Holley Question
Thread Starter
Le Mans Master
Joined: Oct 2001
Posts: 5,943
Likes: 3
From: Wildwood IL
Holley Question
Say...I have a Holley 4160 (750cfm vac secondaries) on my 406 and at idel it's running very rich. I've played with the idel mix screws and at 1 turn out the exhaust is still burning my eyes, along with soot coated spark plugs. Also tried to set idel mix with a vac gage with same results. Do the primary jets effect the idel mix???? Have to check...but I think the primaries are either 74 or 76.
thanks guys
Eddie
thanks guys
Eddie
Drifting
Joined: May 2005
Posts: 1,601
Likes: 0
From: BETHEL PARK PENNSYLVANIA
jets dont affect the idle quality. put a vac gauge and get a reading, and check your power valve in the front of the carb. it may be blown or you need 1 that is 2" less than your vac reading at idle. make sure your timing is set first.
vc
vc
Le Mans Master
Joined: Mar 2004
Posts: 7,458
Likes: 1,484
From: Little Rock AR
Ed,
The jets should not make a difference in the idle mixture. The jets are working at higher airflows.
Verify the float setting is right and the needle and seat are working. Pull the sight plugs out and verify that the gas is just trickling out at idle on a level surface. Adjust as required.
You are probably sucking in gas from the transfer slot. Withouot making any adjustments, pull the carb off and look at the underside of the throttle butterflies. There should be a small portion of the transfer slot exposed. If you have too much exposed, you need to close the throttle blades down untill you have only .020" of the slot length exposed. This slot is about .020" wide so it should look basicaly square when the blades are set right. Start with that and readjust the mixture screws.
That is the easy stuff to try.
-Mark.
The jets should not make a difference in the idle mixture. The jets are working at higher airflows.
Verify the float setting is right and the needle and seat are working. Pull the sight plugs out and verify that the gas is just trickling out at idle on a level surface. Adjust as required.
You are probably sucking in gas from the transfer slot. Withouot making any adjustments, pull the carb off and look at the underside of the throttle butterflies. There should be a small portion of the transfer slot exposed. If you have too much exposed, you need to close the throttle blades down untill you have only .020" of the slot length exposed. This slot is about .020" wide so it should look basicaly square when the blades are set right. Start with that and readjust the mixture screws.
That is the easy stuff to try.
-Mark.
Race Director
Joined: Oct 2000
Posts: 14,997
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From: central FL, near the beach.
Thread Starter
Le Mans Master
Joined: Oct 2001
Posts: 5,943
Likes: 3
From: Wildwood IL
I did try running @ 3/4 turn of the idel mix....she overheated due to lean mix. Also verified float level...but not long enough to notice slow trickel. So...I will try the other below suggestions.
Thank you much for your replies.
Eddie
Thank you much for your replies.
Eddie
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Safety Car
Joined: Oct 2000
Posts: 3,593
Likes: 103
From: Southern Indiana
Get a 4.5 power valve.
set your floats just so the gas is even with the site plug when you take it out while the car is running.
Then with your mixure screws, turn one in slowly until the car runs rough then back it out slowly, watch your turns and count half turns to help, until the idle smooths out, then go to the other side and repeat, do this a couple of times until it smooth.
set your floats just so the gas is even with the site plug when you take it out while the car is running.
Then with your mixure screws, turn one in slowly until the car runs rough then back it out slowly, watch your turns and count half turns to help, until the idle smooths out, then go to the other side and repeat, do this a couple of times until it smooth.
Thread Starter
Le Mans Master
Joined: Oct 2001
Posts: 5,943
Likes: 3
From: Wildwood IL
Tech Contributor
Joined: Aug 1999
Posts: 14,370
Likes: 6,364
From: At my Bar drinking and wrenching in Lafayette Colorado
Say...I have a Holley 4160 (750cfm vac secondaries) on my 406 and at idel it's running very rich. I've played with the idel mix screws and at 1 turn out the exhaust is still burning my eyes, along with soot coated spark plugs. Also tried to set idel mix with a vac gage with same results. Do the primary jets effect the idel mix???? Have to check...but I think the primaries are either 74 or 76.
thanks guys
Eddie
thanks guys
Eddie
Remember to crack that secondary idle speed open as much as the primnary side to equalize airflow through all 4 corners of the carb at idle - it's real important to get the mixture right. Adjust final idle speed using the primary and secondary idle speed screws equally. Typical Holley/BG idle mixture screw setting usually ends up in the 3/4 to 7/8 turn range. Make sure float levels are right at the bottom of the bowl plug.
