84-Z28-Canada

Hi Guys,
So, i've built myself a mild 350 and swapped it into my car. I've got it running with the q-jet, and it actually doesn't run too badly. Here's my concern. When I had the 305 still in there, I would get up to about 100km/hr then try to accelerate and it would bog and cough a bit. I haven't gotten the opportunity to get out and do the same with the new motor, but I can't see the problem magically disappearing. I have the opportunity tomorrow to get a great deal on a new Edelbrock 1406 (600cfm, Elec choke), and i'm wondering if I should just make the swap. I know that q-jets make good power when tuned right, but on my combo ('78 350, 4 bolt mains, truck cam, heads w/ 1.94" intake valves, Weiand 8004 intake, Crane Cams 1.5" roller rockers, Flowtech 2.5" headers and y-pipe, 3" Magnaflow Converter, 3" Flowmaster Cat-back) would it be easier to make the same HP with the Edelbrock? I know the 1406 is the "Economy" version, but I only want to make about 350-375 horse anyway (for the moment). Love to hear your insight guys, thanks. Ian

five7kid

iTrader: (14)

Fix the q-jet. Going to the Edelbrock is only inviting problems, and it can't possibly make more power than the q-jet, assuming both are running as they should be.

This issue you had when it was still the 305, were you flooring it from 100 km/hr, or just trying to go faster than that?

84-Z28-Canada

Hi five-7, always good to see your advice. I've been hearing a little of the same from others on the board about the Edelbrock. Is this the same deal with Holleys and the like? I found a similar local deal on a 670cfm holley street avenger. Would this be inviting problems as well?
As for the problem on the 305, I would get up to about 100km/hr, then accelerate (say up to 120km/hr) and it would stutter and hesitate then eventually get there. I don't mind using the q-jet, but it is old and I doubt it's ever had the rods or jets changed. Is there a "first time carb tuner" approach to sorting out the potential issue? thanks very much - Ian

naf

iTrader: (7)

Stutter and hesitate sounds like it could be an ignition issue. Make sure all of that is top-notch before blaming the carb. If it's just bogging, check out the tech article here on adjusting the AV tension.

A replacement mechanical q-jet (if you need/want one) can be picked up reman from Summit or other places. It will fit your intake and likely better fit your wallet. Yours should be an export model without the electronic qjet?

84-Z28-Canada

yep, canadian carb with no computer. I have upgraded all of the ignition since it was on the 305, so I could already have my answer. I run a HEI distributor with an accel high voltage internal coil, followed by 8mm taylor wires and all new Delco spark plugs. I haven't gotten the chance to get the new combination up to speed yet, so I might be trying to solve a solved problem. Great to know about all of this in case I am getting into carb stuff. Would it not be easier to change the parts/rebuild the q-jet I have than to get a replacement q-jet? I've heard horror stories about rebuilding q-jets, but it will take more than a complicated piece of machinery to frighten me appreciate the responses guys

shinzon1

iTrader: (1)

I'd say there is a good chance that you may need to change the main jet size, most likely going to a larger size. I'm not very familiar with Q-jets, but that's where I'd probably start if everything else appears to be working properly. If you go with an Edelbrock go with the 1405. Its not tuned for "economy" and is a manual choke, but very easy to tune.

naf

iTrader: (7)

Rebuild is plenty easy. Plenty of walk thrus on the net for the mechanical ones. An afternoon and maybe $40-50 in parts and cleaner. Doug Roe's book can be interesting reading as well.

84-Z28-Canada

Thanks very much for the replies. I think if the problem persists with this carb/motor combo, I will rebuild the q-jet. I know guys are making good power with them, and besides, if I can't rebuild a carb I shouldnt be driving these cars, am i right? Now for the heads....458642s....they're alright for now, but from what I hear, they're better off as wheel chocks. thanks guys

Apeiron

642s are some of the better stock SBC heads ever made.

84-Z28-Canada

Wow, I'm really glad to hear that Apeiron. I wonder why i have been hearing such a different story from other posters on this site and on others. I'm glad to keep them on there, I haven't gotten any time slips yet, so who knows they could be great. So far they haven't done me any wrong. I'm interested to find out if the Holley Street Avenger would be a good choice for my car. Everything else considered, I think a little carb tuning could wake the car up a bit. I'm trying to find out with my combination what would be a good carb to tune some more power out of (even if that means sticking with the q-jet). Appreciate the responses all

84-Z28-Canada

Oh, and with the current set-up that I have, what kind of power should I even expect to be making?

Bob358

Don't ever give up on a Q-Jet. I also have a 1984 Camaro that I built a mild 350 for. Used the same original Q-Jet from the 305. and the computer readjusted the primaries for the 350. The check engine light even went out. I was amazed! I did tweak the secondary rods and hangars and adjusted the AV for the extra cubes. Seems like maybe your secondaries might be the problem, which are totally externally adjusted. Good luck!

