Holley 4150 on stock 302

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MNBelv57

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Aug 20, 2011
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Location
New York
My Car
72' Mustang
Hello all, haven't posted in a while so I hope everyone is well and enjoying their cars. I hope someone can help with a frustrating problem I am having. I have a 72' convertible with stock 302 except for headers, dual exhaust Petronix conversion kit with Petronix coil and 8mm spark plug wires. I had the stock intake with two barrel until recently when I changed to a Summit Stage 1 intake which is described as a stock replacement for a four barrel car, and a Holley 4150 600cfm carb. I had the carb. since the 80's and got it used from a friend who said it was off a Chevy 350. I had this carb. on a Weiand Action Plus high rise intake some years ago and when some friends tuned it the car ran really well with great throttle response and plenty of power for a stock motor. For some reason it started running poorly and out of frustration I put the old 2bbl. back. Like I said this was quite a few years ago. So, I thought I would try the 4bbl. again. I rebuilt it and put it on the car but it doesn't idle smoothly and you can really smell the unburnt gas. The plugs were getting badly fouled too. I adjusted the floats as per Holley's instructions with the fuel level at the bottom of the sight plug and also adjusted the air fuel mixture screws with a vacuum guage to get the highest amount of vacuum. I also adjusted the timing to 6 degree BTDC as per the cowl sticker tune up instructions and set the idle to 575 RPM's in drive (for auto. trans. cars). But it is still running lousy and sounds really anemic. Since I don't know the origin of this carb., I figured that the jets might be too large so I took off the primary bowl and found that both jets were #66, the power valve was #65 and the squirter nozzle was a #25. I called the Summit Racing Tech. line and gave all these specifications to the technician but he thought that the combo was about right for a stock car. I am a little stumped here and by no means am I very experienced at this but I really want to get this car running strong again so I can enjoy it. Any help is greatly appreciated. Thanks, Mario

 
You might try bumping the base timing up to 10-12*. Also a carb tear down and cleaning would probably go a long way.
+1 increase initial timing. You are probably idling on the t slot which accounts for the richness (is that a word?)

What is the List number of the carb? It should be on the choke horn.

 
You might try bumping the base timing up to 10-12*. Also a carb tear down and cleaning would probably go a long way.
+1 increase initial timing. You are probably idling on the t slot which accounts for the richness (is that a word?)

What is the List number of the carb? It should be on the choke horn.

Tommy, the list # is 1850-2 1196.

 
You might try bumping the base timing up to 10-12*. Also a carb tear down and cleaning would probably go a long way.
Thanks Mike. Actually I did rebuild it about a year ago and this fall is the first time I took it out since then.

 
You might try bumping the base timing up to 10-12*. Also a carb tear down and cleaning would probably go a long way.
+1 increase initial timing. You are probably idling on the t slot which accounts for the richness (is that a word?)

What is the List number of the carb? It should be on the choke horn.

Tommy, the list # is 1850-2 1196.
OK I think that should be a 4160 VS carb with a single metering block on the primary side. Is that the case? If so it should work fine for you.

Try increasing the timing. That will raise the idle speed which will allow you to close the front butterfly and get you off the transition slot.

 
A blown power valve would produce these symptoms (a 6.5 in/hg PV is not appropriate for a stock cam 302). Too much of the transfer slot being uncovered or too large of an idle channel restrictor would also produce these symptoms. Holley 1850s are a "universal" replacement carbs. That means the calibration is universally wrong. Almost all carbs will require some calibration to get close to optimal performance as each engine has different specifications and parts. Chuck

 
+1 increase initial timing. You are probably idling on the t slot which accounts for the richness (is that a word?)

What is the List number of the carb? It should be on the choke horn.

Tommy, the list # is 1850-2 1196.
OK I think that should be a 4160 VS carb with a single metering block on the primary side. Is that the case? If so it should work fine for you.

Yeah Tommy it does have the single metering block on the primary side. I am waiting on some gaskets but will try the timing like you said. Thanks again.

Try increasing the timing. That will raise the idle speed which will allow you to close the front butterfly and get you off the transition slot.

 
A blown power valve would produce these symptoms (a 6.5 in/hg PV is not appropriate for a stock cam 302). Too much of the transfer slot being uncovered or too large of an idle channel restrictor would also produce these symptoms. Holley 1850s are a "universal" replacement carbs. That means the calibration is universally wrong. Almost all carbs will require some calibration to get close to optimal performance as each engine has different specifications and parts. Chuck
Chuck, if increasing the idle doesn't work, what size power valve do you think would work and do the jet and squirter nozzle have to be changed too. Also, how do you check if your power valve is blown. Thanks, Mario.

