Re: Think my carb is too big
[Re: skep419]
#445921
08/24/09 04:58 PM
08/24/09 04:58 PM
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Joined: Jul 2007
Posts: 531 Virginia
JimG
mopar
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mopar
Joined: Jul 2007
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Quote:
Quote:
13* initial with a xe284 isn't going to cut it. Add at least 5* and limit mechanical to get your total.
My guess, it's loading up because the throttle plates are open too far at idle.
Got more than one 360 with a xe268H running 750dp's with no problems. One gets 20mpg on the highway with 2.76-2.9x gears
Throttle plates are not open to far at idle. Primarys have 1/8" breathers
You've got lots of good advice above, but I'm concerned with your response here. If you know how to check the relationship between the throttle plates and the transition slot at idle, that's fine. If you don't, I'll be more than happy to post a picture that illustrates it.
More than likely, after you follow the advice above and get the timing worked out, you'll be close.
As stated above, the idle and transition circuits can be leaned out if that's what it takes.
Minivan and Rapid Robert:
Regarding the overcarbing discussion, yes the factory put...what?...625 CFM carbs on 440HPs, and those factory engineers were no slouches.
OTOH, I was walking around the pits at Watkins Glen in the late 80's and came across a Firebird with a Buick V6 running a Dominator! The crew chief was in a talkative mood, so I obliged him with questions, the first being "Wassup with a Dommy on 250 cubic inch engine"? He said the Dominator worked out better for them, not because of quantity, but because it provided better quality (presumably better distribution...I don't know). If you followed the formulas, that V6 would have to turn stratospheric RPM - even assuming 100% VE, to work out to 1050 CFM.
Anyway, I never forgot that and think about it ocasionally.
We now return you to the rich 750 DP!
Jim
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Re: Think my carb is too big
[Re: JimG]
#445924
08/25/09 02:49 PM
08/25/09 02:49 PM
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Joined: Apr 2007
Posts: 782 Minnesota
skep419
OP
super stock
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OP
super stock
Joined: Apr 2007
Posts: 782
Minnesota
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Quote:
Quote:
Quote:
13* initial with a xe284 isn't going to cut it. Add at least 5* and limit mechanical to get your total.
My guess, it's loading up because the throttle plates are open too far at idle.
Got more than one 360 with a xe268H running 750dp's with no problems. One gets 20mpg on the highway with 2.76-2.9x gears
Throttle plates are not open to far at idle. Primarys have 1/8" breathers
You've got lots of good advice above, but I'm concerned with your response here. If you know how to check the relationship between the throttle plates and the transition slot at idle, that's fine. If you don't, I'll be more than happy to post a picture that illustrates it.
More than likely, after you follow the advice above and get the timing worked out, you'll be close.
As stated above, the idle and transition circuits can be leaned out if that's what it takes.
Minivan and Rapid Robert:
Regarding the overcarbing discussion, yes the factory put...what?...625 CFM carbs on 440HPs, and those factory engineers were no slouches.
OTOH, I was walking around the pits at Watkins Glen in the late 80's and came across a Firebird with a Buick V6 running a Dominator! The crew chief was in a talkative mood, so I obliged him with questions, the first being "Wassup with a Dommy on 250 cubic inch engine"? He said the Dominator worked out better for them, not because of quantity, but because it provided better quality (presumably better distribution...I don't know). If you followed the formulas, that V6 would have to turn stratospheric RPM - even assuming 100% VE, to work out to 1050 CFM.
Anyway, I never forgot that and think about it ocasionally.
We now return you to the rich 750 DP!
Jim
Both primary and secondary trans slots look like little squares (not rectangles). The primary plates have been drilled 1/8"
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Re: Think my carb is too big
[Re: skep419]
#445925
08/25/09 02:53 PM
08/25/09 02:53 PM
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Joined: Jul 2007
Posts: 531 Virginia
JimG
mopar
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mopar
Joined: Jul 2007
Posts: 531
Virginia
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Quote:
Both primary and secondary trans slots look like little squares (not rectangles). The primary plates have been drilled 1/8"
OK, now I understand, and that sounds right. Carry on!
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Re: Think my carb is too big
[Re: Supercuda]
#445928
08/26/09 01:36 PM
08/26/09 01:36 PM
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Joined: Apr 2007
Posts: 782 Minnesota
skep419
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Quote:
You have to tune the idle circuit and I am not talking about the idle mixture screws here. There are innumerable books out there on how to tune a Holley, get one, read it, ask us questions till you understand it then buy a wideband O2 sensor and tune the Holley.
Ordered How to Super Tune a Holley should be here friday. Should be a master buy Monday.
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Re: Think my carb is too big
[Re: JimG]
#445930
08/27/09 02:03 PM
08/27/09 02:03 PM
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Joined: Apr 2007
Posts: 782 Minnesota
skep419
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Quote:
Skep419, where are you at this point?
1 turn out on the idle mixture screws, and (I'm assuming) still a stinky idle? And since you only have 1 turn on the idle mixture screws, I'm assuming (again) that they're quite sensitive?
You might go beyond 16* initial timing just to see if the engine likes it. Don't hammer on it b/c you'll have too much timing at higher RPM, just putt around the block and see if it helps.
If the idle is still rich after that, it's time for larger Idle Air Bleeds and/or smaller Idle Feed Restrictions, as previous posters said. Long term, both of these mods require drilling and tapping on your carb. Short term, you can install a properly-sized wire in the IFR to partially block it. Shout back if you're interested, as there are plenty of people here who can walk you thought it.
