Need Help from experienced QJet guy - Hot Rod Forum : Hotrodders Bulletin Board
Hotrodders.com -- Hot Rod Forum



Register FAQ Search Today's Posts Unanswered Posts Auto Escrow Insurance Auto Loans
Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Engine
User Name
Password
lost password?   |   register now

Reply
 
LinkBack Thread Tools
  #1 (permalink)  
Old 09-04-2002, 07:02 PM
Registered User
 
Join Date: Sep 2002
Location: SE Penn.
Posts: 5
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Post Need Help from experienced QJet guy

I'll apologize for the length of this up front, but want to include everything so the whole picture is there for
diagnosis.

Bottom line with my problem is that my 455 is down on power, and I am convinced it's all related to the QJet. This
455 is in a 67 Jeep Gladiator Full Size pickup weighing around 4800 lbs empty. It is 4wd running a very heavy duty
T18 4 speed into a Dana 20 (all gear, part time transfer case-meaning the front axle is not driven unless it's
"in"4wd)

Net effect: lots of wide, coarsely geared cogs spinning in lots of 90W oil. Every component in drivetrain has been
completely rebuilt with new everything, and works as new.

Motor:

74 455 (462) Buick with all the usual oiling mods,
cut to "0" deck with stock dished 8.5:1 pistons
68 heads with three angle, backcut, gasket matched, and light porting/clean up intake side cut for cut block
stage1 springs, stock steel rockers, not sure how many times head was cut prior, but again surfaced
Brute timing set with 9 keyway gear
Oil pump plate and adj regulator, mellings otherwise
Fel pro blue head gasket
Edelbrock performer
Modded Qjet
Hei total rebuild mech only curved from 850-2600 all in
Timed to 10 before initial, about 30 total when all in
Jim Burek's 224/236 cam (~ 500 lift)
Headers
3" exhaust, but short-about 1 ft of pipe from collector to muffler which
is a 30" 19 dollar pep boys 3" turbo muffler then another foot of pipe and 3" turnouts

TRANNY
Manual
1st 6.32
2nd 3.09
3rd 1.69
4th 1.00
REV 7.44

Rear(s)
3.73:1
Tire Size
33" diameter

Cam was dialed in with wheel to 112 deg.
Made 30 deg mark on balancer, and advance is correct.

Now to the problem(s)

I am running a dual pattern new Edelbrock and a 71
455 Qjet which has been cooked, rebushed and dyed.
various mods to Qjet in keeping with the the gospel according to Roe (drilled pickup tubes, 90 deg
secondaryopening, etc. still has stock power piston spring) Drawing about 14-15 in of vac

Idle:
Idles fine, but could be better, based on the fact that on all of my other QJets, I could get the idle screws to one
setting where it was obviously correct. Moving the setting even 1/4 turn from the correct setting would show a
negative idle change. On THIS motor, I can move both idle screws 2 whole turns before there is a change in
idle,anywhere in this 2 turn range there is no change.

I tried inserting a thin screwdriver in the vent tube to see if the power piston was seated at idle, and it does seem
to be seated. When the motor is off, I can feel the power piston going up and down using this method. Also, there
is no change in idle when I do this, so I *think* the piston spring is OK for my app, but comments welcome on this
point.

Base gasket.
I understand there are two base gaskets (at least)for QJets, one that shrouds vac ports that affect idle in the
front, one that does not. Which one do I need for a 71 Qjet on the new dual patt. Edlebrock manifold? When I was
GSing or Skylarking in the 80s, I would use these very nice thick gaskets with the nylon inserts on iron manifolds.
Can't seem to find them now.
Comments?

Secondaries:
I am aware of the "drill the seconday pull off" procedure to get the pull off to be more aggressive. The problem is
that my secondaries are not opening, or barely opening with a new undrilled pull off with a tiny port! To diagnose
this, I unhooked the hose from the pull off, and plugged it with a screw. VIOLA! Secondaries! Of course they just
flop open with a small lag without the pull off, but they open. Still, something seems wrong with that-there isn't
the dramatic du-WAH I've always had. It climbs lazily. 4th gear is pathetic in this regard.
3rd is the monster gear in this vehicle, if you look at the chart above on the tranny, 1st is a granny creeper, I
usually pull out in 2nd, and even that is a very short gear. No power problems in 2nd, but then again the gear is so
aggessive that even on two barrels, I probably wouldn't
notice any performance issues. (can spin 33" tall
12.5" wide tires at one RPM all day long)

Oh yeah, secondary air door adjusted at 1/8 turn past "no tension" on spring. Can't understand why pull off seems
to be fighting secondaries opening.

