Q-jet Problem @ Higher Rpm. - 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 10-20-2011, 11:44 AM
adantessr's Avatar
'23 T-Bucket Pickup
 
Last wiki edit: Troubleshooting ignition Last photo:
Join Date: Jun 2010
Location: South Charleston , WV
Age: 62
Posts: 1,549
Wiki Edits: 3

Thanks: 43
Thanked 17 Times in 15 Posts
Q-jet Problem @ Higher Rpm.

Okay the weather is bad so I'm back. I have a Q-jet carb installed on a bone stock '91 305 truck engine. I rebuilt the carb with a kit from Cliff Ruggles and made all 14 adjustments according to the literature that came with the kit. I was not able to make the PTA respond with the .073 jets so I replaced them with .069 jets. The carb has great response and idles and cruises great. The problem is that at about 4000 rpm the engine starts popping/ backfiring in the exhaust, when I have my foot on the floor. If I let up and let it upshift, it smooths out, but I would rather not have to do that. BTW this is in my 1800 lb T-bucket with a 700R4. Any ideas, guys ? P.S. This carb did the same thing on my 355 with a turbo 350. It ran fine with the edelbrock carb that I had on it previously. So I feel pretty sure that the problem is the carb. Thanks, Big Al
Attached Thumbnails
Click image for larger version

Name:	HENRY BRAKE PEDAL003.jpg
Views:	66
Size:	1,017.6 KB
ID:	59058  

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 10-20-2011, 12:15 PM
Registered User
 
Last photo:
Join Date: Oct 2011
Location: Newton county Ga
Age: 69
Posts: 143
Wiki Edits: 0

Thanks: 8
Thanked 10 Times in 8 Posts
What rods are they in the jets? Did you try it with the larger jets even tho the apt wasnt doing nothing? Cause thats a BIG jet change if using the same rods.

That light of weight the engine isnt loaded much so the vac. is prob. high more than if it was in a heavy car with high gears and such. So cause of that the power pist. spring need to be lighter than normal.
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 10-20-2011, 03:16 PM
adantessr's Avatar
'23 T-Bucket Pickup
 
Last wiki edit: Troubleshooting ignition Last photo:
Join Date: Jun 2010
Location: South Charleston , WV
Age: 62
Posts: 1,549
Wiki Edits: 3

Thanks: 43
Thanked 17 Times in 15 Posts
Quote:
Originally Posted by gonefishin'
What rods are they in the jets? Did you try it with the larger jets even tho the apt wasnt doing nothing? Cause thats a BIG jet change if using the same rods.

That light of weight the engine isnt loaded much so the vac. is prob. high more than if it was in a heavy car with high gears and such. So cause of that the power pist. spring need to be lighter than normal.
It had the same problem with the .073 jets. I installed the rods that Cliff recommended. I don't remember what they are though. I thought that with the higher vacuum I would need the stiffer spring. Cliff said to use the dark blue one, which I did. Thanks for the thoughts though. I have the spring on the secondaries adjusted for the engine that it came off off (403). It may be getting too much gas for the 305. Maybe tighten the spring another 1/4 turn, but I am fishing for other's ideas. This is the 6th car I have had a Q-jet on and this is the first time that I have had this problem. I hope that I don't have to change the spring, but if nothing else works I may try the light blue spring. I don't have any hair to pull out . LOL
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 10-20-2011, 04:40 PM
Shaker455's Avatar
Registered User
 
Join Date: Mar 2009
Location: NH
Posts: 113
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Is that a early Chevy Qjet with no main airbleeds?
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 10-20-2011, 04:48 PM
adantessr's Avatar
'23 T-Bucket Pickup
 
Last wiki edit: Troubleshooting ignition Last photo:
Join Date: Jun 2010
Location: South Charleston , WV
Age: 62
Posts: 1,549
Wiki Edits: 3

Thanks: 43
Thanked 17 Times in 15 Posts
Quote:
Originally Posted by Shaker455
Is that a early Chevy Qjet with no main airbleeds?
Carb number is 17058253 off of an Olds. Bought it on ebay and rebuilt it according to Cliff Ruggles instructions using parts recommended and supplied by Ruggles High Performance. According to a Google search it is an 800 cfm carb from a 1978 Olds, so maybe I am on the right track thinking that I am overfueling and need to tighten the secondary damper spring. Suggestions ?

