Holley 950 HP Q..
Thread Starter
Melting Slicks
Joined: Feb 2002
Posts: 2,298
Likes: 1
From: Sodertalje/Sweden
Holley 950 HP Q..
I noticed the other day when changing the intakegasket that my Pri throttleplates were closed and the Sec plates was slightly open.
This doesnt sound right,does it?
This should mean that the idle is going through the Sec venturis?
Does any one know how to properly change this so i can adjust the carb acording to Lars Techpaper?
This doesnt sound right,does it?
This should mean that the idle is going through the Sec venturis?
Does any one know how to properly change this so i can adjust the carb acording to Lars Techpaper?
Tech Contributor
Joined: Aug 1999
Posts: 14,377
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From: At my Bar drinking and wrenching in Lafayette Colorado
BB -
The primary and secondary throttles should be cracked open the same amount for a proper setup. If your primaries are fully closed and your secondaries are cracked open, you need to close the secondaries slightly and crack the primaries a little more. Use the secondary idle speed screw to slightly close them. But both throttle shafts should be cracked (equally) to produce best idle. Do you have a copy of my BG Tuning Paper? This describes best how to balance the shafts out. Drop me an e-mail if you need it.
V8FastCars@msn.com
The primary and secondary throttles should be cracked open the same amount for a proper setup. If your primaries are fully closed and your secondaries are cracked open, you need to close the secondaries slightly and crack the primaries a little more. Use the secondary idle speed screw to slightly close them. But both throttle shafts should be cracked (equally) to produce best idle. Do you have a copy of my BG Tuning Paper? This describes best how to balance the shafts out. Drop me an e-mail if you need it.
V8FastCars@msn.com
Safety Car
Joined: Jul 2002
Posts: 3,770
Likes: 3
From: St Louis MO
The secondary idle screw is on the bottom of the pass side of the carb, really hard to get to with the carb on the manifold. Holley makes a $30 kit that moves the screw to the top of the secondary throttle shaft, allowing idle changes just like the primary side.
Brett
Brett
Thread Starter
Melting Slicks
Joined: Feb 2002
Posts: 2,298
Likes: 1
From: Sodertalje/Sweden
Since i got really bored today i looked up my List# (80496) on the carb and checked what kind off jets it came with from Holley. Mortec said 75/75 and i`ve got 84/86 on it now.
The problem i`m chasing is that it fouls plugs really bad,really quick and is kinda sluggish off idle.All this points in the direction of way to big jets.
Should i rejet the carb and give a try?
The problem i`m chasing is that it fouls plugs really bad,really quick and is kinda sluggish off idle.All this points in the direction of way to big jets.
Should i rejet the carb and give a try?
Melting Slicks
Joined: Apr 2000
Posts: 3,286
Likes: 8
From: San Jose California
BB Wowbagger,
I've got the same carb on my L88. I spent the best part of this weekend getting it dialed in. My carb also came with 78's all 'round. Yes, the secdondaries should be cracked open just a little.
Using a Innovative dgital A/F sensor, I found that the 4 idle screw absolutely effect the a/f even at highway cruising speeds. Go back to original jetting and carefully tune the 4 idle screws with a vacuum gauge. All the screws should be within 1/4 turn of each other when done. Be very careful not to torque down on the screws when turning in. The tip at the end of the screw is easily damaged by anything more than a gentle touch once the screw is turned all the way in. You will probably find that somewhere between 3/4 and 1.5 turns is about right. Even a 1/16th of a turn changed the a/f about half a number (i.e. 14 vs. 14.5:1) at idle and cruise. BUT, the amount that the primary and secondary throttle plates are each cracked will effect this big time.
I ended up changing the screw in air bleeds too to get it perfect. The air bleed kits are very expensive, but I was able to get the carb dialed in perfectly with my engine. Should be around 20mpg at 70mph, not too bad for 500 horse power at the real wheels.
Chuck
I've got the same carb on my L88. I spent the best part of this weekend getting it dialed in. My carb also came with 78's all 'round. Yes, the secdondaries should be cracked open just a little.
