Carb Experts Help - Team Camaro Tech
Engine General Engine Discussion.

 
LinkBack Thread Tools Display Modes
post #1 of 10 (permalink) Old Mar 21st, 11, 08:14 AM Thread Starter
Senior Tech
Mark
 
Join Date: Sep 2006
Location: Bellmore, Long Island
Posts: 1,033
Carb Experts Help

Looking for some help to what I think is a carb problem. The carb is a 1969 Quadrajet (7029203). After the car sits for a day when I go to restart it it takes quite a bit of pumping the pedal and cranking to start. Similar to what you would expect after a car had been sitting for a long period of time. Once started it will run for 4-5 seconds then stall, does this 2-3 times then starts and runs fine once warm.

The carb was restored years ago and never used until last year and has had this problem since intalled.

Any ideas if this sounds like a carb problem?

1969 Camaro SS
350/300 M20
12 Bolt 3:73 Posi

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Myfirst 69SS is offline  
Sponsored Links
Advertisement
 
post #2 of 10 (permalink) Old Mar 21st, 11, 09:15 AM
Gold Lifetime Member
John
 
Vintage 68's Avatar
 
Join Date: Mar 2002
Location: Moraga,Ca.,USA
Posts: 13,705
Re: Carb Experts Help

First thing to check would be the Choke circuit, when cold - is the choke blade closing when you step all the way down on the pedal first time?
(hopefully most realize on older choke equiped cars, you need to 'Set' the choke system by stepping all the way down on the throttle once before trying to crank the starter ...)

Next, is the fuel bowl retaining fuel after long periods of no-use.
Rochester Q-Jets had a bad habit of the main fuel jet plugs in the base of the fuel bowl coming loose or the seal cracking and they'd leak the fuel out of the bowl over a period of time.
The 'fix' is to epoxy the plugs back in place. This requires removal of the carb. and taking the bottom throttle plate off to gain access to them.
Here's a bowl that has had the plugs epoxied - Click image for larger version

Name:	Rochester Q.Jet Fuel bowl plugs with Epoxy fix.jpg
Views:	95
Size:	46.2 KB
ID:	21319

If none of above are the problem, here are a couple other items to check;
1.) Does the fuel pump have a bad 'check-valve' - allowing the fuel to drain back to tank level?
2.) Along with above - the correct carb. inlet fuel filter should have an "Anti-drainback" Check valve built into the rubber seal on the end - GM released these modified fitlers in the 70's to combat the drain back issues.
3.) Has the accelerator pump seal (often called the 'Umbrella') shrunk up over the years and is preventing a good pump shot for starting? (note: this can be more common if the carb has sat around for a time drained or if the fuel bowls are leaking-down and the car sits for long periods, this tends to dry-out the seal.)

Hope this helps

1968 Convertible
Some trucks
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Other V8 things - some of which float
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Other V6 things - none of which float
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Oh yeah, and 1 "Straight-Six" ...
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


If a man says something in the garage - and his wife can't hear him - is he still wrong !!!
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Vintage 68 is offline  
post #3 of 10 (permalink) Old Mar 21st, 11, 09:35 AM
Senior Tech
alex
 
Join Date: Nov 2010
Location: boston ma.
Posts: 854
Re: Carb Experts Help

Mark. The first thing to check is your fuel pump for pressure and volume or flow. Now getting to the Quadrajet more than likely you have more than one problem here. First has the carb ever been rebuilt after a couple of yrs the gaskets get old and dry the air bleeds get clogged with fuel gum and varnish etc. The carb very well could need a refresh. Next on the list Rochester,sare notorios for the main well,s leaking down overnight causig allthat crankin because ther,s no fuel in the bowl. Standard igniton used to sell a little rubber gasket to cure this prblem and it was anok fix while the gasket was pliable but after a while engine heat shrunk the gasket and your back to sqare one . Here is my cure for the wells . When the carb is apart and clean flip over the main body with a small hammer tap lightly on the lead joints at the bottom to set them in a bit . N O T I C E I said tap lightly or you wil ruin the carb . Mix up some epoxy that will take heat and epoxy up the wells nice and neat smear the sides a bit for complete coverage. let it dry finnish your rebuild and your good to go.That should take care of your problem. Cheap laquer thinner is a good carb cleaning solvent to soak the parts in make shure you blow out every little hole out and you will be fine.Hope this helps.ALEX
ss27 is offline  
 
post #4 of 10 (permalink) Old Mar 21st, 11, 09:47 AM
Gold Lifetime Member
Tom
 
Join Date: Mar 2008
Location: the 02176
Posts: 5,985
Re: Carb Experts Help

Good suggestions above.

To troubleshoot, when the car is cold, after sitting, take a look down the primaries while holding the choke butterfly open. Open the primaries by hand to see if you get a good strong pump shot or not. If so, have somebody else start the car while you observe the operation of the butterfly plate. Too far open, too far closed?
Manipulate it with your hand to see what makes the car run better and you will see what it needs.

'67 rs - ordered new by my Grandfather
327 L30, K-K, Deluxe int, tach & gauges, 12 bolt posi, 4 speed.

