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Discussion Starter #1
Hey guys, I got a rebuilt 302 with a 1850 - 3 holley carburetor that came with the car when i bought it. (before the engine was rebuilt). I'm having trouble tuning this carburetor.

I have read a few threads and they say that these carburetors are only for specific types of engines, does this carb fit my engine?

Secondly the full manifold vacuum line that is supposed to go to the air cleaner is plugged from previous owner. does this effect the tuning? When iam running the car with the choke open and warm i can turn both idle mixture screws in all the way and the engine keeps running and the rpm acctually increases!

I know that you are looking for highest rpm when adjusting the screws but i dont understand why highest rpm is when they are all the way in.

Is there anything to watch out for when tuning this carb?

Thanks guys! I really appreciate any help! Ive been tampering with it for months!
 

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sounds like its been internally messed with. you might want to take it apart and get an idea of the sizes.

first I would address the float level and fuel pressure. holleys tend to be very touchy with these two items in particular.

to me it sounds much too rich. what is your running float height set at? have you messed with this at all?
 

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Discussion Starter #3
Thanks for the response so quickly! Unfortunately I dont even know how to mess with the float. The only things ive touched is the idle curb and the idle mixture.

Its an old carb and i know the last owner had it put on but it looks old as hell. I still have a mechanical fuel pump. How much pressure do I need? Do you know where the float should be set to?
 

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yes, the float should be set to the bottom of the sight plug hole. when you remove the sight plug with the engine running, fuel should be right at the bottom lip, with hardly any leaking out. if it gushes out, you have yourself a very rich condition and the adjustment will be outside holleys required operating settings. this could very well be why it is so rich(turn in the idle screws all the way and acquire a better idle.)

also, if your throttle blades are open past the transfer slots then the carb is already past the idle circuit and into the main metering.

on the subject of fuel pressure, fuel today just sucks. there is no way around it. the old pumps usually run in the 7 to 8 region which really doesn't mesh well with a holley. now with the way that fuel behaves, a pressure reading of 5 psi is much more healthy. anything over 7 starts to blow open the needle and causes flooding.

there is a lot to know on carbs but if I were in your shoes, id start with the curb idle adjustment and float adjustment. start at an idle mix screw setting at 1.5 turns out and play with it from there. every car is different.

here are two of my more relevant holley videos I have made in the past. they may be of some help to you.

https://www.youtube.com/watch?v=hn4...ew-vl&list=PLZTXQG9e2tNwcjjJXZBHkEIrHewEweXBQ
https://www.youtube.com/watch?v=5_lgTTkXJDM
 

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Discussion Starter #5
Thanks so much for the help! Im going to turn the idle curb as far out as i can and then adjust the mixture screws. I will also check the float.

I dont know where the sight hole is or the adjustment but im sure ill find it.

You are right though, it is running very rich. when i accelerate it pushed black smoke out the exhaust.
 

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Thanks so much for the help! Im going to turn the idle curb as far out as i can and then adjust the mixture screws. I will also check the float.

I dont know where the sight hole is or the adjustment but im sure ill find it.

You are right though, it is running very rich. when i accelerate it pushed black smoke out the exhaust.
You have a 4160 style carb. 600 CFM vacuum secondary. It should have around 66 or 68 front jets that screw in, and a 134-9 metering plate for secondaries. It should be good to about 450 HP.

A carburetor does not meter by fuel pressure or fuel level. A properly working carb will actually accept a wide range of pressure and some reasonable change in level without altering mixture at all.

The fuel pressure simply fills the bowl, which always runs at atmosphere. It should be 3.5 to 8 PSI, with 6 PSI as a target. Around 10 PSI and fuel will start to push past the inlet valve and flood. Below 3.5 might fill too slow for WOT.

If you adjust fuel pressure to "tune" the carb, you are messing things up.

The sight plugs are large slotted screws on the sides of the square bowl area. Levels are fairly non-critical so far as how they affect mixture, and you should never tune by level. The carb is designed to have levels just below the sight holes. Be sure the carb fuel level does not "creep up". You should be able to run the pump for long periods with the level set just below the hole and not have it gradually build up and spill out. If level creeps up and runs out, and does not stay just at or below the hole bottom level, you have too much pressure or bad floats or fuel inlet valves.