I need to get these issues fixed before I can even dream about trying different rods/jets.
It's been awhile and many details since I built the QJet, but I think I went with the conventional 2 sizes over stock
to start with on the jets, and adjusted the rod size accordingly, but will most likely be looking at that based on
what you guys might have to say.

One last thing- choke.
Why Edelbrock chose not to cast a choke spring well in the intake is beyond me. I ended up looking through a Borg
Warner catalog and picking
a choke spring that worked with a rod I bent up, and I do have nice fast idle, and the idle cam drop down as you
would expect, but what do most folks do for a choke on a "spring-and-rod" style
QJet with a new Edlebrock manifold? (which I think is most Buick QJets of our era)

What do I think? I think I might have the wrong
base gasket, or the gasket isn't cut right, but I can't just go and buy every gasket I can find and try them all, I'd
like some input from someone who has been here.

Thanks for sticking with this long post, I am out of answers, and frustrated at the money and time spent thus far
without the performance I know this thing could have!

Brad

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 09-04-2002, 07:55 PM
4 Jaw Chuck's Avatar
Hotrodders.com Moderator
 
Last photo:
Join Date: Mar 2002
Location: Manitoba, Canada
Age: 46
Posts: 4,953
Wiki Edits: 0

Thanks: 2
Thanked 88 Times in 71 Posts
Post

You could spend a small fortune trying to get that Quad working with that motor and you might one day get a setup that works...sometimes. You obviously know your stuff so I will be blunt, toss the Quad and get a double pumper Holley...850 if I were you. The problem lies in the fact that you are reaching the limits of what a Quadrajet can do, even Chevy put Holleys on their High perf wild cam engines. The knowledge that is out there for tuning a Quad was gained from racing them in restricted classes where you had no choice, in almost every instance a Holley carb change would improve power for these guys but they are stuck with the Quad. Your not.

I could go on and on describing why a Quad is not a capable high performance carb and probably piss a lot of people off. There is nothing wrong with them but they were never built to accomodate what you are attempting. You don't need to become a carb redesigner when you have other options. I prefer not to hit my head against a wall when I can just walk around it, if you walk this way it won't hurt anymore...I promise. The Holley knockoffs are good too like the Demons etc. I only wish they still made Predator carbs, now that was a mixer!
__________________
Outlawed tunes from outlawed pipes
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 09-04-2002, 08:56 PM
Registered User
 
Join Date: Sep 2002
Location: SE Penn.
Posts: 5
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Post

Well, I have considered that, also considered Mr. Hammer meeting Mr. QJet! The thing is I know of too many guys running real quick (like 12s) with Qjets on nore aggressive motors than I have in all flavors of GM musclecars and even boats like Catalinas, Wildcats, Vista Cruisers, etc.

I hate to give up on the QJet if there is a simple solution to this problem. I've always had great running Qjets, and thought I was pretty good with them until this motor!

Maybe I eventually will get sick of this and go Holley, but in the past I have had Holleys perform just as well in timed runs as a QJet, but the MPG is always worse, and supposedly a QJet is a better off road carb.

This truck is intended to be a beefy work horse (which it is), somewhat trail worthy (it's that as well), and a serious threat to Ford Lightning pickups. The last thing it aint, but it could be, if it were running to it;s potential-which it aint.

After asking on other groups what do ya think, I get a lot of out there guesses, but no actual help like "Oh-I had that and here is what I did"

Time and theory, and lotsa QJets i got, money I aint got. Hoping someone chimes in with some QJet tech that I am overlooking.