Last edited by adantessr; 10-20-2011 at 05:01 PM.
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 10-20-2011, 08:05 PM
Registered User
 
Last photo:
Join Date: Mar 2011
Posts: 131
Wiki Edits: 0

Thanks: 11
Thanked 7 Times in 7 Posts
To slow the secondary air flap on a Quadrajet you need to restrict the vacuum flow. You want the spring to close the flap, that's it.. It is not designed to be an adjustment.. If you look closely at the vacuum port for the pull off, you will see the end peened over. Thats how they regulate the opening of the secondary flap... It's in Cliffs book..

By the way, your in good hands with Cliff...
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 10-20-2011, 09:54 PM
Registered User
 
Last photo:
Join Date: Oct 2011
Location: Newton county Ga
Age: 69
Posts: 143
Wiki Edits: 0

Thanks: 8
Thanked 10 Times in 8 Posts
Quote:
Originally Posted by adantessr
It had the same problem with the .073 jets. I installed the rods that Cliff recommended. I don't remember what they are though. I thought that with the higher vacuum I would need the stiffer spring.
It should be stiffer, not lighter. I have a prob. gettitng my head around that some times. At least you knew I was wrong and thats good.

On the air valve the choke pull off also acts as a damper for the av and stock it will delay the opening more than if you open the hole up that is inside the nipple on most of them.
Reply With Quote Quick reply to this message
  #8 (permalink)  
Old 10-21-2011, 11:46 AM
adantessr's Avatar
'23 T-Bucket Pickup
 
Last wiki edit: Troubleshooting ignition Last photo:
Join Date: Jun 2010
Location: South Charleston , WV
Age: 62
Posts: 1,549
Wiki Edits: 3

Thanks: 43
Thanked 17 Times in 15 Posts
Thanks for the replies. It is supposed to be in the low 70's here Mon & Tues, so I may play with it a little to see what I can make happen. I am open to consider any suggestions. It is a little embarassing when somone pulls up alongside and yells "Kick it down" and it starts backfiring @ 4000 in second, about 50 mph.
Reply With Quote Quick reply to this message
  #9 (permalink)  
Old 10-21-2011, 11:55 AM
Registered User
 
Last photo:
Join Date: Oct 2011
Location: Newton county Ga
Age: 69
Posts: 143
Wiki Edits: 0

Thanks: 8
Thanked 10 Times in 8 Posts
Big Al thats right in the meat of where the sec. should be opening. I can think of a couple things you can try. 1 is to prevent the sec. from opening so it runs on just the pri. to see that it's the sec. causing the prob. And the other is to use a leaner rod in the sec. by that I mean a bigger dia. rod.

Another thing that will cause it to back fire thru the carb not the muffs is if the cam is broke or missing that lifts the sec. rod hangar. It will sound just like a burnt valve but this is not likely your prob. cause its back firing thru the pipes and not the carb but dont hurt to look. May come in handy some day tho.
Reply With Quote Quick reply to this message
  #10 (permalink)  
Old 10-21-2011, 12:16 PM
adantessr's Avatar
'23 T-Bucket Pickup
 
Last wiki edit: Troubleshooting ignition Last photo:
Join Date: Jun 2010
Location: South Charleston , WV
Age: 62
Posts: 1,549
Wiki Edits: 3

Thanks: 43
Thanked 17 Times in 15 Posts
Quote:
Originally Posted by gonefishin'
Big Al thats right in the meat of where the sec. should be opening. I can think of a couple things you can try. 1 is to prevent the sec. from opening so it runs on just the pri. to see that it's the sec. causing the prob. And the other is to use a leaner rod in the sec. by that I mean a bigger dia. rod.

Another thing that will cause it to back fire thru the carb not the muffs is if the cam is broke or missing that lifts the sec. rod hangar. It will sound just like a burnt valve but this is not likely your prob. cause its back firing thru the pipes and not the carb but dont hurt to look. May come in handy some day tho.
Thanks gonefishin'.. I rebuilt the carb and it has a new lifter cam. When I first installed the carb and took it for a ride with the air cleaner off, I could see gas coming out the top of the secondary bores and spraying on the windshield at the same time the backfiring in the exhaust occurs. Thought maybe it was because I didn't have the air cleaner on. ( I just remembered this, been over a year ago. ) More food for thought.
Reply With Quote Quick reply to this message
  #11 (permalink)  
Old 10-21-2011, 12:32 PM
cobalt327's Avatar
WFO
 
Last wiki edit: Intake manifold
Last journal entry: 1980 Malibu Wagon
Last photo:
Join Date: Mar 2009
Location: Atlanta
Age: 59
Posts: 5,037
Wiki Edits: 1616

Thanks: 128
Thanked 597 Times in 546 Posts
When you had this carb apart, were the secondary tubes tightly in place? They have been known to fall completely out and will be found laying in the bottom. There should have been at least four, and some carbs had six.