The high speed loaded mixtures are controlled by main metering jets inside the carb. Your carb was shipped with two front jets and one rear metering plate inside the bowls. Some people drill them out, which really just screws them up. Some people remove the power valves, and that also screws them up for street mixture.

The idle adjustments have minimal effect on running or high load mixture.

Old carbs tend to get hacked up with mods. If hacked up, they can be a PITA to correct. If you have 3-8 PSI pressure and proper float levels, and are running so rich the car smokes, you have to get inside the carb to fix it.

Tom
 

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Old Man gave good advice. Also, being able to screw the mixture screws all the way in without the engine dying indicates a problem with the power valve. If the carb has been tuned incorrectly and a big backfire happens, it can ruin the powervalve. So what I'm trying to say is just because the carb is rebuilt and you would assume they would have put a new powervalve in, the conditions during tuning certainly could have been met to ruin in.
 

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You have a 4160 style carb. 600 CFM vacuum secondary. It should have around 66 or 68 front jets that screw in, and a 134-9 metering plate for secondaries. It should be good to about 450 HP.

A carburetor does not meter by fuel pressure or fuel level. A properly working carb will actually accept a wide range of pressure and some reasonable change in level without altering mixture at all.

The fuel pressure simply fills the bowl, which always runs at atmosphere. It should be 3.5 to 8 PSI, with 6 PSI as a target. Around 10 PSI and fuel will start to push past the inlet valve and flood. Below 3.5 might fill too slow for WOT.

If you adjust fuel pressure to "tune" the carb, you are messing things up.

The sight plugs are large slotted screws on the sides of the square bowl area. Levels are fairly non-critical so far as how they affect mixture, and you should never tune by level. The carb is designed to have levels just below the sight holes. Be sure the carb fuel level does not "creep up". You should be able to run the pump for long periods with the level set just below the hole and not have it gradually build up and spill out. If level creeps up and runs out, and does not stay just at or below the hole bottom level, you have too much pressure or bad floats or fuel inlet valves.

The high speed loaded mixtures are controlled by main metering jets inside the carb. Your carb was shipped with two front jets and one rear metering plate inside the bowls. Some people drill them out, which really just screws them up. Some people remove the power valves, and that also screws them up for street mixture.

The idle adjustments have minimal effect on running or high load mixture.

Old carbs tend to get hacked up with mods. If hacked up, they can be a PITA to correct. If you have 3-8 PSI pressure and proper float levels, and are running so rich the car smokes, you have to get inside the carb to fix it.

Tom
if you think your float level and your pressure do not play a large part then you are a novice.

for everything to work in harmony you need to have the floats set right and the correct fuel pressure. its imperative before any change is made such as jets or secondary springs and so on.

there is no such thing as a carb being good to a certain HP as every carb needs to be tailored to the specific engine, its not slap and go.

if the car puffs black smoke when it takes off it is in the accelerator pump circuit. there is likely too large of a pump shot.

if the OP does get into the jets, he should be running somewhere between 60 and 65 considering his application.

but you cannot tell anything until the floats are set correctly with the correct fuel pressure. try it yourself, go out and adjust your fuel pressure and watch your float level change. anything over 7.5 is blowing open the needle and seat on a hollley as well. adjust your float level and see how it effects the main metering circuit. there is not a single part of a carb that is insignificant or unimportant.

TO THE OP - JUST WATCH MY VIDEOS AND EDUCATE YOURSELF. you should have a better idea afterward of the systems present in your carb and how to tune them.

don't start changing other systems or disassembling the carb until you know the basics are correct.
have a nice day.
 