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
-
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Melrose RS is offline  
post #5 of 10 (permalink) Old Mar 21st, 11, 02:05 PM Thread Starter
Senior Tech
Mark
 
Join Date: Sep 2006
Location: Bellmore, Long Island
Posts: 1,033
Re: Carb Experts Help

So I checked a few things mentioned above. First I pulled the throttle all the back and noted position off choke blade, it wasn't closed all the way. Then I held it open while looking to see if I was getting pump of gas when the throttle was pulled back the second time and I did. I stopped there and checked my divorced choke to make sure it was not hung up on anything, seemed good. I undid the clip that attches the rod to the choke blade (not the one off the thermospring to carb) the one at the top and bent that slightly and reattached. Rechecked it and now the choke blade is fully closed when cold. Got in the car turned the key and it started right up. Will try again tomorrow to see if that solved the problem. Hopefully all this makes sense.

1969 Camaro SS
350/300 M20
12 Bolt 3:73 Posi

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Myfirst 69SS is offline  
post #6 of 10 (permalink) Old Mar 21st, 11, 03:36 PM
Gold Lifetime Member
Tom
 
Join Date: Mar 2008
Location: the 02176
Posts: 5,985
Re: Carb Experts Help

Makes sense. Should help. Good luck.

'67 rs - ordered new by my Grandfather
327 L30, K-K, Deluxe int, tach & gauges, 12 bolt posi, 4 speed.

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
-
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Melrose RS is offline  
post #7 of 10 (permalink) Old Mar 21st, 11, 06:28 PM
Super Moderator
Bess-68's rule
 
Everett#2390's Avatar
 
Join Date: Sep 2000
Location: Va Beach VA
Posts: 31,769
Garage
Re: Carb Experts Help

As directed, you're on the right path. You have not mentioned the intake manifold the carb is mounted upon.
If an OE cast iron, the manifold will have the crossover path and with a working heat riser valve on the pass exhaust manifold, the heat will travel through the manifold to aid in heating of the bimetal choke spring to open the choke plate faster. The choke pull-off, the white diaphram cannister on the pass front side of the carb, pulls against the bimetal spring opening the choke. Also, the heat passing through the manifold would heat the carb to prevent icing of the gasoline in cold weather.

If you have an aftermarket dual plane manifold, there is a crossover, but nothing to heat the carb. If you have tubular headers, there is no heat riser and choke plate stays closed a little longer.

In summary, you are on the right track.

Give a man a rescued dog for the health of both their souls. May 2017 ROTM Winner - Thank you!
'
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
CUBS - 2016 World Series Champions - Thank you, Joe Madden enjoy your next chapter.
Everett#2390 is offline  
post #8 of 10 (permalink) Old Mar 21st, 11, 07:00 PM Thread Starter
Senior Tech
Mark
 
Join Date: Sep 2006
Location: Bellmore, Long Island
Posts: 1,033
Re: Carb Experts Help

Stock manifolds with heat riser valve removed, Performer manifold with crossover path blocked.

1969 Camaro SS
350/300 M20
12 Bolt 3:73 Posi

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Myfirst 69SS is offline  
post #9 of 10 (permalink) Old Mar 21st, 11, 07:14 PM
Super Moderator
Bess-68's rule
 
Everett#2390's Avatar
 
Join Date: Sep 2000
Location: Va Beach VA
Posts: 31,769
Garage
Re: Carb Experts Help

Keep taking the path you're on, you'll get there. It can be made to work.

Give a man a rescued dog for the health of both their souls. May 2017 ROTM Winner - Thank you!
'
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
CUBS - 2016 World Series Champions - Thank you, Joe Madden enjoy your next chapter.
Everett#2390 is offline  
post #10 of 10 (permalink) Old Mar 21st, 11, 10:01 PM
Senior Tech
Wes
 
Join Date: Dec 2003
Location: Leander, TX
Posts: 2,762
Re: Carb Experts Help

Quote:
Originally Posted by Myfirst 69SS View Post
Looking for some help to what I think is a carb problem. The carb is a 1969 Quadrajet (7029203). After the car sits for a day when I go to restart it it takes quite a bit of pumping the pedal and cranking to start. Similar to what you would expect after a car had been sitting for a long period of time. Once started it will run for 4-5 seconds then stall, does this 2-3 times then starts and runs fine once warm.

The carb was restored years ago and never used until last year and has had this problem since intalled.

Any ideas if this sounds like a carb problem?
Quite simply, the fuel in the carb is evaporating. To prove it, do this. Just before you fire it up tomorrow, pour an ounce of fuel directly into the primaries and pour another ounce into the fuel bowl through the little vent tube (the little 3/8" tube that points up). You'll need a little squirt bottle or tiny funnel.

She'll fire right up.

Today's fuel, especially with the stupid ethanol (thanks to your friends at Archer Daniels and their lobbyists), has an evaporation rate that is MUCH more rapid than gasoline of yesteryear.

In today's cars, it's not a problem because their fuel systems (FI) are completely closed off to the atmosphere. No so on our old rigs with carburetors.

Still don't believe it?

Pour an ounce of fuel into a small container. Mark on the container where the fuel is. Let sit on your workbench for 24 hours. Then check how much of your one ounce is left. And this loss took place without engine heat to spur it on.

Holley carbs are less prone to this hard-start problem because their fuel bowls are much larger.
Straight-line-69 is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Team Camaro Tech forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
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.
NOTE we receive a lot of registrations with bad email addresses. IF you do not receive your confirmation email you will not be able to post. contact support and we will try and help.
Be sure you enter a valid email address and check your spam folder as well.



Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



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

 
For the best viewing experience please update your browser to Google Chrome