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ONE LAST Q-Jet Idle question

Can Can

Can Can

Pusher Man
Joined
Feb 17, 2000
Posts
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Location
Cochrane, Alberta, Canada
After fixing a vacuum leak and having to mess around with my high idle, I have one last issue to solve on my 84.

In Park, my low idle is fine. But when I put her into D the idle drops WAY too low. I don't have a tach, but I'd be willing to guess that my idle in Park is around 700 RPM and that it drops down to about 350/400 RPM in D.

What the heck is causing this problem? Other than that the truck runs like a top. This carb has been driving me up the wall for 2 friggin weeks......
 
Honestly I can tell you to get rid of that quadra Junk and buy a edelbrock or carter carb they work much better but just my two cents....Jason
 
Maybe a timing issue?? All I can come up with, idle is controlled with idle mix, you set them for best idle mix, and thats that, unless the engine has been modified a lot, then you have problems with idle stability.
 
[ QUOTE ]
Honestly I can tell you to get rid of that quadra Junk and buy a edelbrock or carter carb they work much better but just my two cents....Jason

[/ QUOTE ]

wow, you wheel anything bumpy? hilly? a carter or edelbrock? check the castings, same thing these days /forums/images/graemlins/rolleyes.gif when's the last time you saw a carter/edelbrock (both mabe by weber) go farther up a hill than a q-jet? get your facts straight before shooting off your mouth. there's reasons why people use q-jets.

-Scott
 
That's why I'm kinda confused, Dorian. This boggy idle in D was a kind of sudden onset thing. I hadn't been messing with anything under the hood before it happened, either. Like I said, the only time I notice a problem is at idle in Drive...... /forums/images/graemlins/confused.gif
 
I had a quadra junk and I can tell you that my carter can climb hills with the best of them for you concern I have tried both and have found that the carter does run better so i have done my homework....Jason
 
Could you please refrain from hijacking my post? Starting a pissing match when I'm trying to get help is rude......And just so you know, telling someone that their gear sucks is a great way to become a member of the CK5 shitlist.

But since you can't seem to stay on topic, here's my 2 cents: A large percentage of the guys here run Q-Jets. Saying that your Carter is better makes you sound pretty uninformed.

Wanna argue with the pros? Why not tell Grim-Reaper that his Q-Jets suck. He knows more about carbs than you know about your entire truck.
 
I saw this earlier today and I didn't have anything to contribute. I'd like to think I know a lot about Quadrajets but I've got the same problem. I figured it was merely my cam.

I have my idle set to ~1000rpm in park but when I put it in gear it drops to around 550rpm. It's a kind of lopey cam that only produces around 13" of vacuum.

The only thing I can think of is to set your idle mixture screws for when it's in gear.
 
Your idle is set at 1000 in Park? Does it feel like that setting is too high? My 305 sounds like it's pretty comfy at 700 RPMs, but I might try bumping it up closer to 1000 and see if that smooths out the idle in D.

I'd still like to know why this issue seemed to appear overnight. Maybe all the fawking around I did to fix my initial problems made me oversensitive to how my truck is running...... /forums/images/graemlins/smirk.gif
 
Yeah, it does seem a little high. However, when I had my 350 in there it would barely idle at 850 and drop to 475 when I put it in drive.

I, myself, would rather have the throttle response in gear than have a nice low idle. Plus, I've learned if you have a low idle while in gear then if your back tires lock up under hard braking it'll stall.
 
free idle is usualy around 700/750, and droping to 500-550 in gear..depending on the torque converter...lock-ups have a higer stall speed, and drop less...It could be the torque converter
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if you didn't change anything, and fixed all the vacc leaks..it could be the ignition timing...DO you have a computer or ESC...??
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Non-computer carbs, run with the distributor vacc advance connect to manifold vacc, not ported..any of the little vacc ports, except the one on the lower passenger front....with the timing set with the vacc disconnected...does the ignitin advance when you hook up the vacc advance..???
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check the vacc diaphram with a vacc pump and gage..it shouldn't leak..and should advance and hold

You could have a small leak in the vacc advance, causing it to loose advance when the idle speed/vacc drops...and retarding the timeing, causing it to bootstrap slower...
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If you changed the cam causing a change in idle vacc and a big adjustment in throttle plate angel to maintain idle speed...there are two simple tricks to fix the problem..