 
You need to apply vacuum to the flat side of the PV to see if it closes and stays closed. I'd guess a stock came 302 would generate at least 15 in. of vacuum so probably a 10.5 PV would work. How much vacuum are you seeing? Do the mixture screws have a significant affect on idle speed? How many turns out yields best idle quality? Don't worry about the shooter size until you get the idle circuit working properly. If you turn the carb upside down, how much of the transfer slot is exposed (more than about .035 is too much). Set the idle screw so that about .025 is exposed, reinstall and don't adjust the idle screw. If the mixture screws won't adjust the idle speed to an acceptable speed and quality, the idle channel restrictor is too large. You can insert a thin wire (about .015-.020) in the restrictor to see if you have better idle quality control with the mixture screws. An alternative is to drill a hole (.080-.100) in the primary throttle blades towards the front of the blades. This acts as an idle air bypass and leans the mixture. You can also try opening the secondary idle screw about 1/16-1/8 of a turn to see if that allows you to close the idle screw to cover more of the primary transfer slots. I suggest you google "holley idle channel restrictor" or "holley idle circuit" to get visual representations of what I'm trying to explain. Getting any carb properly calibrated is not an easy thing to do, most of the time. Chuck

 
You need to apply vacuum to the flat side of the PV to see if it closes and stays closed. I'd guess a stock came 302 would generate at least 15 in. of vacuum so probably a 10.5 PV would work. How much vacuum are you seeing? Do the mixture screws have a significant affect on idle speed? How many turns out yields best idle quality? Don't worry about the shooter size until you get the idle circuit working properly. If you turn the carb upside down, how much of the transfer slot is exposed (more than about .035 is too much). Set the idle screw so that about .025 is exposed, reinstall and don't adjust the idle screw. If the mixture screws won't adjust the idle speed to an acceptable speed and quality, the idle channel restrictor is too large. You can insert a thin wire (about .015-.020) in the restrictor to see if you have better idle quality control with the mixture screws. An alternative is to drill a hole (.080-.100) in the primary throttle blades towards the front of the blades. This acts as an idle air bypass and leans the mixture. You can also try opening the secondary idle screw about 1/16-1/8 of a turn to see if that allows you to close the idle screw to cover more of the primary transfer slots. I suggest you google "holley idle channel restrictor" or "holley idle circuit" to get visual representations of what I'm trying to explain. Getting any carb properly calibrated is not an easy thing to do, most of the time. Chuck
Chuck, my vacuum in drive is about 15 but the needle jumps about every 2 seconds. In park I get about 19 on the vacuum with a steady reading. The mixture screws don't seem to have too drastic an effect when turned all the way in but I got the best vacuum reading with both sides turned out about one and a half turns. Thanks, Mario.

 
You need to apply vacuum to the flat side of the PV to see if it closes and stays closed. I'd guess a stock came 302 would generate at least 15 in. of vacuum so probably a 10.5 PV would work. How much vacuum are you seeing? Do the mixture screws have a significant affect on idle speed? How many turns out yields best idle quality? Don't worry about the shooter size until you get the idle circuit working properly. If you turn the carb upside down, how much of the transfer slot is exposed (more than about .035 is too much). Set the idle screw so that about .025 is exposed, reinstall and don't adjust the idle screw. If the mixture screws won't adjust the idle speed to an acceptable speed and quality, the idle channel restrictor is too large. You can insert a thin wire (about .015-.020) in the restrictor to see if you have better idle quality control with the mixture screws. An alternative is to drill a hole (.080-.100) in the primary throttle blades towards the front of the blades. This acts as an idle air bypass and leans the mixture. You can also try opening the secondary idle screw about 1/16-1/8 of a turn to see if that allows you to close the idle screw to cover more of the primary transfer slots. I suggest you google "holley idle channel restrictor" or "holley idle circuit" to get visual representations of what I'm trying to explain. Getting any carb properly calibrated is not an easy thing to do, most of the time. Chuck
Chuck, my vacuum in drive is about 15 but the needle jumps about every 2 seconds. In park I get about 19 on the vacuum with a steady reading. The mixture screws don't seem to have too drastic an effect when turned all the way in but I got the best vacuum reading with both sides turned out about one and a half turns. Thanks, Mario.
If it still runs with the mixture screws all the way in it is because too much of the transfer slot is uncovered, or an internal leak of some kind. It sure sounds like the idle channel restrictor is too large. As others have said, advancing the timing a bit my help some. Chuck

 
I agree with Chuck, probably too much of the idle transfer slot is exposed because you have the idle screw turned in too far to compensate for the rough idle. Have you checked your plugs and points for correct gap/dwell. You'll also need to pull your spark plugs and clean them until you get it running correctly. Verify you have the correct plugs and they're not too cold of a heat range.

Advancing the timing will speed up your idle and may allow you to back off the idle screw enough to cover the transfer slot, and adjust the idle mixture.

With the carburetor on a stand on your workbench I would fill the bowls and see if you have any obvious internal leakage, from either damage or a porous casting.

 
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