84-Z28-Canada

Hi Bob, thanks for the reply. I've been wondering about that, because it would be the secondaries causing me trouble if I'm running at 100kph and then try to accelerate more. So, do you have a set of rods and hangers that you suggest using? Is there decent aftermarket support for upgrading the q-jet? thanks very much

Bob358

Hello again. I used Edelbrock rods PN1950 and hangers PN1960. Ordered them through Summit, but can be ordered from most auto parts stores. You can go to Thirdgen Tech Articles here and look at "Tuning for Performance with your Computer Controlled Quadrajet" Secondary tuning is the same for computer and non-computer Qjets. You can print the article.

Also, if you have a vacuum advance HEI, make sure the advance is working properly. My HEI is computer controlled...no vacuum advance. Good luck again.

paul_huryk

I did the same thing, a mild 350 swap - then I went for something more powerful and the carb was not even an issue.

It sounds like a fuel pressure problem, possibly an ignition one (both or just one). You want about 5psi of pressure under load with a q-jet and not much more at idle (or it will just shoot gas out everywhere).

ADV1

iTrader: (1)

Q-Jet > **

daveb123

"DR" rods with the stock hanger work great on mild 350s.

Willsmith305

Hi kinda late reply but I just put a 1405 (same thing but manual choke) on my 89' camaro and it took about 20-30 minutes to find the right tune with it. I switched from a Q-jet myself but there is nothing wrong with a Q-jet, mine was just getting a little too old. If you do end up switching to the 1406 you need to get a new kickdown cable bracket and possibly one for your throttle too.

Ozz1967

iTrader: (4)

Mild 350 here, running a slightly modified CCQjet, nary a problem once I nailed the tune down. Qjets don't like low vaccum though, gave me fits because it wouldn't pull enough fuel on the idle circuit which is when I sent it off to have it modified a bit (I'm running 15hg vaccum at idle). As long as you keep it in the high-teens and 20's off idle you should be fine.

84-Z28-Canada

Thanks for all the replies guys, all of this info helps. This q-jet is as old as the car, and has never been rebuilt. Still, it ran ok on the 305 until I was up in the 100-120 area. Now, with the 350, it's really hard to tell if it is fuel that's the problem, because I'm having other issues as well (rocker adjusment, ignition timing). I have been talking with my local hot rod shop, and I can get a new Edelbrock fuel pump, and Edelbrock 650cfm (PN 1806) for 400 bones. I'm thinking if I go that route, then at least fuel won't be an issue. Won't be throwing the q-jet in the trash though, want to rebuild it anyway. Now, to the engine forums to talk about valve adjustment

five7kid

iTrader: (14)

I missed the part where the fuel pump is known to be bad.

Brando5641

iTrader: (-1)

Go with the edelbrock.

For a daly driver IMO they are the best. I have one on a stock 350 in my 89 and it is best (reliable) carb i have ever owned. I rebuilt it and put it on and havent touched it sence. It isnt no race car but i would drive that thing anywhere.

five7kid

iTrader: (14)

You must never have had a CC carb, then.

84-Z28-Canada

Hi guys, thanks for the responses. To clear things up, mine is not a CC qjet, it's just a standard, electric choke qjet. Also, my fuel pump isn't known to be bad, but the deal at the local hot rod shop is more or less "Buy the Edelbrock 1806 Carb, get the Edelbrock Fuel pump for 75% off" or something like that, so why not? I haven't had much time to deal with the carb related issues, because the new motor is doing all kinds of weird things related to valvetrain and timing. Wants all kinds of timing to idle , and pings at pretty much any advance. Started a thread about that in general engine. My fuel pump is the original from the 350, which is a 70's block, so I figured swapping out a 30 yr old fuel pump couldn't hurt the car any. This aft is rocker arm adjustment.

Apeiron

Why not? Because it's an inferior carb to the one you already have.

cc 82Z-28

iTrader: (7)

When I had my 355 in my z, I ran a holley 670 avenger with the vacumm secondaries and electric choke. It worked great with no real adjustments other than idle screw when I put it on and I ran that combo for about 5 years before building my 406 and the motor has the holley 770 avenger on it and it too has been no problem going on 3 years now. Just make sure your fuel pressure is where holley recommends. Next for me is aftermarket EFI hopefully next year. Had the car running yesteday for the first time since late November, carb still works great.

84-Z28-Canada

hi guys thank you for all of your responses. I'm thinking that my issue right now is because I don't have the valve train set-up properly. If the intake valves are remaining open then I lose vacuum and she dies. this I understand. I have had the opportunity to pick up a holley 670 avenger as well it's nice to hear positive reviews for them. In terms of wallet power staying with the q-jet is obviously my best bet...not to mention the serious support they get on these boards. As long as I can make it run right on the motor I will use it. And I solemnly swear to do my damndest to make it work before switching to something else. In the meantime...just wish me luck on getting the thing running properly in the next month.....i'm losin my garage fellas. The wife isn't leavin but the house is sold....so I have exactly one month to have that car cruisin. Wish me luck guys

Brando5641

iTrader: (-1)

what??


Do you know how to set the lash?

84-Z28-Canada

Just indicating how fast it needs to be done. yes I do, I'm just into fine adjustment now.