Brad
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 09-04-2002, 10:45 PM
4 Jaw Chuck's Avatar
Hotrodders.com Moderator
 
Last photo:
Join Date: Mar 2002
Location: Manitoba, Canada
Age: 46
Posts: 4,953
Wiki Edits: 0

Thanks: 2
Thanked 88 Times in 71 Posts
Post

Have you tried an unmodified Q-jet? Perhaps there is something wrong with that one, more than once I have seen bent secondary needles that prevent the secondaries from closing or even opening at all. It doesn't take much of a bend to screw them up, a good straightedge and comparing them to each other is a good method. It kinda sounds like a binding condition is preventng your secondary actuation.
__________________
Outlawed tunes from outlawed pipes
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 09-05-2002, 05:17 AM
WoodsEdge's Avatar
Member
 
Join Date: Apr 2002
Location: Hoot Owl Ridge in S. Mtns. N.C.
Posts: 406
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Post

I agree with 4-Jaw, start with a stock 750cfm
Q-jet, They range from 600-750, that will give you a base. Then start modifying 1 step at a time. Good all around carb, but can be touchy.
Jack
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 09-05-2002, 02:06 PM
Registered User
 
Join Date: Sep 2002
Location: SE Penn.
Posts: 5
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Post

I started with brand new rods and jets from edelbrock, which in itself doesn't mean they weren't bent, but I did check that. I don't want to come off like "everything you guys say is wrong" because sooner or later someone may come up with something that I never ran into or never thought of. I appreciate the input!

This I can tell you:
I am using the bigger 800 cfm Qjet which
is accepted by the Buick 455 guys as the carb to use in my and all 455 apps.

the mods that I did were light, such as:
drilled the pick up tubes (as in the A/C Cobra QJet)
ground the limiting casting on the body so the secondaries can open 90 deg
used the "big" needle and seat
ground and JB welded the fuel well plugs

This is all pretty standard stuff.

I checked the air horn for warp.

The idle screw unresponsiveness is usually indicative of a QJet which has had the idle circuit modified by drilling the passages larger-
this I did not do because you don't really know what you are going to have until you run the motor.

I can say that it is also a symptom of having the primary butterflies open too far into the transitional circuit where it is pulling gas through the transitional slots- this is also not the case.

I *did* manage to find out the following info which may be on the right track for the idle screw problem:

The idle circuit draws it's vac from the base. Some QJets do not have a slot cut into the base plate which force you to use the QJet base gasket which is OPEN in the front-some QJets which have the slot can use the "closed in the front" type of base gasket because the slot extends past the closed portion of the gasket allowing the idle circuit to draw vac. At this point I am unsure (many many details ago) which gasket and slot type I am running. Add to that issue the following:

I am running a dual pattern (not to be confused with dual PLANE) Edlebrock Performer intake. Meaning that it can bolt a Holley or QJet. I have read that with the crappy knock off gaskets that are available these days that they do not seal right on dual pattern intakes, giving a vac leak that affects the idle circuit, AND is almost undectable. The cure it seems is oddly enough to run one of those adapter spacer plates under the QJet, which with the gaskets available will allow
the spacer to seal to the intake nicely and the QJet to seal to the spacer nicely, AND has the added advantage of offering better off idle reponse, and curing the exact problem I am having with the idle adjustment. This I learned on a Corvette web site from a guy who claims he has done this 6 different times. He claims same symptom, same cure in each case.

Since I have some of those spacers lying around from previous projects, it can't hurt to try it.
I will post my findings when I try it for others who are banging thier heads.

BTW, the gasket which is supposed to worm in all cases the the 1/4 " thick with nylon spacer gasket
which is also open in the middle, and open up front on the idle circuit Borg Warner part number
14297.

Secondaries:
After talking to a local business that does nothing but carb and ignition for drag/cirle track
racing, I told them that I did the "1/8 turn past no tension" adjustment on my secondary air door.
They said that what may be happening is that I think my secondaries are never opening because the air door is always open, and that they found they usually it takes more than the 1/8 turn as recommended by the Doug Roe book on QJets to get them to run right.

Again, I will post the results when I try this.

