Holley Carb Adjustment
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Mountain Pass
Joined: Sep 2021
Posts: 233
Likes: 36
From: KY
Holley Carb Adjustment
Might need someone to school me on carburetors, first go around messing with one. Rebuilt the 4150 that came with my project. Running very rich. Will run and idle with mixture screws all the way in. Front bowl level is way too high but adjustment doesn’t seem to help.
Any suggestions on where to start? Might be something easy I’m overlooking but everything looked fine the first time I took it off to check the bowl but having the same issues now after putting it back on.
Any suggestions on where to start? Might be something easy I’m overlooking but everything looked fine the first time I took it off to check the bowl but having the same issues now after putting it back on.
Tuned
Joined: Jan 2023
Posts: 305
Likes: 54
From: NC
The mixing screws not functioning could be caused by several things. I'd resolve the bowl float first...make sure it moves freely, inspect the adjustment screw, and make sure the needle and seat are clean. The mix screws not working could mean you have a shot power valve. Did you replace that when you rebuilt the carb? Where are you idling? If the idle screw is cranked in too far, you could be exposing too much of the front transfer slots. This limits the effectiveness of the mixing screws.
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Mountain Pass
Joined: Sep 2021
Posts: 233
Likes: 36
From: KY
Originally Posted by JJFizzle;[url=tel:21605538
21605538[/url]]The mixing screws not functioning could be caused by several things. I'd resolve the bowl float first...make sure it moves freely, inspect the adjustment screw, and make sure the needle and seat are clean. The mix screws not working could mean you have a shot power valve. Did you replace that when you rebuilt the carb? Where are you idling? If the idle screw is cranked in too far, you could be exposing too much of the front transfer slots. This limits the effectiveness of the mixing screws.
Only overfilling the front bowl. Starts right up with no pumps so it must be pouring in from somewhere. I thought maybe it could be fuel pressure from the pump. I have a regulator that I haven’t put on yet but hope to get to this week.
Open to anything else to check while I’m at it. Definitely could just be me being dumb and ignorant my first time through this.
Tuned
Joined: Jan 2023
Posts: 305
Likes: 54
From: NC
Here are a few more ideas:
How do you know you're running rich? With the mixing screws all the way in, and the vehicle running, can you see fuel dripping in from anywhere?
You are assessing the fuel bowl level by removing the brass plug on the side, right? Not by loosening the top adjustment nut, in which case fuel will flow out with the vehicle running. [again, it's worth asking!]
Carbs are complex. They frustrate the hell out of me. Good luck!
- Regarding the fuel level, it could just be a bad needle and seat. That seems less likely. When you checked it, did you confirm the o-ring was in good shape?
- Did you check the air bleeds on either side of the booster assemblies that they aren't clogged?
- Any idea what fuel pressure you're running at? I don't know if you're running all hardline or if there is a segment of tubing between the pump and carb. If so, you could temporarily tee in a pressure gauge to your fuel line and see where you're running.
- When you rebuilt the carb, did you properly tighten all the components, use the right rebuild kit, and properly install the new gaskets? [it's worth asking]
How do you know you're running rich? With the mixing screws all the way in, and the vehicle running, can you see fuel dripping in from anywhere?
You are assessing the fuel bowl level by removing the brass plug on the side, right? Not by loosening the top adjustment nut, in which case fuel will flow out with the vehicle running. [again, it's worth asking!]
Carbs are complex. They frustrate the hell out of me. Good luck!
Cargo Master
Joined: Feb 2004
Posts: 2,070
Likes: 169
From: Central Texas
If you cannot control the fuel level you will have all kinds of issues. Start there. Get a big screw driver and a 5/8 wrench. You should be able to pull the sight plug out with the engine running and adjust the level to just below the sight hole. If you cannot do that, meaning it won't adjust to correct the issue, pull the needle and seat out and inspect and repair as needed. None of this requires any disassembly as it is all externally accessed. Leaky brass floats will exhibit similar issues.
If you do not understand these adjustments, I would suggests you do some reading. This is probably the most popular carb in the history of mankind (and then some). There is a ton of info for basic tuning procedures of this carb. Good luck.
If you do not understand these adjustments, I would suggests you do some reading. This is probably the most popular carb in the history of mankind (and then some). There is a ton of info for basic tuning procedures of this carb. Good luck.
Fleet Mechanic
Joined: Jun 2019
Posts: 1,899
Likes: 236
From: Southern California
Sunk float. Make sure your float isn't full of gas. If it's one of the composit floats, they can get soaked too. If you have replaced the fuel pump with an aftermarket one then excessive fuel pressure is the most likely issue. Im a full time tech and work on lots of older, carbureted vehicles and have seen that an overwhelming majority of aftermarket fuel pumps are putting out too much pressure. Some just a little high, some high enough to blow past the needle and seat and flood the carb. The pressure needs to be regulated to 3-5 psi, six max.
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