Idle problems???Possible bad carb?? - Team Camaro Tech
Tech 2002 General Tech questions from 2002
Replies ONLY, no new topics.

 
LinkBack Thread Tools Display Modes
post #1 of 12 (permalink) Old Jun 26th, 02, 08:44 AM Thread Starter
Senior Tech
 
Join Date: May 2001
Location: Mass
Posts: 252
I just finished replacing a set of heads on my SBC..Went to 64cc trick flows(Orig 76cc chevy heads)..It starts and revs fine and clean..But the idle is sporatic...I have drilled the butterflies. clipped the primary springs, and changed the metering rod...Still the idle is poor..If I rev it it spins up nice but on the way down it like hangs up at 1500rpm then slowly drops down to 700rpm...I adjust the carb again idle at 1000rpm..rev it up and again it hangs monetarily at 1500 then drops down to 700rpm... I can't get idle adjustment screws to make a difference either..
I am running along duration cam [email protected] and 515 lift..The carb is a edelbrock 600, victor Jr intake, trick flow 23* heads 64cc, on a SBC 355 with flat tops ..

I have rebuilt the carb,,I have adjusted the valves 3 times...The timing is at 20 Base..I am pulling 4-5"vacuum(I use to pull 7-8" before the head change)..I have looked everywhere for a vacuum leak...(Used starting fluid) at 2000 rpm the vacuum is solid at 13"...So I don't believe there is a vacuum leak...

I am leaning towards a carburation problem..Anyone have any thoughts on this?? Any help would be greatly appreciated..Thank you



------------------
Restored 68 Camaro R/S 327 4 speed
-------------------------
Restored 55 chevy Belair
Blown, Fuel Injected
http://community.webshots.com/user/badcaiman
-------------------------
Badcaiman is offline  
Sponsored Links
Advertisement
 
post #2 of 12 (permalink) Old Jun 26th, 02, 09:38 AM
Gold Lifetime Member
Jody
 
camcojb's Avatar
 
Join Date: Jan 2000
Location: Wilton, Ca. USA
Posts: 10,073
I really prefer a Holley carb (HP series are nice) or a Demon on an engine like yours, especially with that size of a cam. The Edelbrock is a nice cam on mild engines. I just never was satisfied with how it worked when you get into a large camshaft. Any of your friends have a Holley you could borrow just to try?

Jody
camcojb is offline  
post #3 of 12 (permalink) Old Jun 26th, 02, 01:48 PM Thread Starter
Senior Tech
 
Join Date: May 2001
Location: Mass
Posts: 252
Called Lunati Tech today..They tell me 4-5" of vacuum is about right for my cam..And that idle should be somewhere between 1200 1500rpm...That sound way to high..Anyone have any thoughts on this..Thanks Again

------------------
Restored 68 Camaro R/S 327 4 speed
-------------------------
Restored 55 chevy Belair
Blown, Fuel Injected
http://community.webshots.com/user/badcaiman
-------------------------
Badcaiman is offline  
 
post #4 of 12 (permalink) Old Jun 26th, 02, 01:58 PM
Team Member
John
 
JohnZ's Avatar
 
Join Date: Sep 2000
Location: Washington, Michigan USA
Posts: 7,728
I wouldn't expect any more vacuum or any better idle than you've got - when you use that radical a cam and single-plane intake, you're not going to get a normal "street" idle. May look great in a magazine buildup article with a 5-second-long dyno pull, but most of that stuff is junk for street driving.

------------------
JohnZ
CRG
'69 Z28 Fathom Green
JohnZ is offline  
post #5 of 12 (permalink) Old Jun 26th, 02, 02:07 PM Thread Starter
Senior Tech
 
Join Date: May 2001
Location: Mass
Posts: 252
Live and learn I guess...But with the old heads I could get a reasonable idle...Was hoping that the head change would just help things..But I can tell you this It sings above 2000 all the way up to 5500...

