it... mine has the same wires in the same spot...
... if it is that case, maybe I could disable the choke and see what happens... if it is a problem with the chome, is there a way I could fix it without tearing up the carb? or should I just live with it? it really isn't a bother as I never race a cold engine... but I was thinking that if there is a problem when it is cold, that it isn't running 100% efficent when warmed up... although if it is a choke problem, that may not be true...
the car does have 86k miles on it... so if anything is wrong witht he carbm it would be from age and sitting, not from too much use...
yours'll be electric...I built the one on my '72 472 eldo, 'twas my first carb build and it wasn't all that bad...I bought a quadrajet book from ebay and just took my time and made sure everything was back where it belonged. Took me about three hours. Buy a can of carb cleaner, do it away from flame or a heating element on a shop heater (almost had a catastrophy with this, until I realized the heater was on) and DON'T BREAK THE BUTTERFLY SCREWS. That's what set me back...luckily I had a spare...come to think of it, I still have it laying around somewhere in the garage...let me know if you need any parts from it. It'll be full of crap and gunk all over inside, probably, since its a bit older of a car...you'll definately get better mileage and better power all thorughout the rpms with a well tuned carb. Good luck with the rebuild!
10-14-04, 12:55 AM
As far as the choke goes it could be your problem. Unscrew the three bolts enough to let the cover moove around a bit. If you rotate it clockwise and the primary flap doesnt open or become very loose then the coil inside the choke isnt hitting the tab. If so remove the cover and make it so the coil sits behind the tab(so if you rotate it counter clockwise the primary flap closes tighter and tighter). There should be a little mark on the cover, just a straight line on the edge. Also there should be little dots on the metal part of the choke. Move the line counter-clockwise so it lines up with the dot two way from the center large dot( ...o... ) <---second from the left. This means its running two ritch instead of neutral or lean. That is the way the factory meant it to be. See if that works. Good luck wolf.
10-14-04, 04:38 PM
If you're going to go ahead and rebuild the carb, the best source of information I've seen is Doug Roe's excellent Rochester book. It covers everything about Quadrajets, including performance modifications, and it's inexpensive at a place like amazon.com. Also, keep in mind that some Quadrajet kits do not include an accelerator pump plunger or the float. If you decide to do the carb, get these two items, the rebuild kit, and a new fuel filter (no matter how new yours is). The Quadrajet is a pretty straightforward carb to redo as long as you take your time. If you drive the car regularly, it may be easier for you to find a spare carb in the local boneyard or on eBay (I see Quadrajets on eBay for as little as $30-$40) and rebuild it at your own pace rather than to rip your current one off the car and start tweaking. If you get into a jam, I'm sure someone here will be willing to provide some insight.