The 1947 - Present Chevrolet & GMC Truck Message Board Network







Register or Log In To remove these advertisements.

Go Back   The 1947 - Present Chevrolet & GMC Truck Message Board Network > General Truck Forums > Engine & Drivetrain

Web 67-72chevytrucks.com


Reply
 
Thread Tools Display Modes
Old 02-05-2017, 11:32 AM   #1
Whitelm
Registered User
 
Join Date: Apr 2014
Location: Idaho Falls, Idaho
Posts: 11
Q-jet Problems

Okay, I have waded through alot of questions and answers but I can't find anything that comes close so here goes. I ordered an new (completely re-built) Q-jet carb for my 71 k-10. I installed it and set the timing. It purrs like a kitten when idling and revs up great in park or neutral, but when I stick the truck in gear it loses power and eventually stalls when I push on the gas. I have installed a new distributor kit and fuel pump. Fuel tank sending unit is also new. The truck was running fine when I pulled the original carb.
Any ideas??
Whitelm is offline   Reply With Quote
Old 02-05-2017, 11:35 AM   #2
geezer#99
Registered User
 
geezer#99's Avatar
 
Join Date: Aug 2009
Location: Bowser
Posts: 8,888
Re: Q-jet Problems

What's your timing curve like?
What's initial timing?
geezer#99 is offline   Reply With Quote
Old 02-05-2017, 03:41 PM   #3
nonstop
Registered User
 
Join Date: Dec 2014
Location: Northern California
Posts: 337
Re: Q-jet Problems

What is the idle at? How is the mixture? Is the choke opening?

If it's just from the rebuilder, might be worth giving them a call, not that we don't want to help, just that you paid them for a service, and if it's something beyond tuning, they should make it right!
nonstop is offline   Reply With Quote
Old 02-05-2017, 05:21 PM   #4
Whitelm
Registered User
 
Join Date: Apr 2014
Location: Idaho Falls, Idaho
Posts: 11
Re: Q-jet Problems

Timing was set at 8 degrees btdc with vacuum plugged at ~750 rpm. Revving the engine to about 2500 rpm with the vacuum attached I get approximately 16 to 18 degrees past tdc. Choke is Manual so that should not be an issue. I took the truck to what I thought was a reputable mechanic to see if he had any ideas. When I got the truck back, after $100 for nothing, they had pulled the carb down and broken the Secondary Float Bowl insert. (an issue that they deny doing). I replaced the insert and put the carb back together. Because the carb was broken into National Carburetor refuses to warrantee it, so I am now stuck with what I have. I am at a loss. I have never had any of my trucks act like this. I have owned two 71's and a 70. and never seen this issue before.
Whitelm is offline   Reply With Quote
Old 02-05-2017, 05:29 PM   #5
geezer#99
Registered User
 
geezer#99's Avatar
 
Join Date: Aug 2009
Location: Bowser
Posts: 8,888
Re: Q-jet Problems

A couple thoughts!
Manual choke and your secondary insert.
You got pics so we can see what you're talking about.

And your initial timing is way low considering the elevation where you live.
geezer#99 is offline   Reply With Quote
Old 02-05-2017, 09:09 PM   #6
Dead Parrot
Registered User
 
Join Date: Aug 2012
Location: Oklahoma City, OK
Posts: 761
Re: Q-jet Problems

Pics will help. If the timing is only 16-18 advanced at 2500rpm unloaded, something isn't working correctly. Either the vacuum pot is broken/connected wrong or the mechanical advance is locked up.

Double check for a vacuum leak.
Dead Parrot is offline   Reply With Quote
Old 02-08-2017, 01:08 AM   #7
Whitelm
Registered User
 
Join Date: Apr 2014
Location: Idaho Falls, Idaho
Posts: 11
Re: Q-jet Problems

Vacuum lines are all new. No leaks are evident. Vacuum advance is new (came with the new Distributor). I rechecked the Timing curve and it registers ~28 - 30 ATDC. When I initially set the timing I went with what my Shop Manual indicated it should be set at. I am attaching some photos of the carb as it is installed. Hope they help
Attached Images
    
Whitelm is offline   Reply With Quote
Old 02-08-2017, 01:54 AM   #8
Getter-Done
Registered User
 
Getter-Done's Avatar
 
Join Date: Dec 2009
Location: TN.
Posts: 70
Re: Q-jet Problems

Does the New Gasket match the Carb and Intake manifold?
You may have a small Vac. leak because of the new gasket is not full coverage for both.
Getter-Done is offline   Reply With Quote
Old 02-08-2017, 10:38 AM   #9
geezer#99
Registered User
 
geezer#99's Avatar
 
Join Date: Aug 2009
Location: Bowser
Posts: 8,888
Re: Q-jet Problems

Bump up your initial to 14.