There are secondary enrichment holes in the secondary bores of the air horn. Most are above the air valve, located on the wall closest to the inside of the carb. Some were below the air valve and few have a slot cut out of the air valve flaps where they are located. Be sure the holes are open to the tubes. The tubes can be driven in TOO far, this will keep the secondaries from getting extra fuel just as the air valve begins to open. This acts like an accelerator pump except w/o a pump- a pressure drop past the edge of the air valve pulls fuel into the airstream.

The tubes that are connected to the enrichment holes are fed by a well that is filled by tiny (about 0.028") holes in the float bowl. If these small passages are not allowing the wells to fill, the secondary enrichment circuit will not work and you will get a lean condition.

Also be sure the secondary discharge tubes' air bleeds are open as they should be, if they're not it'll be too rich. And by the sounds of it, it may be too rich. Swapping to a leaner secondary rod isn't a bad idea if you want to try something easy that will tell you if it's too rich. Worth a try. If you block the secondaries from opening be sure it doesn't in any way cause the throttle to stick.

Last think I can think of is to be sure the choke is not able to close under hard acceleration.
Reply With Quote Quick reply to this message
  #12 (permalink)  
Old 10-21-2011, 12:44 PM
adantessr's Avatar
'23 T-Bucket Pickup
 
Last wiki edit: Troubleshooting ignition Last photo:
Join Date: Jun 2010
Location: South Charleston , WV
Age: 62
Posts: 1,549
Wiki Edits: 3

Thanks: 43
Thanked 17 Times in 15 Posts
Quote:
Originally Posted by cobalt327
When you had this carb apart, were the secondary tubes tightly in place? They have been known to fall completely out and will be found laying in the bottom. There should have been at least four, and some carbs had six.

There are secondary enrichment holes in the secondary bores of the air horn. Most are above the air valve, located on the wall closest to the inside of the carb. Some were below the air valve and few have a slot cut out of the air valve flaps where they are located. Be sure the holes are open to the tubes. The tubes can be driven in TOO far, this will keep the secondaries from getting extra fuel just as the air valve begins to open. This acts like an accelerator pump except w/o a pump- a pressure drop past the edge of the air valve pulls fuel into the airstream.

The tubes that are connected to the enrichment holes are fed by a well that is filled by tiny (about 0.028") holes in the float bowl. If these small passages are not allowing the wells to fill, the secondary enrichment circuit will not work and you will get a lean condition.

Also be sure the secondary discharge tubes' air bleeds are open as they should be, if they're not it'll be too rich. And by the sounds of it, it may be too rich. Swapping to a leaner secondary rod isn't a bad idea if you want to try something easy that will tell you if it's too rich. Worth a try. If you block the secondaries from opening be sure it doesn't in any way cause the throttle to stick.

Last think I can think of is to be sure the choke is not able to close under hard acceleration.
Thanks for the thoughts Mark. I really took my time when I rebuilt this carb and soaked it in laquer thinner and made sure to blow out all passages while the carb was still wet. I also made sure that everything was tight. I am getting ready to go out to the garage to take another look at everything. Thinking of bending the rod hangers a little to see if that helps. BTW I did make all 14 adjustments and the choke is held wide open by the linkage under full throttle. Never had a carb do this, so it is a bit frustrating. 800 cfm is definitely too much for a 305 so it seems to have to be an overfueling problemm that needs to be adjusted out of it somehow. Thanks again. Big Al
Reply With Quote Quick reply to this message
  #13 (permalink)  
Old 10-21-2011, 06:26 PM
cobalt327's Avatar
WFO
 
Last wiki edit: Intake manifold
Last journal entry: 1980 Malibu Wagon
Last photo:
Join Date: Mar 2009
Location: Atlanta
Age: 59
Posts: 5,037
Wiki Edits: 1616

Thanks: 128
Thanked 597 Times in 546 Posts
I missed your reply to gonefishin as I was typing while it was being posted. The fuel coming from the secondaries- I'm guessing the air valve was tipped open? If so, there could be two things going on:

First is the secondary rods being way too rich combined with the air valve adjustment being too light.