Jim
At this point I am waiting for the book. Still stinky idle. Anything over one turn on the idle mixture and it loads up. I have a 600 dp holley and a 750 vac sec ede that I am going to try out until I have read the holley book a couple times.
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Re: Think my carb is too big
[Re: skep419]
#445931
08/29/09 02:52 PM
08/29/09 02:52 PM
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Joined: Apr 2007
Posts: 782 Minnesota
skep419
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Ok so I read the book. I dont think I want to mess with the air bleeds (drilling anyway). They talk about the wire trick and that sounds like it would be worth a try. I got the vacuum up to 11 at idle now by adj the sec transfer slot a tad. It no longer loads up in gear at stop signs. zero hesitation. still stinks a little but I think I can live with it. Idle mixture screws still get the best vacuum with 1 turn out. There is still a popping coming out of the exhaust at cruise speeds less then 2500 rpm. I will have to read up on the main circuit tricks. (maybe a little fat on the primary side or power valve still to big) I need to get a longer vacuum hose so I can cruise with the gauge in the car
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Re: Think my carb is too big
[Re: skep419]
#445932
08/29/09 05:13 PM
08/29/09 05:13 PM
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Joined: Jul 2007
Posts: 531 Virginia
JimG
mopar
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mopar
Joined: Jul 2007
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Quote:
still stinks a little but I think I can live with it.
We're Mopar guys, mon! We settle for nothing less than perfection!
Seriously, the wire trick is great because it allows folks to modify their carb without getting that queasy feeling that comes along with taking a drill to it. You probably already figured this out, but the downside is, once you've done all your pi R squared math and figured out the wire size to reduce the passage by 6%, you put the wire in just a few degrees off from parallel and all you math goes out the window, as the wire now has a larger footprint. It must, must, must be quare in the hole. I've seen people give up and just "live" with a badly tuned carb because the wire trick didn't work for them.
The better solution (if you have the stomach for it ) is to drill and tap the idle feed restriction (after carefully measuring it) to 6-32 and drilling a 6-32 X 1/8 set screw to the desired size and screwing it in. See pic.
The advantage is you bypass the kludginess of using wire.
All you doing is drilling out a pressed-in brass orfice, and slightly enlarging the hole beyond it, which is soft and easily drilled.
Anyway, it's something to consider. It's not a big deal, but I can certainly understand an unwillingness to attack a perfectly good carb with a drill!
Jim
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Re: Think my carb is too big
[Re: JimG]
#445935
09/01/09 07:36 PM
09/01/09 07:36 PM
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Joined: Apr 2005
Posts: 12,271 Overpriced Housing Central
RobX4406
I Live Here
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I Live Here
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Posts: 12,271
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Quote:
You might go beyond 16* initial timing just to see if the engine likes it. Don't hammer on it b/c you'll have too much timing at higher RPM, just putt around the block and see if it helps.
Jim
Good advice there.
Is it into the mechanical advance in neutral and then backing that advance out in gear because of the RPM drop? Happens all the time.
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Re: Think my carb is too big
[Re: skep419]
#445936
09/01/09 09:57 PM
09/01/09 09:57 PM
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Joined: Jul 2007
Posts: 531 Virginia
JimG
mopar
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mopar
Joined: Jul 2007
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Quote:
The wire is in and it helped a little but now it pops out of the carb when I roll into the throttle. Doesnt skip a beet when I mash it. still likes the mixture screws no more than 1 turn out. Idles in gear between 3-5 vacuum, out of gear at 11 and cruise speeds at 15.
If I give it a accell pump shot while idling out of gear it bogs and dies. So it must still be way rich.
Something is fishy about that!
What size is your existing IFR and what size wire did you put in it?
Since you got a Holley book and read it recently you probably already know this, but just in case you somehow missed it: IFRs can be located in two different places in Holley metering blocks. The one I posted a pic of is the location where you'd find it in older Holley carbs. Some newer ones (and most clones) have the IFR mounted higher and farther outboard. Is it possible you choked the wrong passage? Just a thought.
If you block the IFR with wire that effectively reduces the IFR by, say, 10% you should see positive results on the mixture screws, assuming the problem is IFRs that are too big.
If you can tell me what size IFR you've got now, I can probably get you in the ballpark. I'd need to know the size of the Idle Air Bleed, too. That's probably what we should have done before you tried the wire. Hindsight, 20/20, etc.
Jim
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Re: Think my carb is too big
[Re: skep419]
#445938
09/02/09 07:13 AM
09/02/09 07:13 AM
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Joined: Jul 2007
Posts: 531 Virginia
JimG
mopar
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mopar
Joined: Jul 2007
Posts: 531
Virginia
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OK, I didn't realize you had a Street HP series. For some reason, I was thinking it was a "classic" double pumper with press-in air bleeds, etc.
I've never worked on one of these carbs, but I've worked on a bunch of "regular" HP Holleys, and every one of them had the high-mounted IFR. Keep in mind that there will be an orfice in the location illustrated in the pic I posted, it just won't have an brass restrictor pressed into it.
The pic I posted was to illustrate the techniqe of converting the metering block to screw-in IFRs, and not necessarily to say "put wire here". Sorry if it confused you.
Look back through your book and find all the illustrations of metering blocks you can find. See if you can find one that shows the alternate location for IFRs. Then, using numbered drill bits (the shank end) find out which orfice has the restrictor pressed into it, and what size it is. If it's larger than .040", you're probably barking up the wrong tree.
I don't have a block laying around right now that has the IFR in the alternate location. If I did, I'd post a pic for you. Perhaps someone else would post one. Hint, hint!
Jim
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