Set the idle speed, remove the carb and turn over...look at the throttle plates where they contact the body near the idle needle jet...there is a "vertical transition slot"..it should have only about 1 ro 2 mm of slot showing..if more...i.e. the throttle is open furter..drill two .030 holes, one in each bore, about 2-2.5mm back from the front edge of the plate...install the carb, check speed, pull carb and look at slot...enlarge there holes about .010 at a time until you get the right amount of idle opening...

What happens on emission carbs, with "bigger cams", vacc drops at idle, needing more throttle opening at idle..it cause the throttle plates to run not on the ilde system but on the transition system..this makes the idle speed erratic and difficult to adjust...
/forums/images/graemlins/cool.gif /forums/images/graemlins/truck.gif
 
Sudden onset pretty much rules out a nasty cam doesn't it? /forums/images/graemlins/smile.gif

Here's an odd question. Are you sure your tach is correct? Have been talking with my dad about his truck, and he mentions how many RPM's it turns @60 or 70mph, and that maybe he should drop to a numerically lower gearset. Funny thing is, you do the math, and it *can't* be running as high as it reads, even figuring in tire height difference between advertised/actual, etc. What it looks like is that it's actually reading on a 6 cylinder scale, which on a V8 means 25% higher readings than actual...

I know I'm kinda veering off topic, but I can see that 25% difference at idle speeds causing some real problems. Strange, but the engine *sounds* like it's turning the RPM the tach says, but it's just not possible based on all the other data.
 
Yep......unless the camshaft fairy installed one in my truck while I was sleeping!!! /forums/images/graemlins/wink.gif

I don't have a tach- when I was talking about RPMs I was doing it by sound only. I'm pretty sure the problem I'm dealing with is something I personally won'y be able to fix, but lucky for me there's a great carb guy here in town.

When I get all this stuff figured out I'll post an update.
 
that is one great Q-Jet link

Please excuse the interuption as this has already been an attempted highjack already early on, but thanks for the great Qjet link Triaged. I highly recommend reading it. I don't know how good the info is yet but will find out when I try it. Thanks

Rich
Q jet Tech
 
[ QUOTE ]
buy a edelbrock

[/ QUOTE ]

lies
stay away from edlebrock...im sorry Mr Bob Edlebrock...but you make Edlejunk...go holley

yur crap has pained me long enough...im about to take a dump in my 600 and mail it to him
 
i recently picked up the Doug Roe book on quardajets. great book and more info then i'll ever use, but excellent tech on how a q- jet works.

as for your problem, i agree with the above post. sounds like vacuum and or timing problem. but it could be other things. you can get a rebuild kit for under 20 bucks and clean it up and rebuild it in an hour or two.

good luck, they are geat carbs when they work right- next best thing to fuel injection /forums/images/graemlins/thumb.gif
 
[ QUOTE ]
Non-computer carbs, run with the distributor vacc advance connect to manifold vacc, not ported..any of the little vacc ports, except the one on the lower passenger front....with the timing set with the vacc disconnected...does the ignitin advance when you hook up the vacc advance..???

[/ QUOTE ]

are you sure this is correct? i'm pretty sure i run my distrub off the ported vac and i don't have a CCC. i thought manie vac causes too much advance at idle. i could be wrong though. /forums/images/graemlins/tongue.gif
 
I'll second the book. I didn't think I could do a good rebuild on a quadrajet until I got it. Don't be so sure about not using a lot of the information. It's kind of like other things, once you learn a little about them you get hooked and start to get more interested in how they work and ways you can improve your performance.

I skimmed most of the responses, but if it happened overnight, did a v. hose come loose? Is your choke not opening completely? Might be your dist. slipped.

BTW. not trying to hijack a post, but got a quadrajet on the new 350 in my black 84 that my brother in law has now(Dam Him!!!) /forums/images/graemlins/grin.gif. I can't take credit for it since it was profesionally set up for the truck. It pulls like fuel injection until you open the secondaries. (Then it's a lot more fun) Can't beat it for off road.
 
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