Second, if the air valve wasn't opening as it should (either because the pull off wasn't releasing under low vacuum conditions, or the air valve was adjusted too tight or if it were binding because the two rear screws were over tightened), the secondary throttle valve (not air valve) will still open fully at WOT and if the vacuum builds enough (like at 4000 RPM) it will pull fuel from the secondary discharge ports (the large tubes that angle into the secondary side of the carb). This will cause a way over-rich condition and I'd also expect fuel to be coming from around the air valve- even w/it being closed.

If someone were to follow you to watch the exhaust when this was happening, they should see black from the exhaust if it's over rich.
Reply With Quote Quick reply to this message
  #14 (permalink)  
Old 10-21-2011, 06:41 PM
adantessr's Avatar
'23 T-Bucket Pickup
 
Last wiki edit: Troubleshooting ignition Last photo:
Join Date: Jun 2010
Location: South Charleston , WV
Age: 62
Posts: 1,549
Wiki Edits: 3

Thanks: 43
Thanked 17 Times in 15 Posts
Quote:
Originally Posted by cobalt327
I missed your reply to gonefishin as I was typing while it was being posted. The fuel coming from the secondaries- I'm guessing the air valve was tipped open? If so, there could be two things going on:

First is the secondary rods being way too rich combined with the air valve adjustment being too light.

Second, if the air valve wasn't opening as it should (either because the pull off wasn't releasing under low vacuum conditions, or the air valve was adjusted too tight or if it were binding because the two rear screws were over tightened), the secondary throttle valve (not air valve) will still open fully at WOT and if the vacuum builds enough (like at 4000 RPM) it will pull fuel from the secondary discharge ports (the large tubes that angle into the secondary side of the carb). This will cause a way over-rich condition and I'd also expect fuel to be coming from around the air valve- even w/it being closed.

If someone were to follow you to watch the exhaust when this was happening, they should see black from the exhaust if it's over rich.
First gotta find somebody who can keep up with me when this is happening. Just kidding. I can see the carb pretty well from the driver's seat so I am going to take it for a drive with the air cleaner off again so I can get a better idea of what is going on. Then to watch for 'smokey' to not be around while I am testing. May be can get the wifey to follow me in her 'Vibe' For what it's worth I have tried it with the linkage taken off the pulloff and also with the spring loosened up to 1/2 turn. The air valve plates do move freely. Thanks Mark for more things to look at. Supposed to be high 50's tomorrow so I may tinker. I'll let you know how it works out. I am tired of being in the house since Tuesday. Rainy arthritis pain....Big Al
Reply With Quote Quick reply to this message
  #15 (permalink)  
Old 10-21-2011, 06:55 PM
cobalt327's Avatar
WFO
 
Last wiki edit: Intake manifold
Last journal entry: 1980 Malibu Wagon
Last photo:
Join Date: Mar 2009
Location: Atlanta
Age: 59
Posts: 5,037
Wiki Edits: 1616

Thanks: 128
Thanked 597 Times in 546 Posts
I saw your thumbnail on the "Where's Randy" thread... Dude! That's WAY to much fun!!!

I'm avoiding that thread, pretty much a no-win situation for someone who finds themselves on the wrong end of:
Quote:
We have a list of repeat offenders in a special thread in the moderating forum of those that may require special treatment because of their behavior.
Kind of like having two strikes called on you while you were still suiting up, IMO. The rules are what they are- just seems like they aren't equally applied, at least not in a case where some are already one step away from a ban while others- in a position where they are supposed to be an example to be followed- can rant and rave and call folks names, etc. w/o any public "consequences". At least the posts went to the dump - an apt place for them, BTW- where they will fester for a while longer before being well and truly dumped for good.

But I digress. As long as you keep hunting for the problem w/your Q-jet, the least I can do is offer suggestions to keep you busy and out of the pool hall!
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


Similar Threads
Thread Thread Starter Forum Replies Last Post
higher reving v8 nate4567 Engine 55 04-01-2009 09:21 PM
higher rpm shifts novapower Transmission - Rearend 1 10-22-2008 10:55 PM
How do I get my SBC to rev higher? HammerGVette Engine 15 12-06-2007 08:36 PM
higher-octane? Pontiacman Introduce Yourself 3 01-07-2006 06:48 PM
How have the higher gas prices..... Malibucdl Hotrodders' Lounge 11 05-14-2005 12:47 PM


All times are GMT -6. The time now is 09:38 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.