Engine runs poorly - Team Camaro Tech
Troubleshooting Diagnosing problems done here.

 
LinkBack Thread Tools Display Modes
post #1 of 15 (permalink) Old Oct 28th, 02, 06:47 PM Thread Starter
Tech Team
 
Join Date: Oct 2001
Location: IL. Close to St. Louis
Posts: 75
when i start the engine, will idle but when i give it fuel it wants to fall on its face,like someone restricting the exhaust or intake. Not crisp or responsive. every once in a while it will back fire through the carb while giving it gas. I checked the float level and it is ok. dist is ok just got it back from the machine shop. 38 total 12 degree btdc intial (mechanical advance).The eng. is a 283 w/461 heads performer intake holley 600 carb. Any suggestions? Thanks Jason
69RS is offline  
Sponsored Links
Advertisement
 
post #2 of 15 (permalink) Old Oct 28th, 02, 08:37 PM
Senior Tech
 
Join Date: May 2001
Location: Ashby,MN, USA
Posts: 8,305
major vacuum leak? maybe a couple of the plug wires are mixed up- it is easy to mix up numbers 5 and 7, for example.

------------------
1971 Nova(looks like 69 camaro from underneath!)
355sb, vortec heads, HOT cam,T-10 tranny, 3.70 gears 16X8" IROC wheels. 12" Corvette brakes on the way.
see pics here http://community.webshots.com/user/novaderrik
novaderrik is offline  
post #3 of 15 (permalink) Old Oct 29th, 02, 05:35 AM
DjD
Retired
Dennis
 
DjD's Avatar
 
Join Date: Apr 1999
Location: Fortuna, CA
Posts: 26,547
Garage
Sounds like carb adjustment to me. Is the engine completely warm when you have this problem. The accel pump controls the transfer from the idle circuit and may need tuning. also if it's a vac sec carb the secondaries may be opening too soon...

------------------
...Dennis
"The '69, the '96 our local club"
and the "daily driver"
DjD is offline  
 
post #4 of 15 (permalink) Old Oct 29th, 02, 02:13 PM
Gold Lifetime Member
scott
 
Join Date: Mar 2001
Location: alpharetta, GA. 30004
Posts: 191
What kind of carb, what size cfm and what size jets?

------------------
SCOTT
69 RS-SS 396 4-SPEED
scottcleaver is offline  
post #5 of 15 (permalink) Old Oct 29th, 02, 07:15 PM Thread Starter
Tech Team
 
Join Date: Oct 2001
Location: IL. Close to St. Louis
Posts: 75
It's an old Holley 600 DP but a friend rebuilt it for me. Air/fuel mixture is set 1 1/2 turns out. I'm not sure about the jet sizes. It doesn't matter if the engine is warm or cold and it idles fine with no misfires. Could the problem be caused by setting the valves too tight?
Thanks, Jason

[This message has been edited by 69RS (edited 10-29-2002).]

[This message has been edited by 69RS (edited 10-29-2002).]
69RS is offline  
post #6 of 15 (permalink) Old Oct 30th, 02, 01:16 AM
Super Moderator
Bess-68's rule
 
Everett#2390's Avatar
 
Join Date: Sep 2000
Location: Va Beach VA
Posts: 32,175
Garage
I would suggest ot set the idle with a vacuum gauge and adjust for the highest reading.

Look down the throttle bores and see if fuel is coming from the venturi boosters. If it is, then lower fuel level.

You're looking for the throttle plates to be closed so as the plates uncover some of the idle transfer slots. This way will provide a better transition from idle to the main feed system.

As Dennis suggested, check accel pump adjustments. For every minute movement of the throttle, the same should be happening with the fuel pump. This should get you going with cruising, but, for WOT from idle, a dbl pumper is too much.

If you still have an off-idle stumble, increase the squirter size by three numbers. Say you started at 25, install a 28, etc. until it clears up. Some times a swap from the front to rear squirters assists in troubleshooting. There is a hollow screw for the squirter to buy. This helps alot, I don't know why Holley doesn't install it as standard equipment. Holley PN 26-12.

Make sure your friend didn't forget the ball underneath the squirter and the rubber check valve in the fuel bowl for the accel pump.

If you're trying to go from idle to WOT, it won't happen very well with a dbl pumper. TOO much fuel at one time. One can tune engine by ear, and maybe make it work, but, usually a dbl pumper dumps soo much fuel, it overloads. One has to work up the rpm's for a dbl pumper to be good, say start at 2500 rpm.

You're not running a tunnel ram on top are ya?

------------------
Everett "OBJECTS IN THE MIRROR DISAPPEAR UPON RAPID ACCELERATION"
Everett#2390 is offline  
post #7 of 15 (permalink) Old Oct 30th, 02, 05:53 AM Thread Starter
Tech Team
 
Join Date: Oct 2001
Location: IL. Close to St. Louis
Posts: 75
I will try to fine tune the carb or maybe switch with a known good one. Thanks for the replies. Will let you know on what I find.

Jason
69RS is offline  
post #8 of 15 (permalink) Old Oct 30th, 02, 06:10 AM
DjD
Retired
Dennis
 
DjD's Avatar
 
Join Date: Apr 1999
Location: Fortuna, CA
Posts: 26,547
Garage
Check this thread out https://www.camaros.net/forum/Forum9/HTML/008656.html for accl pump and squiter info. Of you go to a larger squiter you may require a pump cam change as well. The larger squiter opening allows the pump shot to be more (all at once) volume and what you may need is more duration.