What's this secondary float bowl insert thing you're talking about?
geezer#99 is offline   Reply With Quote
Old 02-08-2017, 11:38 PM   #10
Getter-Done
Registered User
 
Getter-Done's Avatar
 
Join Date: Dec 2009
Location: TN.
Posts: 70
Re: Q-jet Problems

I just noticed in the picture the secondary butter- flys are Open. They are suppose to be closed at idle and normal driving until loss of vacuum (When You put the Pedal to the Metal). The White diaphragm behind the fuel filter takes care open the rear top flaps when the Throttle is push to the floor. The screw between the Rear Butter-Flys adjusts the manuel linkage. Some thing may be in a bind with this linkage or proper vacuum may not be supplied to operate the diaphragm.
If you check these two things you may find the problem.

Hope this helps
Getter-Done is offline   Reply With Quote
Old 02-09-2017, 12:30 AM   #11
Whitelm
Registered User
 
Join Date: Apr 2014
Location: Idaho Falls, Idaho
Posts: 11
Re: Q-jet Problems

The Float Bowl Insert sits on top of the Power Piston. It appears to that one of it's functions is to keep the spring attached to the needle seat in the proper location. Other than that I don't know what it does. It is item 50 in the attached diagram.
I did notice that the butterflies were slightly opened. After messing with them a bit they seem to stick just barely open on a regular basis. Would this cause such a loss of power when trying to accelerate?
Attached Images
 
Whitelm is offline   Reply With Quote
Old 02-09-2017, 06:24 AM   #12
cadillac_al
Registered User
 
Join Date: Oct 2013
Location: Maine
Posts: 1,412
Re: Q-jet Problems

That secondary air door should have some spring pressure to it and never stick open. I'm surprised they didn't catch that on the 2nd rebuild. I wonder what other simple stuff they missed. It's probably something simple but for now that secondary door needs to be addressed. How's the vacuum?
__________________
76 Chevy K20
76 GMC K15
77 Chevy C10
cadillac_al is offline   Reply With Quote
Old 02-09-2017, 09:28 AM   #13
Dave
DND Trucks
 
Join Date: Dec 1999
Location: NW Indiana
Posts: 1,466
Re: Q-jet Problems

I agree with the above statements regarding the secondary air door. It has to be closed at high vacuum and start to open when vacuum is low. If the air door is open even slightly at high vacuum, it will not make good power.
Now, from the picture and maybe I'm not seeing it but I don't see a vacuum line to the white plastic vacuum pot. Lmk, what you find.

Last edited by Dave; 02-09-2017 at 09:35 PM.
Dave is online now   Reply With Quote
Old 02-09-2017, 10:16 AM   #14
jwilson645
Registered User
 
Join Date: Dec 2011
Location: Morris, Alabama
Posts: 112
Re: Q-jet Problems

Who did you buy it from? Unless it was Cliff's High Performance, then there is no telling what kind of crap parts are in it. Cliff is the expert on Q-jets and provides alot better parts on his rebuilds. Most rebuilt Q-jets are going to be set up generically and unless you have it built specifically for your engine year, size and modifications. I suggest you go over to the forum at www.cliffshighperformance.com and pick up his book on building Quadrajets and read, read, read. They are both a valuable resource on figuring out how these carbs work.
jwilson645 is offline   Reply With Quote
Old 02-10-2017, 08:21 AM   #15
cadillac_al
Registered User
 
Join Date: Oct 2013
Location: Maine
Posts: 1,412
Re: Q-jet Problems

It's true that a lot of rebuilders screw up Qjets and mix and mis-match parts. I hope you saved your original carb for a good back up. In my experience when an engine runs great in park and dies in gear it is often a vacuum leak. I don't see many leak points in your pics but that is always my first thought.

If you plan to dig into your carb or rebuild your old one I can email you Lars Qjet papers if you pm me your email address. Lars doesn't mind sending them out either but it may take a couple days.

I bought a new rebuilt carb from a guy on ebay. He bought it for his Vette and it would not run, falls on its face, got ripped off by I66 Carbs, can't send it back, etc. I bought it pretty cheap and bolted it on my Camaro and it ran perfect out of the box. The Camaro never ever ran so good. Go figure. Same carb two completley different experiences. Sometimes it just ain't the carb so it's hard to figure.
__________________
76 Chevy K20
76 GMC K15
77 Chevy C10
cadillac_al is offline   Reply With Quote
Old 02-10-2017, 10:43 AM   #16
geezer#99
Registered User
 
geezer#99's Avatar
 
Join Date: Aug 2009
Location: Bowser
Posts: 8,888
Re: Q-jet Problems

You mean this info cadillac al.
http://www.digitalcorvettes.com/foru...ad.php?t=88376
geezer#99 is offline   Reply With Quote
Old 02-10-2017, 06:48 PM   #17
cadillac_al
Registered User
 
Join Date: Oct 2013
Location: Maine
Posts: 1,412
Re: Q-jet Problems

That's it Geezer. It only makes sense that it would be a sticky somewhere. I forgot how long it is. I think there is everything a guy needs to know about Qjets. It's a bummer to have to rebuild a new rebuilt carb but that's the way it goes. Since the last guy that took it apart sent it home with the secondary door hanging open who knows what else is wrong. The power piston could be stuck. Is accelerator pump squirting?

