ck76239

Hi guys, I got tired of messing with eproms and the crossfire in general, so this weekend I finished up putting I put an edelbrock perfomer manifold on my 350, a quadrajet that came from a 76 buick 350 ( I pulled it from the junkyard) and I put in a new cam in, its a comp cams XE-262H, and a vacuum advance distributor from the junkyard. I'm having trouble setting the intial advance though...

I set the distributor in, lined up with #1 on the cap, w/ motor at TDC, then
I fired it, and ran it between 2000 - 2500 rpm for about 20 minutes. Then I went to set my inital timing, and un-plugged the vaccum advance from the junkyard distributor. Motor was idling about 1100 rpm, I put the timing light on it, and the line on the balancer was off the timing tab, maybe about 20 degrees advanced. So I rotated the distributor, and the rpms dropped, as soon it it hits around 12 degrees advanced the motor will stall. I figure I should run it about 8 - 10 degrees advanced, but it just wont go down that low.

The carb is nice and clean, the buick had 60,000 miles on it, and I would rebuild it if I though it needed it, but it is really nice looking inside and out. Should I try messing with the idle mixture screws? What else can I do?

The motor is 9.8-1 CR and now I'm having troble starting it too, when it was cold it cranked fast, when the statrter was having trouble cranking it. Could it be from the timing being too far advanced, or is 9.8 too much for a stock starter?

(Cam Specs are as follows, Duration @ 0.006" 262 / 270, Duration @ 0.050" 218 / 224, Max Lift w/ 1.5RR 462 / .469, Lobe Separation 110, Intake Centerline 106)

Thanks!

99Hawk120

Okay, first stupid Q, you DID plug the vacuum line coming from the carb when you unhooked the vacuum advance, right? Otherwise you have a possible vacuum leak (depending on manifold vs ported and how far the throttle blades are open...

ck76239

Thanks for the reply, yes I did plug the vacuum line, but if it sounds like a vacuum problem I'll check the other lines to make sure I didn't knock something off...

Maybe I'll even get a vacuum gauge... Any idea how much vacuum the motor should pull with this cam? I know stock is usually 19 inHg, so maybe I'll have 16 or 17 inHg now???

Sonix

iTrader: (1)

yea, 16" sounds right-ish. kinda depends on altitude and whatnot.

that q-jet is probably going to be a total smog setup, you may want to check the rods/jets, but it'll be lean across the board stock. Hence it wants to be lean at idle, and you have to bump up timing to make up for it. That's actually not a bad thing, run more timing at idle makes the car run better. If you *wanted* less timing at idle, you'd have to open up your primary metering rods. More timing makes it harder to start. Also higher comp. If this is an old stock starter, it will have a shorter life. oh yea, definately post your primary rod/jet setup, and secondary rods, they're probably pretty tame, and you'll want to get better ones for that.

grab some timing tape, and set your timing at 3000RPM to 34*, then let it idle and check it. It'll be what it is, leave it at that. Ported vacuum is probably what you want for that motor. Manifold might give you an excessively high idle. Back your idle screw out until you have a 750RPM idle. Shut it down and remove your carb, and stick a feeler gauge in your primary throttle bores. you should have ~.040" gap at idle, if it's off, then you'll have an off idle flat spot. You should just be able to see ~1/2 the rectangular idle transition slot. So to tune the car well, you only get a little bit of use of that idle screw. (such that you stay in the .040" gap range) Other then that, use the mixture screws to get best vacuum, and set timing to give the idle speed you like. Then you can change springs to get your favorite curve. I'd recommend an msd 96001 timing can.
You may have to mod your q-jet for best perf, not hard, and worth the time since it sounds like you've put some effort into the engine.
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articles

if you want to go in depth, and tune up that q-jet to the max, then read the .doc files in this directory. The more you know about the carb, the easier it is to tune to your liking. This goes over some of the common things of setting up a q-jet, and modding it for a performance application. I don't think your setup is wild enough to need to drill the throttle plates, drill the mixture screw holes, etc etc.. oh yea, you should modify the secondary tang so you can get all 750CFM out of it though. and make sure your secondary air valve tension is set right.

ck76239

Thanks for your help Sonix, I did find a vaccum leak at the modulator on the th-350 tranny. Rubber line popped off.

Anyway, I fixed the vacuum leak and was able to get the timing down.

I've been reading through those articles, and I'm pretty certain that I'm going to get a rebuid kit for that q-jet.

Where can I get new rods/jets for a q-jet if I do need to go up/down a size?

Thanks!

Sonix

iTrader: (1)

u-pull junk yards are my favorite for q-jet parts. just make sure to stick with post '74 parts, since that's what your carb is, and some don't interchange there.
I just grab a carb from the carb bin, then dig through and snag all rods and jets. most smog engines have the same lame secondary setup though, so you have to hope to get lucky.
or get them from edelbrock. That's how i'm going to get some 76 primary jets, since i've never seen them that big at the wreckers.

ck76239

Thanks for another good idea... I remeber seeing some big caddy motors
(425,472,500's) over at the u-pull it... All were mid 70's and had quadrajets on them....

Ugly looking things those big caddy, wonder where they're all coming from, must have been five of them there....

Sonix

iTrader: (1)

yea, it's hard to say what vehicles would have good primary rods/jets, and good secondaries. Bigger engines would have bigger primaries i'd say, and high perf stuff (rare in the jy) would have good secondary stuff. best bet is to get very good at ripping up a q-jet to get to the primary rods/jets, and just keep tearing them open and checking. secondary rods are easy to nab.
maybe damon will come on here and give you a few hints, I think he might know a few vehicles to watch for. I found a lot of FAT useless secondary rods, like DD. I did find a few DR's, and some 74 jets and 43 rods, those are very common.