------------------
Restored 68 Camaro R/S 327 4 speed
-------------------------
Restored 55 chevy Belair
Blown, Fuel Injected
http://community.webshots.com/user/badcaiman
-------------------------
Badcaiman is offline  
post #6 of 12 (permalink) Old Jun 29th, 02, 04:49 PM Thread Starter
Senior Tech
 
Join Date: May 2001
Location: Mass
Posts: 252
If I rev it it spins up nice but on the way down it like hangs up at 1500rpm then slowly drops down to 700rpm...I adjust the carb again idle at 1000rpm..rev it up and again it hangs monetarily at 1500 then drops down to 700rpm..The idle mixture screws have no effect..
Anyone have any thoughts on this..Is this in fact a carb problem or am I missing a vacuum leak..I have sprayed starting fluid everywhere..No change in idle speed..The vacuum gauge holds steady when I accelerate and hold the rpm at 2000(at 700 rpm it moves between 4-5").It almost seems like it starts to load up and drops the rpm...Any thoughts before I spend the cash on the new carb..

Thank you

------------------
Restored 68 Camaro R/S 327 4 speed
-------------------------
Restored 55 chevy Belair
Blown, Fuel Injected
http://community.webshots.com/user/badcaiman
-------------------------
76 Limited edition T/A # matching
-------------------------
26 Ford Roadster..Pro street
-------------------------
79 Corvette..Frame off restoration..
Badcaiman is offline  
post #7 of 12 (permalink) Old Jun 30th, 02, 12:38 AM
Senior Tech
Mark
 
Join Date: Feb 2002
Location: LR AR
Posts: 2,372
What kind of fuel are you using? What temperature do you get at full operating temp? Does it happen right away or after a log drive? What does your ignition curve look like? 20 degrees initial!?!? How much do you have in the distributor?

-Mark.
stingr69 is offline  
post #8 of 12 (permalink) Old Jun 30th, 02, 02:06 AM
Senior Tech
 
Join Date: Aug 2000
Location: DULUTH, GA.
Posts: 917
What have you been doing to the carB? Why did you drill the butterflys and clip the springs? There are calibration kits available for these to allow for spring/rod changes without permanent changes. Rods and springs do not affect the idle circuit of these carbs.

The Edelbrock carbs are the easiest to tune, most reliable, most stable and best metering carbs on earth. I have used them all, Holleys, Demons etc. and you should be able to get the Edel going perfectly. And, no gas line on gaskets! No leaks, drips or runs. I have used these carbs with a wide variety of cams.

I have a XE274 and the best idle I can get is round 1000. That's a 234ish at 50 cam. So yours is in line.

The mixture screws are not working because you are running on primaries. When you drilled the butterflies, if that is putting holes in the primary butterflies, then the air bled thru the holes may be the problem.

Idles that do not snap back and kinda run down as opposed to return to there idle rpm are too lean in general. Generally, you have to get less than 1000rpms to work on the idle circuits of unmodified AFB carbs.

Another carb may work better for you, but I assure you that the AFBs will work as good as any other when tuned correctly.

Even tho I have not been too specific, I hope some of this turns gears for you.

Go to http://www.edelbrock.com/automotive/eps_intro.html for more information on Edelbrocks if you do not have a complete manual.



------------------
STEVE JACK
ConceptOne Pulleys and Brackets

Northern/Southern Rodder Magazine's "Jack'Stands" author and creator
Techical forum/links at www.inccn.net/techforum.htm
HOTRODSRJ is offline  
post #9 of 12 (permalink) Old Jun 30th, 02, 10:52 AM Thread Starter
Senior Tech
 
Join Date: May 2001
Location: Mass
Posts: 252
HOTRODSRJ & stingr69
Thanks for the reply...I drilled the butterflies because it was recommended..to get more air into the engine without having to open the primaries so much that I leave the idle circuit..And the reason I clipped the spring on the metering rods was that the lowest spring they make for the edelbrock is blue(5"vacuum..I run about 4-5" with my cam)and with the blue I was still getting dribble out of the primaries...