This is when it is sooo nice to have another vehicle with a Qjet so you can swap them back and forth to rule out a carb problem or not.
__________________
76 Chevy K20
76 GMC K15
77 Chevy C10
cadillac_al is offline   Reply With Quote
Old 02-10-2017, 09:54 PM   #18
Dead Parrot
Registered User
 
Join Date: Aug 2012
Location: Oklahoma City, OK
Posts: 761
Re: Q-jet Problems

Carb is upside down in both pics.

First pic is a view of the spring your secondary air doors should have to keep them shut.

Second pic shows a lockout lever(don't know the proper name) that yours is missing. It keeps the secondary throttle plates from opening if the choke is closed.
Attached Images
  
Dead Parrot is offline   Reply With Quote
Old 02-17-2017, 08:32 PM   #19
Whitelm
Registered User
 
Join Date: Apr 2014
Location: Idaho Falls, Idaho
Posts: 11
Re: Q-jet Problems

I finally got time to get back to this. I got the secondary butterflies working properly now.
I took time to really feel things out this time around and it would seem that it is starving for fuel rather than flooding. When I put my foot into it at a dead stop (or even a rolling one) it sputters and dies. Vacuum is good. No leaks. The diaphragm is attached to the upper vacuum line in the front and seems to be working like it should. The plunger is also working. I'm starting to think that maybe the float is adjusted wrong, or that maybe the power piston is malfunctioning like was mentioned above. Anybody feel like I'm on the right track??
Whitelm is offline   Reply With Quote
Old 02-17-2017, 11:36 PM   #20
geezer#99
Registered User
 
geezer#99's Avatar
 
Join Date: Aug 2009
Location: Bowser
Posts: 8,888
Re: Q-jet Problems

What's your timing at now?
What did you do to the secondaries?
geezer#99 is offline   Reply With Quote
Old 11-08-2017, 11:30 PM   #21
Whitelm
Registered User
 
Join Date: Apr 2014
Location: Idaho Falls, Idaho
Posts: 11
Re: Q-jet Problems

It has taken awhile for me to get back to this. I advanced the timing to 10 degrees ATD and that helped immensely. I worry about going too far advanced so I stopped there. The engines idles well and it runs ok, but it still seems way underpowered. When I am in the mountains and need to crawl over rocks or go through ruts and stuff like that, much of the time I can't move without putting it into low range. Any ideas?
Whitelm is offline   Reply With Quote
Old 11-08-2017, 11:49 PM   #22
Dead Parrot
Registered User
 
Join Date: Aug 2012
Location: Oklahoma City, OK
Posts: 761
Re: Q-jet Problems

Don't be afraid to try more initial timing. My 350 is at 14. Make sure your vacuum and mechanical advances are working. Most stock motors like more timing then the factory specified. If it isn't pinging on acceleration and is easy to start hot, keep bumping the timing up.

Is your vacuum advance on ported or manifold? Try switching to the other one. Use whichever one works the best.

Total timing(initial + vacuum + mechanical) at about 3000 rpm no load should be about 50 degrees or so. Pretty much out of sight of the timing tab.
Dead Parrot is offline   Reply With Quote
Old 11-09-2017, 02:10 AM   #23
Getter-Done
Registered User
 
Getter-Done's Avatar
 
Join Date: Dec 2009
Location: TN.
Posts: 70
Re: Q-jet Problems

Have you check your mechanical advance in your distributor?
Getter-Done is offline   Reply With Quote
Old 11-09-2017, 03:17 AM   #24
Whitelm
Registered User
 
Join Date: Apr 2014
Location: Idaho Falls, Idaho
Posts: 11
Re: Q-jet Problems

The Distributor is new, (electronic) and the Vacuum advance can is also new. The can is a new stock replacement. I will try advancing it a few more degrees and see what happens.
Whitelm is offline   Reply With Quote
Old 11-09-2017, 02:28 PM   #25
Coley
Senior Member
 
Coley's Avatar
 
Join Date: Oct 2011
Location: Victoria, B.C
Posts: 2,669
Re: Q-jet Problems

I'll weigh in a bit here.
-I fully agree with Geezer, go with at least 2-4 more timing. Unless it starts to ping...you won't have any bad news...just good news. So do this first.
-Next, you say you 'got the secondary butterflies working properly'...did you adjust the spring mechanism that dead parrot has shown in his pic?
This is a very important adjustment for 'balancing' the carbs performance. If you loosen the spring (& tension) off too much the secondaries will open to soon and 'bog' the carb.
If you tighten the spring (& tension) too much, the secondaries will never open and you won't see the engine produce power under load.
As well, that is a newer series carb than what our trucks ran originally. Is the vacuum advance vacuum signal (port) working correctly? ....if you don't advance the timing under load/accel you will have trouble.

Ok...there are a few more things we can check....lets keep going and solve this so start with more timing as Geezer mentioned.
Coley
__________________
....for some men, there is experience, skill and effort....for the others...there is visa and UPS LOL
1966 Chevy 1/2 ton (Florida- Red/white)
1972 Chevy 1/2 ton (California- Blue/white)
2005 Chevy Silverado HD2500/Duramax
2000 Dodge Ram 1500
Coley is online now   Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not 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

Forum Jump


All times are GMT -4. The time now is 04:10 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Copyright 1997-2013 67-72chevytrucks.com