Brad
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 09-06-2002, 02:28 AM
roys63's Avatar
Member
 
Last photo:
Join Date: Dec 2001
Location: Nc
Age: 63
Posts: 907
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Wink

How about your cam timing 112 thats all top end power-torque, sounds like you want more bottom end power? try advancing you cam timing to 108 or so.now you have more fine tuning to play with.Just a thought to ponder.
Reply With Quote Quick reply to this message
  #8 (permalink)  
Old 09-06-2002, 02:31 AM
roys63's Avatar
Member
 
Last photo:
Join Date: Dec 2001
Location: Nc
Age: 63
Posts: 907
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Post

And you need a gear change with the 33s
Reply With Quote Quick reply to this message
  #9 (permalink)  
Old 09-06-2002, 06:51 AM
4 Jaw Chuck's Avatar
Hotrodders.com Moderator
 
Last photo:
Join Date: Mar 2002
Location: Manitoba, Canada
Age: 46
Posts: 4,953
Wiki Edits: 0

Thanks: 2
Thanked 88 Times in 71 Posts
Post

I would get another complete carb and try it, then mix components from the two until you isolate the problem with yours. I still think another carb is a lot easier to do and a Holley or Edelbrock carb is a hell of a lot more tunable than a Quad. Sometimes you need to step back and look at what your doing and divorce yourself from the aggravation. Your idle mixture insensitivity is normal for a factory style carb facing mixing fuel for a radical cammed engine, another good reason to improve your carburation. Quads are great carbs but they have serious limitations much like Autolites do. I have spent a lot of time working on Q-jets and althought they are good carbs for the street as soon as you try to make them run with radical cammed engines they are just not capable of coping with the irregular vacuum fluctuations and especially with long overlaps they perform unpredictably. Holleys are much more unsophisticated and your carb needs to be with a big cam, sensitive carbs are great for mileage but don't work on sledgehammer equipped vehicles. The passages are simply just not big enough and are in the wrong location for long overlap cams, you can spend your time reinventing the wheel or buy a perfected one off the shelf...it's up to you.

Good luck.
__________________
Outlawed tunes from outlawed pipes
Reply With Quote Quick reply to this message
  #10 (permalink)  
Old 09-06-2002, 07:10 AM
4 Jaw Chuck's Avatar
Hotrodders.com Moderator
 
Last photo:
Join Date: Mar 2002
Location: Manitoba, Canada
Age: 46
Posts: 4,953
Wiki Edits: 0

Thanks: 2
Thanked 88 Times in 71 Posts
Post

BTW a Holley carb can be modifed to work just as well offroad as any Q-jet, the mods needed are well known and easy to perform, don't believe all the hype.
__________________
Outlawed tunes from outlawed pipes
Reply With Quote Quick reply to this message
  #11 (permalink)  
Old 09-06-2002, 08:25 AM
New Member
 
Join Date: Sep 2002
Posts: 16
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Post

oh no... dont put no holly on it. thats where you could go wrong. i dont care for qjets nether but, it being that heavy(the truck) i dont think you need all that, maybe a 500 cfm 2barrel? they use just as much gas as a four barrel... but im sure you probably dont do alot of "hauling *** " in that ol jeep
Reply With Quote Quick reply to this message
  #12 (permalink)  
Old 09-06-2002, 10:27 AM
Registered User
 
Join Date: Sep 2002
Location: SE Penn.
Posts: 5
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Post

I agree with the "step away from the aggravation" comment. I hate to just blindly run away from a problem, I'd like to understand what the hell is going on. In the end 4Jaw, you may end up being exactly right- the QJet isn't up to my task.

There are a couple things I can try yet nearly for free, and I will before I bail on the QJet on this motor. I have run QJets, and got them tuned so finely on stock motors with HEI and headers that you could drop the hammer from any RPM and they performed flawlessly. I thought I was pretty good with them until this episode.

I didn't think my motor was that "radical"...
it's around 10:1 (8.5 pistons, but block cut and head math puts it around 10:1), cam is 112 centerline 224/236 dur with about 500 lift on each side. It draws about 14 in of vac, is kinda lumptiy, but not such that you can almost "count" the pulses at idle (you know what I mean). Not to mention the Rhodes lifters which smooth the low RPM. Not saying anyone is wrong, I'm just surprised at all this with the QJet on this combo.