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Discussion Starter #10
Thanks for all the advice guys! I did watch the videos and today I checked the float level it was almost level with the lip but definitely not pouring out. I then moved on the pull the idle curb back as far as i could. i got it down to about 600. (I was playing it by ear) i tried adjusting the idle mixture screws and the engine rpm increased to about 700 when i screwed them both all the way in and the engine kept running. I suspected the power valve like you have mentioned so i pulled the float bowl off and looked inside, i removed the jets, they are a 57H jet. they look smaller than normal holley jets and i bought new holley non stick gaskets. I removed the metering block and looked at the back side of the power valve, it moves and there are no visible marking or tears on it.

I will try and upload a couple pics for you guys to see.

Thanks all of you again!
 

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just out of curiousity while you have it out, what does the number on your power valve say? Now would be a good time to make sure you have the right one based on the vacuum your cam pulls.

Also, if you hold that fuel bowl upside down the float should sit pretty level. That's a good way to get it ball park.
 

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sounds like someone has played with the secondary idle throttle blade adjustment and they must be pretty open. I really cant figure any other way that the idle screws wouldn't play a factor other than a set of the throttle blades being too far open and its into the transitioning slots. like 95 says, look into the air bleeds and blow those all out with carb cleaner.

I wouldn't think it to be a vac leak either as that would require more idle fuel not less. you have a fun little mystery there sir.

when you slap her back on, be sure to use a new carb to manifold gasket.
 

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Discussion Starter #13
Thanks again guys, so in response to Lizer the power valve dosent have any markings or numbers on it even behind its gaskets (there was 2, is that normal?) The float sits pretty level, its a a bit slanted but definitely not touching the top or in his case the bottom of the fuel bowl.

429,yea i dont understand either.How would I adjust or check that setting? also should i change jet size to the stock 66 size or keep the 57H jets that i found inside? What else should i replace while im this far?

So, so far I have ran the car and found the float to be set correctly. I turned the idle curb back from about 1200 to 600 rpm and when i adjusted idle mixture screws no change in rpm happened until i screwed both all the way in and the rpm increased and the engine kept running. I pulled the front of the carb off and found the jets to e size 57 H and the power valve to have no tears or anything obvious at least.

What should i do next? this is pretty weird ill admit. See the carb was never rebuilt, but I rebuilt the engine myself. If it makes any difference i have this cam shaft. 31-216-2 - High Energy nothing fancy, just a mild cam.
 

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I think I would leave those jets in it for now. they wont hurt you at all. 60s at the highest iwould think for your application. I have a stocker 302 in a truck and I run 54s and its at the correct AFRs.

check back at my adjustment basics video. on the underside of the carb is a small screw that controls the idle opening on the secondary's. if you see transfer slot, then its too far open. if you ever had it idleing at 1200, that would mean the primaries were too far open.

sometimes on old carbs people have drilled holes in the throttle blades. its not all that common, but some rowdy setups need it. make sure someone hasn't done this to your carb.
 

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I would if I were you. the power valve you need is half the man vac. so if you had a vac of 15 you would use a 7.5 valve
 

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Discussion Starter #17
Thanks 429. I think I have found the problem!! When i unbolted the carb from the engine i had to set at about 600 rpm remember? well when i looked under at the throttle plates the transition slots on the secondary plates were not showing. but the ones on the primary were! so i turned the idle curb back even more... when i got it so they were not showing i only had about 1/3 of a turn left until the screw wasnt touching the throttle linkage at all. Whats with that?
is there anything else i should be replacing? i have pulled the carb off and remembered something, i have a square bore intake but it has the partition.. i need an adapter dont i?
 

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love the annular boosters on that other carb. id personally buy it, but I don't think you necessarily need it. the primary idle feed will usually be into the transition slots just a bit. that's pretty normal I would say. usually its the secondary's that get messed up. believe it or not the secondarys are also supplying fuel on your carb. on nicer carbs they have an air fuel adjustment as well. im curious if your getting more from them than you should.

IMO I usually never mess with used carbs. when I do a build I buy a new one so that I know what I have and that it hasn't been permanently altered.
 

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Discussion Starter #20
hmm.. its an option i guess. okay so if thats not the problem then. i dont have the secondary metering block so i dont even think they have an adjustment.
 
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