Holley Carburetor Tuning: Idle Circuit Mods for High Duration Camshafts

Randy here uh I know guys it's been a while but we tried to get everything straight now here we can shoot some of these videos I promise no one on the idle circuit and here's part one of it now we got a 4150 double pumper that I'm going to show you the video on but this carburetor is no different on my own surface as this carburetor right here this is a 1850 vacuum secondary so the secondaries are worked off of a diaphragm okay here we go we got the 4150 here what I want y'all to do is this is the first step to correct the idle circuit if it's run rich and these metering block screws are not making holy any difference in the mixture the adjustments you can turn them all in it don't make much difference this is the first step to present now what we're going to do is what I want y'all to do is just crank your mother woman up get it Island the best you can it where I was the best to speeding off then cut the motor off take the carburetor off and what we're going to do is look and see how much of this transfer slot this long slot here is exposed without touching the idle changing the idle speed at all just like it come off your car we want to look at these transfer slots and we don't want that about forty thousand six posed right around there you know you go down as low as thirty or maybe up as much as sixty but we probably got almost eighth of an inch here that's way too much now what happens when it gets this much exposed is pulling all the fuel mixture and I don't through the transfer slot and hardly none through the auto slot now when we bring this mixture I mean this idle speed down we're going to actually unscrew it here and get it down to right about where it should be right about here you see the difference in the actual how much is actually exposed on the throttle plate you can see that transfer slot now when we got probably 40 fifty thousand six pose now we're going to be pulling less fuel out of this slot and more at the actual outer port and this is the actual out of port okay right here that is the actual out of port this is a transfer slot which is part of your port and it transitions from your idle to your main well to your main jet it helps the the in-between before it starts pulling out of the booster that right there is going to let it pull a little more fuel as you're pranking the throttle is pulling more fuel right there now when we got that much exposed here or what we first showed it very first before I changed it we need to take and get more air by passing these taller plates and the best way to do this and you gotta be kind of careful is to take this is a different little different product plate but it's still gonna work same way we want to take them on the idle circuit side which is on the same side of the butterfly as the idle circuit come in just about like these about a quarter of an inch of inward or maybe 3/8 of an inch in word just get it away from the right at the edge so right here is a good area and we want to start off maybe drilling us up seventy to eighty thousand hole right there all four of them remember they want to be the hole needs to be on the same side as the idle circuit as your Forks are you don't want a man board you want them outboard alright and when you do this what he does is it allows air to bypass more air to bypass this throttle plate through these holes and it lets you close the throttle plate down because your idle will come up because it's bypassing air so you brought this screw backwards counterclockwise and that's when is actually let me switch throttle plates here it's going to start coming down and looking like this it's going to look like you've only got about 40 or 50 thousand maybe thirty five thirty it doesn't matter loans we don't have get it there above seventy thousand sixty-five seventy thousand satisfied the max I like to see so when you do that then all of a sudden we're pulling fuel now more fuel out of the idle surface and logic transfer slot and when you do that you're going to get your adjustment back here now I'm going to show you I'm going to show you where the actual mixture comes from it actually draws fuel from right here which is kind of hard to see guys from the main well here across to a little office here of that office there's a tube here for the idle circuit and it comes out right here and then it travels down a metering block and this hole is actually lined up with the transfer slot so the transfer slots pulling fuel out here and then the actual mixture screw is pulling fuel across to this hole which in turn lines up with these this is the transfer slot and this is the idle mixture hole so these is pulling is pulling air out of this bleed here in here which is right here on the metering block guys stupid Stephen right here's where the air is being sucked out of this air bleed on the front and it's drawn fuel right here out of here so they're almost right together drawing fuel and air so it's emulsifying as it comes down and it gets to the transfer slot here's the transfer slot it's actually this hole right here alright now when we change this mixture screw this mixture screw always letting is you'll go from here to right here so it transfers to the idle circuit here it comes down this to the actual transfer slot and then it comes across to the actual oil mixed report and this is where this screw right here is adjusting between here here is adjusting how much can transfer through here so what happens is when we get too much coming down here and we got too much transfer slot open here open xposed on the throttle plate is drawn all the fuel right here so when it draws so crossed here tries to draw it across here it's not making any difference you got too much fuel flowing here and here but when we we actually close this transfer slot off right here and it's not got much coming through here we don't have much we don't have much actual fuel coming through here with that transfer slots only got a little bit exposed so then the majority of the fuel has to come to this island for right beside right there so that's why we don't have no idle mixture adjustment is because it's all been is coming out of this slot because it's too wide it's open like so and almost all of its coming through the actual transfer slot when we close that up then all of a sudden we got adjustment we got our mixture adjustment back on our throttle plate right here with the screw because it's coming across here and draw most of the fuel through the actual idle port instead of the transfer slot the transfer slot is part of a dial circuit it's going to draw a fuel to there just like I said what is it when it's got too much exposed right here it's going to draw all the fuel here in this it's just so much that you can't control the fuel through the idle slot you cannot so when you close it down by drilling these four holes in the butterfly start off with a fika 70 80 thousands drill bit and drill your four nice little holes don't don't press down hard on it just take your time and put your four nice low holes there and then if you need more if you crank it up you're just a mixture and you see it start adjusting better and then when you get to adjusting it all getting engine hi get the mixer just at the idle speed then let it cool off take your carburetor back off check it again and see what yeah if you're in that 35 to about 65 thousands of the transfer slot then you're in there not drill it a little bigger and each time you're gonna notice the throttle plate closed up Matt yeah get a little smaller less transfer slot here exposed and that will be the first step to fixing your idle circuit now we're going to go in-depth another there's going to be a part two where we I'm going to show you how to to actually control the orifice the fuel flowing through the office on the idle circuit will actually get into putting a little little bleed in there I'll show you how to do it with a would put some threads in the metering block right here and will actually will actually put put bleeds right here guys rip it let me get a better picture where you can see this and we're going to actually put a actual little screwing bleed right here that's not hard to do guys it just takes a little getting used to don't be scared of doing it if you ain't sure then try gonna try to get an old meter block that you can just try first to get it in there but will up get into that on the next video but this is under this is going to fix a lot of them this is going to fix a a bunch of problems with idle circuit I can tell you once you get that that transfer slot only maybe 40,000 six-phase then you're going to see the actual mixture start adjusting in if you don't then off I'll cover that in the second video but it it's going to make a difference alright guys this now this will work on this 750 double pumper 850 650 on the the vacuum secondary carburetors like this 1850 it works same way on there guys the same exact way you'd see this has already been modified you can see the four small holes and do all four barrels when you do it do all four butterflies and this is the first step to get you out of right and then next video we'll get into actual restricting the fuel and changing the actual air bleed size which will between all them you'll you'll be on the money and and this might get you right on the ballpark to start with and you might not have to make anymore changes now we will get into different we're getting a lot of videos on the carburetors guys that y'all like it I know it took us a good while to get back with you but be patient we're going up we're going to start doing a bunch of videos hopefully hopefully start doing three or four week and I'm gonna try to cover everything and if there's something I'm not covering that you're not sure about if you can let us know we'll put it in the video and I guess that's about it guys that's about the whole deal and uh to start with that's part 1 of title circuit this is Randy and uh we'll catch in the next video

Channel: Racing and Automotive, How to's and advice

Views: 233,386

Keywords: National Hot Rod Association (Organization), NASCAR (Organization), Drag Racing (TV Genre), Engine Masters

Id: JDPwY0LbRVY

Length: 12min 2sec (722 seconds)

Published: Sat Oct 17 2015