Need a little Holley help-rich idle circuit
12-08-2012, 09:04 PM
#1
Le Mans Master
Thread Starter
Need a little Holley help-rich idle circuit
I've been trying to get my chassis ready to drop the body on tomorrow and one thing that I have not been able to do is resolve how rich my Holley 3810 is running. The motor is a 327, 10.5:1 SCR, LT1 cam and timing is set 12 degrees initial, 36 degrees all in at 2350 RPM (vacum advance plugged.
The carb is a 3810, every mating surface was initally warped so I used machinist blue and hand filed until I had decent surfaces. Then using progressively finner grades of emory cloth on a sheet of glass, I sanded until I had great mating surfaces all around.
The carb has new Holley needles and seats, 6.5 PV, all new Holley gaskets, 65 pri and 72 secondaries. The floats are set 1/32" below Holley spec and using ethanol free 92 octane. The bowl screws are torqued to 40 inch-pounds per holley instructions.
The transition slot is set to .020" opening and the secondary plates are just barley cracked. The engine fires right up, and idles GREAT, but on the rich side and part of that may be the LT1 cam. The motor runs best with the idle mixture screws no more than 1/2 turn open, runs fine with them closed, when the screws are opened up to 1 or more turns, it becomes really rich and bogs out. Today I tried a different primary metering plate from a spare carb with another new Holley PV but no change.
I started with autolite 3924 plugs but moved up to Autolite 66's a much hotter plug but they are still sooty black.
I thought I would throw this out and see what some other thoughts might be as to why the idle circuit is rich.
TIA
The carb is a 3810, every mating surface was initally warped so I used machinist blue and hand filed until I had decent surfaces. Then using progressively finner grades of emory cloth on a sheet of glass, I sanded until I had great mating surfaces all around.
The carb has new Holley needles and seats, 6.5 PV, all new Holley gaskets, 65 pri and 72 secondaries. The floats are set 1/32" below Holley spec and using ethanol free 92 octane. The bowl screws are torqued to 40 inch-pounds per holley instructions.
The transition slot is set to .020" opening and the secondary plates are just barley cracked. The engine fires right up, and idles GREAT, but on the rich side and part of that may be the LT1 cam. The motor runs best with the idle mixture screws no more than 1/2 turn open, runs fine with them closed, when the screws are opened up to 1 or more turns, it becomes really rich and bogs out. Today I tried a different primary metering plate from a spare carb with another new Holley PV but no change.
I started with autolite 3924 plugs but moved up to Autolite 66's a much hotter plug but they are still sooty black.
I thought I would throw this out and see what some other thoughts might be as to why the idle circuit is rich.
TIA
Last edited by Scott Marzahl; 12-08-2012 at 09:45 PM.
12-08-2012, 10:26 PM
#2
Safety Car
Have you used this carburetor before or is this your first experience with it? If you've used it before, how did it run before?
The first thing to check is the PV, but I'm sure you've checked it already.
The reason I ask about prior usage, is that if there's no assembly problem with it, then it sounds like the idle feed restrictions were drilled larger.
If the IFRs were enlarged, then you can easily restrict them again by inserting fine wire, like those used in a wire brush, in the IFR passages and simply bending the ends over to prevent them from being dislodged.
The LT1 cam has nothing to do with it.
The first thing to check is the PV, but I'm sure you've checked it already.
The reason I ask about prior usage, is that if there's no assembly problem with it, then it sounds like the idle feed restrictions were drilled larger.
If the IFRs were enlarged, then you can easily restrict them again by inserting fine wire, like those used in a wire brush, in the IFR passages and simply bending the ends over to prevent them from being dislodged.
The LT1 cam has nothing to do with it.
Last edited by 65tripleblack; 12-08-2012 at 10:33 PM.
12-08-2012, 10:37 PM
#4
Safety Car
If there is no irregularity in the cleaning and R & R, then the IFR's may have been mucked with, or the secondary plate may have been modified.
Last edited by 65tripleblack; 12-08-2012 at 10:49 PM.
12-09-2012, 08:20 AM
#5
Race Director
sooty plugs is likely poor ignition. need good spark w/10.5
after that is checked and ok,
coat the metering gasket w/grease for a sealing TEST.
check size of IFR, .031"?
if it idles normal for a while, until the grease gets washed off, that proves a bad seal. then careful inspection will show the dry spot as the leak source. IFR junction?
after that is checked and ok,
coat the metering gasket w/grease for a sealing TEST.
check size of IFR, .031"?
if it idles normal for a while, until the grease gets washed off, that proves a bad seal. then careful inspection will show the dry spot as the leak source. IFR junction?
12-09-2012, 03:46 PM
#6
Safety Car
If you're running fine with the idle needles closed, you have more than an idle feed restriction problem, someone drilled out the idle air bleeds, too. If the orifice sizes for the idle feed restrictors and and idle air bleeds are anywhere near the right size, you should idle properly at about 1 1/2 turns opening on the idle mixture screws and should not be fouling plugs with the transition slots open at 0.020 (the recommended setting).
Maybe you'll find some help here:
http://www.carcraft.com/techarticles...e/viewall.html
Maybe you'll find some help here:
http://www.carcraft.com/techarticles...e/viewall.html
12-09-2012, 09:44 PM
#7
If you drill out the idle air bleeds, it will lean out the fuel mixture. Opposite of what happens if you drill out the idle fuel restiction.
Ron B.
Ron B.
12-09-2012, 10:37 PM
#8
Le Mans Master
Thread Starter
Thanks guys, the air bleeds are in the main body but the idle restrictor is in the metering plate correct. Since I swapped out metering plates can't I eliminate the idle restrictor as suspect. I will try to measure the idle bleeds and verify that they are all clear. I do have a spare 3310 main body I can build up with the 3810 fuel bowls and metering plates and see how that compares.
12-10-2012, 03:40 PM
#9
Team Owner
Member Since: Oct 2000
Location: Washington Michigan
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12-10-2012, 06:53 PM
#10
Le Mans Master
12-10-2012, 08:01 PM
#11
Le Mans Master
Thread Starter
John, I hadn't noticed fuel from boosters at idle, only with throttle. Three different PVs with new gaskets. I'm going to check the bleeds if I have time tonight.