Burning Brakes
Joined: Sep 2004
Posts: 1,167
Likes: 2
From: Ft.Worth Texas
Rather than start a new thread I would like to add to this one if it is ok.
I have the same holley 750/vac on my 383. It recently developed a fuel leak at the carb after I return from a drive and turn off engine. The fuel appears to drip from around the lower shafts on each side of carb and puddle on the manifold after motor has been off for a few minutes. The holley website says this is caused by percolation and to lower fuel level to 1/8 inch below inspection screw.
What do you guys think? Why would this suddenly appear? Did the alcohol now in the fuel cause this?
btw.. holley says the power valves have blowout protection by means of a check valve and have had for several years.
I have the same holley 750/vac on my 383. It recently developed a fuel leak at the carb after I return from a drive and turn off engine. The fuel appears to drip from around the lower shafts on each side of carb and puddle on the manifold after motor has been off for a few minutes. The holley website says this is caused by percolation and to lower fuel level to 1/8 inch below inspection screw.
What do you guys think? Why would this suddenly appear? Did the alcohol now in the fuel cause this?
btw.. holley says the power valves have blowout protection by means of a check valve and have had for several years.
Last edited by David Ey; Sep 21, 2007 at 09:42 PM.
Tech Contributor
Joined: Aug 1999
Posts: 14,370
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From: At my Bar drinking and wrenching in Lafayette Colorado
Holley is right - I see this all the time. However, lowering the float level may not solve the problem, and it can cause other issues.
The problem occurs (as you guessed from the low boiling point of modern fuels) not from fuel percolating in the float bowl. Rather, the fuel is boiling in the accelerator pump wells. When this happens, the pressure in the well increases, the checkvalve seats, and the expanding fuel will discharge out of the accel discharge nozzles. This fuel drips down onto the throttle blades and is siphoned out of the shafts to drip on the manifold. As soon as the discharge has occurred, the pressure is relieved in the accel pump, it draws more fuel in from the bowl, which starts heating up, and the cycle repeats. This will actually repeat enough times that the majority of the contents of the float bowl will be discharged out of the accel nozzles.
Solution is to install a reflective heat shield under the carb and extending out past the accel pump wells. This will prevent radiant heating from the manifold heating up the fuel in the wells.
The problem occurs (as you guessed from the low boiling point of modern fuels) not from fuel percolating in the float bowl. Rather, the fuel is boiling in the accelerator pump wells. When this happens, the pressure in the well increases, the checkvalve seats, and the expanding fuel will discharge out of the accel discharge nozzles. This fuel drips down onto the throttle blades and is siphoned out of the shafts to drip on the manifold. As soon as the discharge has occurred, the pressure is relieved in the accel pump, it draws more fuel in from the bowl, which starts heating up, and the cycle repeats. This will actually repeat enough times that the majority of the contents of the float bowl will be discharged out of the accel nozzles.
Solution is to install a reflective heat shield under the carb and extending out past the accel pump wells. This will prevent radiant heating from the manifold heating up the fuel in the wells.
Tech Contributor
Joined: Aug 1999
Posts: 14,370
Likes: 6,364
From: At my Bar drinking and wrenching in Lafayette Colorado
If you drop me an e-mail request for my BG Installation paper, I can send you a paper that covers the fabrication of a heat shield:
V8FastCars@msn.com
Lars
V8FastCars@msn.com
Lars
Thread Starter
Le Mans Master
Joined: Oct 2001
Posts: 5,943
Likes: 3
From: Wildwood IL
Eddie -
Remember to crack that secondary idle speed open as much as the primnary side to equalize airflow through all 4 corners of the carb at idle - it's real important to get the mixture right. Adjust final idle speed using the primary and secondary idle speed screws equally. Typical Holley/BG idle mixture screw setting usually ends up in the 3/4 to 7/8 turn range. Make sure float levels are right at the bottom of the bowl plug.
Remember to crack that secondary idle speed open as much as the primnary side to equalize airflow through all 4 corners of the carb at idle - it's real important to get the mixture right. Adjust final idle speed using the primary and secondary idle speed screws equally. Typical Holley/BG idle mixture screw setting usually ends up in the 3/4 to 7/8 turn range. Make sure float levels are right at the bottom of the bowl plug.
Eddie