Author Topic: slight hesitation  (Read 4243 times)

william1

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slight hesitation
« on: December 07, 2009, 04:07:51 PM »
 after installing a new holley 4br 4479, i picked up a slight hesitation in throttle response it's always from a dead stop at 1st gear, i have a new fuel pump, new tank which i did not install but it looks fine when i had it out, also new fuel cap, changed fuel filter, new fuel line, the manifold is the old tarantula by holley, i'm thinking that the standard out of the box pump just isn't enough pressure or gpm to keep it happy,,,, any suggestions.

BlackoutSteve

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Re: slight hesitation
« Reply #1 on: December 07, 2009, 06:21:24 PM »
With your floats at the correct level, you should be able to turn off your fuel pmp and have no hesitation with a properly adjusted carb.
...in other words, your fuel pump is far from the cause here.

Make sure your accelerator pump lever is adjusted so it moves the lever with the slightest throttle movement, and doesn't bottom out/bind the accel pump at full throttle.
The cause of the hesitation will most likely be that the shooter/s are too small. Step up one size on the primary and see what happens. That should make an improvement..
Restoring my RHD 69 Jane in Melbourne, Australia.
http://www.usmuscle.com.au/Forum/showthread.php?t=2840

Stingr69

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Re: slight hesitation
« Reply #2 on: December 07, 2009, 08:50:32 PM »
Pump adjustment is the first thing that comes to mind.
I am with Steve.

You must not have ANY slack in the accelerator pump linkage AND have about .015" ADDITIONAL travel available on the pump arm with the throttle open all the way so you do not bottom out the accelerator pump when you floor it to WOT.

What color accelerator pump cam are you running?

-Mark.

hotrod68

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Re: slight hesitation
« Reply #3 on: December 08, 2009, 05:37:23 AM »
I'm confused about the manifold--the Tarantula was the old TM-1 made by Edelbrock, not Holley. If it's a TM-1 then it's a single-plane, and maybe as was suggested, you need a bigger squirter or a different pump cam--a single-plane manifold requires more intial pump shot than a dual-plane. The existing pump cam can also be adjusted by removing the screw and rotating the cam on the shaft. When you move the throttle lever the pump should instantly begin to shoot gas from the squirter in 2 hard streams--that's the first thing I'd check. I'd also make sure there are no unplugged vacuum taps that are leaning the engine out at idle. My 2 cents and good luck!

HotRod'68  1968 SS350 coupe undergoing frame-off resto/rod. 386/350/4.11s
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Sauron327

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Re: slight hesitation
« Reply #4 on: December 08, 2009, 03:01:16 PM »
While you're under the hood read John Z's timing article and check your timing and VA can. Listening to his advice improved my performance tremendously; along with changes to my carb.

william1

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Re: slight hesitation
« Reply #5 on: December 08, 2009, 03:56:06 PM »
 guys thanks for the hints,,, am going through the clutch, flywheel and muncie,  right know as soon as i get this thing back on the ground i'll dive into it,, your right not a holley,, had holley on the brain that morning, great info great suggestions.

  oh,,, shoot me a link to timing article, again thanks...

rich69rs

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Re: slight hesitation
« Reply #6 on: December 08, 2009, 05:10:01 PM »
http://www.camaros.org/forum/index.php?topic=5534.0

Read the above link in its entirety.  Copy and paste John's Timing 101 article into a Word document and save it somewhere for future reference.

Good luck

Richard
Richard Thomas
1969 RS

william1

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Re: slight hesitation
« Reply #7 on: December 10, 2009, 02:09:57 PM »
back to the post,, finished up my latest project, clutch, flywheel, muncie, just in time for the snow, but did manage to give it a quick spin, now to the hesitation, i have instant fuel from the discharge nozzles, and no vacuum leaks that that i can detect, 31 is on the nozzle, so i assume that's .031, it was mentioned to go bigger,,, so if i was to try this, how many and what range were you thinking.

just a side note, i have to tell you guys that i know just enough to get my self in trouble, but since i started this journey with my 69z,, well im having riot, this is some fun stuff, with results that you can see and feel.

BlackoutSteve

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Re: slight hesitation
« Reply #8 on: December 11, 2009, 09:45:06 AM »
Next size up is a 35.. Try that.  ;)
Restoring my RHD 69 Jane in Melbourne, Australia.
http://www.usmuscle.com.au/Forum/showthread.php?t=2840

JohnZ

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Re: slight hesitation
« Reply #9 on: December 11, 2009, 04:27:51 PM »
Double-pumpers are notoriously difficult to tune for normal street operation/driveabililty, which is why they weren't used in production; keep working with the accelerator pump, cam, and squirters and eventually you'll find an acceptable compromise. It's a lot easier to tune a vacuum-secondary Holley.
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william

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Re: slight hesitation
« Reply #10 on: December 11, 2009, 08:39:35 PM »
If you are using an original ducted hood air cleaner with a 90 vent tube it can contact the rear pump lever causing a constant fuel stream. Later air cleaners had a vent tube with 2 45 bends to clear the lever. Or use several air cleaner gaskets...

melav8r

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Re: slight hesitation
« Reply #11 on: December 22, 2009, 05:33:36 PM »
You need one of these to help u tune that Holley. Invaluable toolbox reference:

http://cgi.ebay.com/Holley-4150-4160-Carburetor-Handbook-Mike-Urich-Paperback-1980_W0QQitemZ341307237285QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item4f777f23a5

You can also call Holley tech service and they can make suggestions for squirters, cam, jets, and powervalve based on your particulars. First check your vacuum at idle before calling:
  http://www.holley.com/TechService/
  http://www.holley.com/TechService/Library.asp

btw, did you mean a 4779?
« Last Edit: December 22, 2009, 05:51:13 PM by melav8r »

L78 steve

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Re: slight hesitation
« Reply #12 on: February 17, 2010, 05:51:55 PM »
Was this issue ever resolved?
69 Z/28 Dover White X33,ZL2,PS,M20,Std.int.04C
67 SS/RS Mt. Green 1W,2LGSR,3SL,4K,5BY,07C
70 Nova L78 Blk. Cherry,Sandalwood,M21,02B

william1

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Re: slight hesitation
« Reply #13 on: February 18, 2010, 01:53:15 PM »
as my kid says,,, my bad,,  yes one size larger shooter did the trick, i would have to go and look again to remember which size i removed and which size i installed, just another example, in the way this site and it's members can help.

L78 steve

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Re: slight hesitation
« Reply #14 on: February 18, 2010, 06:20:05 PM »
Great you resolved the problem. I had a similar "dead spot"  I'll call it and I increased the primary jets from 68 to70's and this also worked.
69 Z/28 Dover White X33,ZL2,PS,M20,Std.int.04C
67 SS/RS Mt. Green 1W,2LGSR,3SL,4K,5BY,07C
70 Nova L78 Blk. Cherry,Sandalwood,M21,02B