Using a Innovative dgital A/F sensor, I found that the 4 idle screw absolutely effect the a/f even at highway cruising speeds. Go back to original jetting and carefully tune the 4 idle screws with a vacuum gauge. All the screws should be within 1/4 turn of each other when done. Be very careful not to torque down on the screws when turning in. The tip at the end of the screw is easily damaged by anything more than a gentle touch once the screw is turned all the way in. You will probably find that somewhere between 3/4 and 1.5 turns is about right. Even a 1/16th of a turn changed the a/f about half a number (i.e. 14 vs. 14.5:1) at idle and cruise. BUT, the amount that the primary and secondary throttle plates are each cracked will effect this big time.
I ended up changing the screw in air bleeds too to get it perfect. The air bleed kits are very expensive, but I was able to get the carb dialed in perfectly with my engine. Should be around 20mpg at 70mph, not too bad for 500 horse power at the real wheels.
Chuck
Last edited by Chuck Harmon; Sep 7, 2004 at 02:53 AM.
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Thread Starter
Melting Slicks
Joined: Feb 2002
Posts: 2,298
Likes: 1
From: Sodertalje/Sweden
Yop,you guys are right.I wrote #75`s instead of #78`s. Could the big jets make the idletuning a bit harder? It shouldnt,right?
Man, those EFI setups looks nicer and nicer
Man, those EFI setups looks nicer and nicer
Safety Car
Joined: Jul 2002
Posts: 3,770
Likes: 3
From: St Louis MO
Carb tuning
It aint that hard. It's really easy with an O2 sensor. It can be done by reading plugs but that's kinda iffy. If you have a track nearby you can tune by 1/4 mile mph. I ended up with jets 2 sizes lower than stock (down to 78s from 80s) and 2 small wires in the idle circuits.
Brett
Brett
Thread Starter
Melting Slicks
Joined: Feb 2002
Posts: 2,298
Likes: 1
From: Sodertalje/Sweden
Today i bought new jets and some new nonstick gaskets. I got #78s allround and installed my old 6.5 PVs.
Just for the fun of it i took it for a spin with my old dirty sparkplugs and there seem to be some power loss and a small stumble if i`m rolling at 1400rpm in second and stomp it..
I removed the sparkplugs and saw that they were starting to get a bit lighter in color. Next test will be with new sparkplugs.
Still trying to figure out how to tune the idlescrews properly.
But the engine feels a bit more crisp in throttle respons.
Just for the fun of it i took it for a spin with my old dirty sparkplugs and there seem to be some power loss and a small stumble if i`m rolling at 1400rpm in second and stomp it..
I removed the sparkplugs and saw that they were starting to get a bit lighter in color. Next test will be with new sparkplugs.
Still trying to figure out how to tune the idlescrews properly.
But the engine feels a bit more crisp in throttle respons.
Safety Car
Joined: Jul 2002
Posts: 3,770
Likes: 3
From: St Louis MO
Usually, adjusting the idle screws for max vacuum at idle is good. However, remember they only affect the VOLUME of the idle mixture, NOT the ratio....so sometimes a lean stumble can be fixed by backing out the idle screws 1/8 of a turn or so....but, usually you will need to go up another size in jetting (try some 80s and see what happens...i've got 4 80s if you need them). Remember that the accelerator pump also plays a role in engine bahavior when you press the go-pedal.
Brett
Brett
Melting Slicks
Joined: Apr 2000
Posts: 3,286
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From: San Jose California
I know that many Holley books state that the idle screws don't effect a/f, but this is not the case with my 950hp. The idle screws absolutely effect the a/f at both idle and highway cruise. My digital sensor shows a very wide range, from at least ~17:1 to ~12:1 using only the idle screws.
Chuck
Chuck
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Joined: Jul 2002
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From: St Louis MO
Originally Posted by Chuck Harmon
I know that many Holley books state that the idle screws don't effect a/f, but this is not the case with my 950hp. The idle screws absolutely effect the a/f at both idle and highway cruise. My digital sensor shows a very wide range, from at least ~17:1 to ~12:1 using only the idle screws.
Chuck
Chuck
Brett
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Joined: Jul 2002
Posts: 3,770
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From: St Louis MO
Originally Posted by BB wowbagger
I now run the idle screws at 1 1/2 turn out due to the fact that i know this will work. I tried to fibble with them but i really feel that this is out of my league 
Brett
