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Expert Carburetor Advice needed

Old 04-07-2013, 10:30 PM
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Default Expert Carburetor Advice needed

ok, so for those of you that have been following my build in the convsersion section, i need some help now. before i bolted the carb on i made sure the t slots were just a little square that was exposed. got the truck running and it idles fine but i only have the idle screws maybe 1/4 turn out each. it is a holley 650dp with mehanical secondaries and 4 corner idle. im pulling about 21" of vaccum at idle at 900 rpm. when the idle screws get turned out to 1.5 turns where i was told they should be its so rich i can barely see. am i correct in assuming that i need a larger idle air bleed?
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Old 04-07-2013, 10:50 PM
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I have not seen your thread. Depends on the engine size. A turn and a half works for me on a 2 corner idle circuit. On a 4 corner, it is much less for me. Usually 1/2-3/4 turn out. So you seem to be in the ball park to me.
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Old 04-07-2013, 10:54 PM
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2000 s10 with a 4.8, 4l80 full manual valvbody and a ford 8.8" with 4.10s. as soon as i get the spacers in the mail itll get a procharger soon once i get the carb dialed in
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Old 04-07-2013, 11:25 PM
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Just keep tuning, it takes time and once you start boosting it, you will tune some more.
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Old 04-07-2013, 11:31 PM
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When I changed my air bleeds it more changed the rpm at where the carb changed from its idle circuit to the main jets(?) I went one extreme to the other an took test drives last year and I just remember watching the wideband go one extreme to another at different rpms the larger I made my bleeds. So now I'm attempting to change the ifr size to help set my idle afr. Right now I'm at 3/4 turns out on all 4 corners and I'm too rich at idle, if I lean out any more the engine goes dead lean under a load. I'm thinking makin the restrictors smaller will allow me to get my screws out that 1-1/2 turns out and still be lean at idle and have good flow under load. I'm hoping this is correct lol ice spent all winter working on hand made jets and research lol.
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Old 04-08-2013, 06:11 AM
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LS motors do that with out of the box Holley's for some reason. Mine are about a half turn. Most guys are similar. If you want to regain some control you need to adjust the idle feed restrictors and maybe idle air bleeds. I haven't bothered changing mine cause it is otherwise running perfectly.

With most Holley's adjusting the IFR's and air bleeds means drilling out the press in restrictions then tapping them for set screws that you drill yourself to whatever size is needed.

Last edited by Pop N Wood; 04-09-2013 at 06:25 AM.
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Old 04-08-2013, 06:08 PM
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I was having similar issues with my 850 demon. ended up about 5/8 of a turn. anything else was too rich.
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Old 04-08-2013, 08:44 PM
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ill be ordering some 6/32 8/32 and 10/32 brass set screws and precision drill bit set next pay check so i can make my own bleed and jets and start playing with the carb some
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Old 04-08-2013, 11:42 PM
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1.5 Turns is ONLY a Starting point! Don't really worry about how many turns out Untill it takes almost 2 full turns. A 650 Is way to small and will run rich do to the low air Volume.
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Old 04-09-2013, 07:13 AM
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Too small for a bone stock 4.8? I dont think so but thats me...
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Old 04-09-2013, 11:31 AM
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Acording to the carb calculator 650 is ideal for 7000 rpms on a 4.8. Is this a demon, or holley carb?
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Old 04-09-2013, 11:51 AM
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Originally Posted by ZONES89RS View Post
Usually 1/2-3/4 turn out.
Originally Posted by 89gmcs15 View Post
Right now I'm at 3/4 turns out on all 4 corners
Originally Posted by onefast84 View Post
ended up about 5/8 of a turn.
I too range between 5/8 and 3/4 or a turn on all 4 corners.
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Old 04-09-2013, 01:21 PM
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Its a holley 650, pn 82651. I and going to make the IFR smaller so I have more adjustability with the idle screws.thatll have to happen next paycheck though
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Old 04-09-2013, 01:31 PM
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Originally Posted by FakeSnake View Post
Its a holley 650, pn 82651. I and going to make the IFR smaller so I have more adjustability with the idle screws.thatll have to happen next paycheck though
That is not really how it works. Try just closing them further first. I am willing to bet that if you get them around a 1/2 turn each, it should work for you.

When you get into changing IABs and IFRs, plan on spending a lot of time logging with a wideband as each change not only effects idle, but also part throttle cruise.
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Old 04-10-2013, 07:54 AM
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The idle screws are only out 1/4 turn each, turning them out more than that makes it run so rich I cant even stand over the motor to work on it because my eyes are burning so bad... what ive gathered from all the reading ive done is I need to decrease the size of the IFR hole to reduce the amount of fuel available at cruise and idle and possibly increase the size of the idle air bleed slightly. Someone correct me if Im wrong because that is what im thinking.
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Old 04-10-2013, 08:22 AM
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Originally Posted by FakeSnake View Post
The idle screws are only out 1/4 turn each, turning them out more than that makes it run so rich I cant even stand over the motor to work on it because my eyes are burning so bad... what ive gathered from all the reading ive done is I need to decrease the size of the IFR hole to reduce the amount of fuel available at cruise and idle and possibly increase the size of the idle air bleed slightly. Someone correct me if Im wrong because that is what im thinking.
If you close them all the way, will the car still idle? Where is your float level set?
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Old 04-10-2013, 09:35 AM
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What's your timing like?
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Old 04-10-2013, 06:38 PM
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Originally Posted by FakeSnake View Post
The idle screws are only out 1/4 turn each, turning them out more than that makes it run so rich I cant even stand over the motor to work on it because my eyes are burning so bad...
I wouldn't go drilling out IFR's just yet. You might have something else wrong.

Make sure you don't have a bad gasket or gas leak anywhere. Hold the throttles open and look for leaks. Double check the float levels. Clean out any internal passages and the air bleeds. Anything stuck in there will make it run rich as ****. Check for a blown power valve or leaking power valve gasket.

Pull the carb off and measure how much of the transfer slot is showing. You want primary and secondary right around 20 to 30 thousands. Anything less than that then back off your idle timing a bit so you can open the butterflies some. I have found getting the right amount of transfer slot showing on the primary side is the key to getting a smooth transition off of idle.



If all that is good and you still want to experiment with the idle feed restrictors, then bend a very fine piece of wire in kind of a V shape an insert them into both IFR. You need to get them deep, into the press in restriction, not just into the cavity. Using a V shape allows you to trap it against the gasket when you put the metering block on. You can get different diameter wire by pulling them from a stainless steel wire brush.



And don't mess with air bleeds until you get the AFR stable when coming off of idle. You do all of that with the mixture screws and IFR. IFR are for adjusting the AFR right off of idle, air bleeds keep the AFR steady as the RPM increases and the carb moves from the transition circuits to the main circuit.

And like Tigger said keep detailed records of everything you do and how it worked out. If you are like me you will have to rebaseline a a time or three until you get it right. This is especially true before you take a drill bit to anything on the carb.

Last edited by Pop N Wood; 04-10-2013 at 06:52 PM.
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Old 04-11-2013, 12:42 AM
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for ***** and giggles i took it to cecil dragway tonight and ran pretty crappy... 14.95 was the best et but tire spin was really bad... i will check all of the above mention areas and report back for more ideas. timing is pill #6 that came with the msd 6010
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Old 04-21-2013, 05:56 AM
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I ll look at it..
Thanks pop
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