The rpms hanging happens all the time after It warms up..(Won't idle cold)..Set the rpm at 1000-1200...holds steady rev it up (revs great) on the way down hangs for a bit at 1500-1700rpm then comes down to 700rpm..If I crack the throttle again same thing happens..Hotrodsrj..do you believe this is a leaning out condition..I was thinking to rich...I have tried letting the idle drop to 500-600rpm and work with the idle mixture screws but they still don't respond..and if I crack the throttle the linkage comes back and the primaries continue to dribble...

I run super unleaded and the temp while driving stays about 180-190(210-220 at idle)..
I have 20* base timing with 38* all coming in by about 3000rpm..

Do you guys think a Holley with a 4 corner idle would help...
Thank you

------------------
Restored 68 Camaro R/S 327 4 speed
-------------------------
Restored 55 chevy Belair
Blown, Fuel Injected
http://community.webshots.com/user/badcaiman
-------------------------
76 Limited edition T/A # matching
-------------------------
26 Ford Roadster..Pro street
-------------------------
79 Corvette..Frame off restoration..
Badcaiman is offline  
post #10 of 12 (permalink) Old Jun 30th, 02, 11:40 AM
Senior Tech
Mark
 
Join Date: Feb 2002
Location: LR AR
Posts: 2,372
I like Jody's idea of borrowing a carb from a buddy before laying down the hard cash but if that is not feasable, get a SIMPLE carb and see how it works. If it turns out to not be the issue I guess Ebay could ease the pain with disposal but I just hate to solve problems that way.

A new carb might be worth a try.

-Mark.
stingr69 is offline  
post #11 of 12 (permalink) Old Jun 30th, 02, 12:25 PM
Senior Tech
Eric
 
Join Date: Dec 2000
Location: Kentwood, MI
Posts: 8,097
Definately try a different carb, preferably a Holley. If your idle adjustment screws are not affecting anything you are definately not running on the idle circuit - you are idling on the main jets.

Another thing to check is your mechanical advance mechanism. I have a stock type HEI on my 383 and the mechanism will get hung up once in a while and my advance curve "gets funky." I clean the weights and change the little plastic bushings once a year just to be safe. A sticking advance mechanism could easily cause the slow return to idle speed.

Eric68 is offline  
post #12 of 12 (permalink) Old Jun 30th, 02, 12:37 PM
Senior Tech
 
Join Date: Aug 2000
Location: DULUTH, GA.
Posts: 917
If it won't idle when cold then it's definitely not rich. The cold condtion tells me that the density of the cold air makes it more lean and that's why it won't idle cold. If it where rich, it would idle better cold.

I would recheck the idle circuit. Fill the holes with screws and see if you can get the idle to change with mixture screws.

Another proven carb may help, but the one you have should work too. Four corner idle with large cams in my book are the hardest to set without plug fouling and gassy smelling exhaust. The Road Demon on my 69 has great throttle response and so forth, the idle took me several weeks to get it right and it still is a smiggin rich. But, it will idle good with the XE274.

Try another carb, but the one you have should work if tuned properly. The "dribble" doesn't sound right at all. Another thought about timing etal and fuel pressure. Make sure the fuel is not over 6lbs. I also don't think you need 20 degrees of initial advance and this could be affecting your carb. Set it at 14 and try to get the idle circuit first in play. Then if it works, come back and play with total. If you have too much initial timing, you can have problems achieving this idle...I have run into this before. I bet it can be done, try it.

------------------
STEVE JACK
ConceptOne Pulleys and Brackets

Northern/Southern Rodder Magazine's "Jack'Stands" author and creator
Techical forum/links at www.inccn.net/techforum.htm
HOTRODSRJ 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 not 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