Tuning a Holley 650 - Team Camaro Tech
Troubleshooting Diagnosing problems done here.

 
LinkBack Thread Tools Display Modes
post #1 of 5 (permalink) Old Feb 11th, 07, 01:51 PM Thread Starter
Senior Tech
 
Join Date: Jan 2007
Location: S.F Bay Area
Posts: 652
Tuning a Holley 650

I just bought my 67 and don't know much about the car. When ever I floor it the carb bogged down like it was starving for fuel. When I lift off the gas a little it catches up with RPM and runs great.
The mechanic who was hanging around when I bought the car told me to go up two jet sizes on front of the carb.
I figured the problem was in the secondary but this guy owns a fairly large auto service place and told me to do that first.
I changed the jets from 70 to 72 and sure enough it runs like a bat out of hell BUT, from idle to 2000 RPM it has a studder now.
After the studder it runs sweet.

Could this just an air fuel screw adjustment or what?

Any help would be greatly appreciated.

Rich

AFR Heads W/ Jesel valve train

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

67 RS / SS

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Rich-Allen is offline  
Sponsored Links
Advertisement
 
post #2 of 5 (permalink) Old Feb 11th, 07, 02:35 PM
Gold Lifetime Member
Harry
 
dawg's Avatar
 
Join Date: Mar 2004
Location: Colebrook CT.
Posts: 4,017
Re: Tuning a Holley 650

sounds like pump shot to me.
go up to the next number on the pumpshot cam.
Off Idle Hesitation: Is one the most common problems w/carbs especially when used on modified engines. If you experience an off idle stumble as soon as you accelerate from part throttle or idle check the distributor first for correct initial timing & a proper mechanical advance curve. (inadequate timing will also cause a backfire through the carb under acceleration). First check the pump circuit to make sure that the squirter produces fuel as soon as you move the throttle. If not make sure your linkage is set properly (there should be no play between pump arm and pump linkage at idle), then if you have no pump shot trace the pump circuit back to locate the problem. Then check front & rear float levels for proper setting (too low of a fuel level in bowl will delay main circuit startup). Next move to the carb idle circuit. Most of these type stumbles occur because of a lean idle & transition circuit especially w/ large manifolds, lots of cam timing, and little or no manifold vacuum. First check to make sure the primary throttle plates @ curb idle arenít too far up into the transition slot reducing fuel enrichment when you fan the throttle. If the throttle blades are more than about .04Ē into the transition slot either open the secondary throttles to put more air in the motor or drill a hole in each primary throttle plate on the bowl side to increase idle air. Start w/ about .09Ē holes in the plates. If you still have a stumble adjust the idle mixture screws about 1 turn richer from best idle & see if this cures the problem. If this helps you can bet the idle circuit is too lean. A good indication of a lean idle is if your idle mixture screws are out @ best idle over 2 turns, or you can just bump the accelerator pump arm @ idle & the idle smoothes out. In some cases richening the main jets by a couple of #ís will richen the idle enough since the idle circuit pulls fuel from the main circuit. If your main circuit is already tuned this can be a mistake. If you need to richen the idle circuit the best method is to increase the idle feed restriction about .002Ē @ a time. This should remedy the situation or reduce the idle air bleeds by about .005" at a time.
Full Throttle Hesitation: You should now have your idle & transition circuits tuned up and should proceed with the pump circuit if under hard launches you get a stumble. In most cases your not supplying enough fuel when you whack the throttle & manifold vacuum drops before you can start the main circuit. This causes a lean spot you need to cover up w/ the pump circuit. Usually going up on squirter size a few thousands will cure the problem. When you go above .035Ē squirter size you should install high flow pump screws so you donít limit fuel flow (AED #5550) If you fix the initial stumble and then after the car moves alittle, it becomes lazy you are running out of pump shot too early. You can change pump cams to a higher lift cam (AED #5560) or youíll have to add a 50cc pump kit (AED #5565 ). This is especially helpful when you are using a large carb that has a slow starting main circuit, or have a heavy car, or a tight converter. One thing to remember is that you only want enough pump shot to cover the lean hole in the fuel delivery curve, any more can make the car lazy. Another major problem on hard accelerating drag cars is when the car gets out almost through low gear & then noses over. This is caused by fuel rushing to the back of the rear bowl under high G forces uncovering the rear jets. The purchase of our #5895 stainless jet extension kit will solve this problem. We also offer special machined and weighted floats for additional protection with our custom brass jet extensions included. (AED #5896)
Flooding & Hard Starting Hot: When you have fuel dripping out of the boosters or a very rich condition @ idle, first check front & rear float levels. Remove both sight plugs (AED #5170) clear sight plugs are safer,easier, & inexpensive w/ motor off & make sure fuel in the bowls is even with or 1/3 up from the bottom of sight hole. If too high adjust down (clockwise) w/ needle & seat nut and recheck. If you still canít get the float level down check for heavy float or trash in needle & seat. Holley carbs hate trash & water! With floats set if you still experience flooding tighten fuel bowls (incorrect seal between metering block and main body can cause booster pull-over) or check for mainbody and metering block flatness. We are assuming you have checked fuel pressure (AED gauge #6100) and itís less than 8 psi running. If you still have a problem a blown power valve will cause an excessively rich idle, vacuum check it or replace. Always use a carb heat shield or insulated carburetor spacer if you have an aluminum intake because of the excessive heat bled off to the float bowls. This will cause fuel bowl over, percolation, & vapor lock resulting in hard starting & spongy throttle response. We manufacture a complete line of heat insulating Birchwood Spacers in 1/2" and 1" (#'s 6150 thru 6173) for all applications.
*** Special note about metering block gaskets since about midway 2004. The gasket material has been changed from the original Holley material used for decades! Some are harder & some are softer. Always re-tighten bowl screws after initial use as the mating surface between the metering block & main body surface is critical in proper carburetor operation! I would not reuse metering block gaskets, they are inexpensive so just replace them. If you have a strange problem with idle or cruise your first step should be to replace the metering gaskets. We have seen allot of this in the past year with virtually everyone's gaskets. Are latest gaskets (as of March 2005) are the best out there, but I would still replace them on any carburetor disassembly.