I think Everett meant to say adjust the idle mixture screws for most vacuum not the idle. It will have an effect on the idle as vacuum goes up so will the rpms

------------------
...Dennis
"The '69, the '96 our local club"
and the "daily driver"
DjD is offline  
post #9 of 15 (permalink) Old Oct 31st, 02, 12:52 AM
Super Moderator
Bess-68's rule
 
Everett#2390's Avatar
 
Join Date: Sep 2000
Location: Va Beach VA
Posts: 32,175
Garage
Thanks Dennis for picking up the missed word(s).

I'll pass it on from experience, when pump cams are needed when the squirter size has been increased, the engine will start to come up in rpms, but, then will stumble. The pump shot was too short, thus, the main system did not come into play yet. Therefore, the larger squirter to eliminate the bog, the cam to provide enough fuel to carry over until the main circuit kicks into play.

Everett
Everett#2390 is offline  
post #10 of 15 (permalink) Old Nov 2nd, 02, 04:15 PM
Senior Tech
 
Join Date: Mar 2002
Location: Austin, TX, USA
Posts: 5,277
All very good suggestions. Just wanted to add one more. Depending on the cam your running (actually idle vacuum), you may have to open the primaries up too far to get it to idle good. As a result, the primaries are almost out of the idle circuit and don't provide a transition to the main circuit. The accellerator pump will help considerably, so follow the advice given here by others first.

What I wanted to add is that holley 4150 / 4160 carbs (and others I expect) have a stop screw for the secondaries located near the secondary shaft on the passenger's side. This stop cracks the secondary throttle plates open slightly to allow air to bypass and also prevent the butterfly from sticking in the bore. I've seen two different recommendations for adjusting this screw. One is to back the screw out (carb removed) until the secondary plate just closes. Then tighten the screw 1/4 turn. The other procedure is the same but says 1 full turn. In any event, check the adjustment. If it is set approximately between 1/4 and 1 turn from contacting the stop, try opening it up another half turn and reset the idle circuit. You'll probably have to richen the idle circuit slightly - use the vacuum gage method to adjust. This will allow you to back off the idle speed screw on the primaries and get the primaries back into the idle circuit again. Unfortunately, any time you need to adjust this screw, it means removing the carberator.

It's a good idea to check this adjustment but whether or not you'll need to increase the secondary stop opening depends on cam / idle vacuum, and how well sized the carb is for the motor.

-dnult
dnult is offline  
post #11 of 15 (permalink) Old Nov 2nd, 02, 07:38 PM
Senior Tech
Rob
 
Join Date: Nov 2002
Location: ontario canada
Posts: 355
dont over look the power valve,my 68 396bb 4spd novass did it twice to me.my engine had the big stumble/hesitation from idle to about half throttle and then the big poof of fire thru the carb,and it was rebuilt.any way it worked for me, holley sells replacements that are gauranteed aginst this from happening. hope this helps.
late68 is offline  
post #12 of 15 (permalink) Old Nov 3rd, 02, 06:55 AM
Senior Tech
 
Join Date: Mar 2002
Location: Austin, TX, USA
Posts: 5,277
I just installed one of those blow-out protectors. It is a little check ball assembly. You must remove the base plate, then partially drill out the passage that feeds the power valve. The check assembly is then tapped in flush with the base. It's better to do this during a rebuild because the base gasket can tend to stick and make a mess which isn't easy to clean up. A fresh rebuild would probably be Ok. The only hitch is that the kit only comes with one check-ball assembly. Some carbs with two power valves will require two kits.

-dnult
dnult is offline  
post #13 of 15 (permalink) Old Nov 3rd, 02, 07:14 AM
DjD
Retired
Dennis
 
DjD's Avatar
 
Join Date: Apr 1999
Location: Fortuna, CA
Posts: 26,547
Garage
I have not seen blow proof power valves but just installed Holley's P/N 125-500 Power Valve Check Ball Kit in my 780 with 2 power valves. This kit came with the drill and drill stop, 2 balls, 2 springs and 2 washers that you tap in to keep everything in place.

69RS have you gotten this worked out?
DjD is offline  
post #14 of 15 (permalink) Old Nov 3rd, 02, 05:53 PM Thread Starter
Tech Team
 
Join Date: Oct 2001
Location: IL. Close to St. Louis
Posts: 75
Thanks for all the replies. I still haven't figured out the problem. When the car was idling, I adjusted the air fuel mixture on both sides and there was no change in the RPMs. I think it might be in the carb itself. I am going to borrow my friends carb, which I know is good, and see if it runs better. I will update you when I find out.

Jason
69RS is offline  
post #15 of 15 (permalink) Old Nov 4th, 02, 01:12 PM
Senior Tech
 
Join Date: Mar 2002
Location: Austin, TX, USA
Posts: 5,277
Problem with spare parts is that you can't be certain of their condition or that they are properly set up for your engine. You may very well find yourself chasing another problem. Several good suggestions have been offered here - why not give them a try? Also, while you have the fuel bowls off, write down the jet sizes so if you decide to re-jet, you'll know where to start without tearing into it again. If you're running a holley, you best get familiar with it because you'll probably be messing with it again someday.

-dnult
dnult 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