Cam timing:
I did make one huge mistake initially, I tried actually retarding the cam thinking that I had low end to spare, so I wanted to see what I could do to get more top end out of the cam. DO NOT DO THIS! What I got was crappy running all over the entire RPM range! I had to try it to see, and now I know. I went back and dialed in the cam with a wheel and it's around 111 deg. What a HUGE positive difference that made!!

Second mistake was that because I cut the blcok so radically, I also had the heads cut on the inner manifold surface to make the intake mate right. That was OK, but what wasn't OK, was that I also tried to use the stock neoprene end seals which ended up holding the intake up away from the sides
and I got a HUGE vac leak. Took it apart, and RTV'd the end seals, VOILA! Intake dropped down onto heads, no more leak.

I expected the QJet to start behaving then, and this is when I got onto this whole quest with the carb. There are a whole lotta things I could take for granted with my old stock musclecars, but this is a new ballgame for me, the first time I built a heavily modified motor, and am learning by painful experience. <img src="graemlins/spank.gif" border="0" alt="[spank]" />

That's why we're all here right?

Even with the problems I am having, the motor starts and idles fine, and most guys would probably just figure "whatever" and leave the idle screw situation alone. Just bigs the hell out of me knowing that it's not the way it should be.

I think alot of guys bail on the QJet because they ARE complicated, and there is more Holley info out there than QJet, so they give up when if they understood, they could have fixed the problem. I don't want to be that guy. I DO know when to cut my losses however, and if after one or two more things tried I can't get around this BS, I'll have to go bigger Holley for the first time ever.

I really haven't actually tried anything yet, just trying to hash out what it could be instead of blindly doing whatever. Well, enough theory and typing- more wrenching! If anyone is interested, I'll post back what I find good, bad, or indifferent.

Brad
Reply With Quote Quick reply to this message
  #13 (permalink)  
Old 11-20-2002, 03:37 PM
jobu's Avatar
New Member
 
Join Date: Nov 2002
Location: San Diego
Posts: 18
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Post

455Jeep - How did your qjet tune up work out. I just bought a 67 Firebird 400 with an 800 cfm qjet and it was really out of whack. I started by opening up the idle mixture jets from 2 1/2 turns to 4 turns according to suggestions by Mertz et al, that immediately made a huge difference in the way it idled and ran under low load conditions. When I try to jump on it it still bogs down and hesitates and has a fraction of the acceleration I would expect from a newly rebuilt 400 (0.030 bore, crank turned, roller rockers, factory long-branch exhaust manifolds). I'm also considering dumping the qjet for a new holly 750 dp. What do you recommend?
Reply With Quote Quick reply to this message
  #14 (permalink)  
Old 11-20-2002, 04:30 PM
1BAD80's Avatar
The Smell of Nitro in the morn
 
Last wiki edit: How to adjust valves Last photo:
Join Date: Jun 2001
Location: Mich
Posts: 2,423
Wiki Edits: 2

Thanks: 0
Thanked 3 Times in 2 Posts
Post

I agree with 4 Jaw Chuck, he does really know what he is talking about. I would also recommend
A Holly carb, its all in the tuning.
__________________
Luv the smell of NITRO in the morning.
Reply With Quote Quick reply to this message
  #15 (permalink)  
Old 11-20-2002, 05:00 PM
Member
 
Join Date: Nov 2002
Location: Missouri
Posts: 104
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Post

I see idle problems on Q-Jet carbs with bigger than stock cams every now and then. What I find most of the time is the guy just turned up the idle screw to get the thing to idle that the transfer ports for the idle transfer slot is mostly uncovered. I drill a small hole in the primary throttle blades so I can take the idle screw back out. I then have a better signal in the idle circuit. I start with an 1/8 and that is a big improvement in most cases. If you would like to try this e-mail me and I will talk about some other things first. Ryan
Reply With Quote Quick reply to this message

Recent Engine posts with photos

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Hot Rod Forum : Hotrodders Bulletin Board forums, you must first register.
Please enter your desired user name (usually not your first and last name), your email address and other required details in the form below.
User Name:
If you do not want to register, fill this field only and the name will be used as user name for your post.
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On



All times are GMT -6. The time now is 04:00 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.