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

434 stroker
US Navy retired

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
dawg is offline  
post #3 of 5 (permalink) Old Feb 12th, 07, 05:02 AM Thread Starter
Senior Tech
 
Join Date: Jan 2007
Location: S.F Bay Area
Posts: 652
Re: Tuning a Holley 650

Thank you for the post!

The car ran awesome on the low end before I changed the jets. Which made me think I should go back to what I had before and go up on the secondary side.

I will begin eliminating the problem as you mentioned today after work.

Thanks again.

Rich

AFR Heads W/ Jesel valve train

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

67 RS / SS

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Rich-Allen is offline  
 
post #4 of 5 (permalink) Old Feb 12th, 07, 06:34 AM
Super Moderator
Bess-68's rule
 
Everett#2390's Avatar
 
Join Date: Sep 2000
Location: Va Beach VA
Posts: 31,584
Garage
Re: Tuning a Holley 650

Quote:
Originally Posted by Rich-Allen View Post
The car ran awesome on the low end before I changed the jets. Which made me think I should go back to what I had before and go up on the secondary side.
Working on the secondary side does nothing for an off-idle stumble.

A said by the post, initial timing has alot to do with stumble. I'd advance the initial to say 10-12* BTDC and view/listen/feel the results. If engine reacts better, going in the right direction. If not, then up fuel squirter size. Replace fuel squirter screw for a hollow screw regardless.

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 - maybe this year, 2019 ...
Everett#2390 is offline  
post #5 of 5 (permalink) Old Feb 13th, 07, 10:56 AM
Senior Tech
 
Join Date: Mar 2002
Location: Austin, TX, USA
Posts: 5,277
Re: Tuning a Holley 650

Does the carb have vacuum operated secondaries or mechanical? If the former, the secondary spring is probably too soft. If the later, the behavior you described is somewhat expected if you have an automatic transmission.

Dawg's post has some good info in it. I'd also recommend you check out the tech reference documents from the home page of this site. I think it's Series II where DJD et. al. have created some helpful documents about the care and feeding of Holly carbs.

Dave
========================
68 Coupe, 350 w/ Edelbrock Performer RPM heads, cam, intake, 700R4, Dave's small body HEI
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



Similar Threads
Thread Thread Starter Forum Replies Last Post
What is your favorite Brand? 69camarofast Bench Racing 20 Sep 16th, 06 10:53 PM
4500 dominator flange compatible with 650 holley? 67stang Engine 7 Nov 13th, 05 05:39 AM
Holley Tuning. dtm1968 Engine 1 Oct 10th, 05 06:31 PM
Any chance a 650 CFM Holley spreadbore will feed my big block?? Eric Kammerer Performance 9 Aug 5th, 05 07:45 PM
1st timeslip from new combo, please comment Camaro76350 Performance 5 Nov 16th, 03 12:52 PM

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