welcome back to the Junkman's adventures I'm the just man and today we're going to look at this mystifying thing called the carburetor we're going to look at how it functions how each of the parts in the carburetor function and how that affects jetting and hopefully by the end of this video you'll have learned something to diagnose your own carburetor problems what I have here is a rig setup to demonstrate the very basic functions of a carburetor let's identify them using a real heartbreaker this end is where the air filter clamps on or it goes to the air box that's represented here this end of the carburetor would be bolted to the intake that goes to the engine that's represented by the vacuum cleaner hose here this cups what the red dye in it represents the carburetor bowl right here and inside the cup that goes up into through this lump of clay represents either the main jet or the pilot jet because they both do the same thing so I'm just representing one here that goes up into the throat of the carburetor which is represented here and this lungo clay that you see here that's kind of curved also represents as if you could look down this carburetor you can see that this opening it narrows what this is called is a venturi and what we're going to demonstrate here is that the venturi effect and what it's going to allow is that the venturi effect is going to speed up the air as it's going through this tube just as it does in a carburetor it's going to create a low-pressure area up here and because the outside atmospheric pressure is pressing on the water it's going to shove it up the tube and into the vacuum cleaner or in a real carburetor into the engine which is creating vacuum by the piston going up and down also what I have set up here is a vacuum gauge a liquid filled vacuum gauge into a chamber that I built this is actually I built this myself for sinking multi carb engines and I'll explain more about this at the end of the video because it really doesn't have anything to do here all I'm using it right here is to demonstrate that we are pulling a vacuum and I also want to show by creating a vacuum leak which you'll see here in this little barbed fitting that I drilled into the back how that affects your mixture and the ability to pull the liquid up through that little tube and into the engine so let's turn it on and see it work here we are turning on the vacuum and see the needle on the back to engage moving you can also see the red liquid which is water with red food coloring moving up through the brass tube and atomizing within the air moving through our makeshift century here we are creating a vacuum leak and you can see the gauge move as we open and close the valve letting air into and out of the chamber under our first animation as you can see we're at idle speed because the carburetor slide is closed and all the air has to go through that small little channel indicated by the blue line to mix with the fuel coming up through the pilot jet and mixing and going into the intake now I made an entirely individual video on this mixture setting alone you can go find out on my youtube channel so let's move along to when the carburetor slide starts to open as you can see now CarGurus slide is starting to open to allow fuel through the throat of the carburetor to pull the fuel through the pilot jet out the pilot orifice to mix in the throat of the carburetor at this point the idle mixture screw is doing nothing for the jetting of the carburetor now as the carburetor slide opens further still the pilot jet is now flowing in as máxima great and now the jet needle is now metering the fuel through the main jet at this throttle opening so the jet needle Club position is now affecting the mixture at this throttle opening either higher or lower now the carburetor is at full throttle the pilot jet is now not affecting the mixture whatsoever and now the jet needle has opened the main jet all the way so the main jet can flow its maximum flow rate so now the main jet is the only operation that is in play here at wide open throttle well in this diagram we're showing the enrichment circuit also known by some as the choke a choke is actually a butterfly valve that actually limits the amount of air that can flow through the carburetor throat it does the same thing as enrichment just to control the air and not the fuel in this case when the enrichment plunger opens it opens that passageway for air and the fuel to flow and bypass the slide of the carburetor in cold 13 situations now there's another type of carburetor out there the key hen FCR and I'm going to pass this video over to Matt and how to motorcycle repair because he has a good little clip on how a FCR carburetor works with its accelerator pump and it's hot start so I'm going to pass it over to him hey what's up everybody I'm Matt from how to motorcycle repair comm so the junkman has asked me to put together a little video for you guys that explains how the hot start works and also how the accelerator pump works on one of these key NFCR carburetors which is what you find on these four strokes I got on oh six yz250 F over here and got a KTM 450 SXF over there both of them are in four carb clean and jetting so let's take this over to the workbench and I'll show you what it's all about alright guys so here's the whole mechanism that operates the accelerator pump basically here's your throttle that your tables move this is your throttle wheel and there's a cam on the backside of this and it pull pushes down on this this arm here basically there's a rod that runs down here and pushes on a diaphragm and then it squirts fuel inside the intake so let's go ahead and give it a squirt so that's how it works alright so why do you need an accelerator pump well basically these high-performance engines have large carburetors you whack the throttle open right you get this rush of air causes a lean condition and to compensate for that you have an accelerator pump which covers covers up that lean bog and basically that's that's how that works alright guys so the hot start is basically a plunger like this it's cable operated and you want to use it when your bike is really hot it won't start or if you dump it in a turn and you pick up your bike and its price pill fuel inside the intake tract and it's too rich to start so you need to lean it out that's basically what this does it's a plunger that moves explores exposes a port and allows more air to get into the fuel-air mix cleaning it out so this guy like I said is cable operated it sits in here in the top of the carb and there's a port here so it's when it opens it'll draw air from under the top carb cover here and it dumps it right here ahead of the slide so it basically it's basically a vacuum leak you're introducing air into the system in hopes of Leaning it out and getting your bike to start all right guys well I hope you enjoyed that video hopefully the junkman can link to a playlist that I have that has about 10 videos that will help you with the four-stroke carburetor all right guys see you in the next video well I hope you learned a little something in this video about carburetor jetting and how a basic carburetor functions this is universal across many different types of carburetors they all have the same kind of circuits and once you understand what each circuit does you can get your motorcycle or find out where and what adjustments you need to make to solve a problem within that throttle opening range so until next time I'm the junkman and like my facebook page check out my Twitter subscribe and also visit some might fill out links they help pay for this content and so I can create more but of course you never have to do that just come on back for the next video and thanks for watching