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How does CV carburetor work animation DIY adjustment screw - ep26 - Roma Custom Bike

Feb 14, 2022
In this episode, I will fulfill one of your requests: the mixture

screw

adjustment

on a CV Carb Hi guys, I am Custom Cez for Roma Custom Bike and it is my privilege to bring you this first episode where I try to address your requests: today we are going to find out what the mixture

screw

on a CV

carburetor

is and how to adjust it. A while back I posted the “CV Carburetor” video where I took my carb completely apart and after a good clean I adjusted the float and used a rebuild kit, the link is in the description.
how does cv carburetor work animation diy adjustment screw   ep26   roma custom bike
In the weeks after the video was released, I received many messages, some of thanks, and I am very grateful for them, but also some messages with advice on how to do it better and some pointing out what I did wrong. Among these messages, the most frequent request has been if you could shed some light on the mixture

adjustment

screw. So this brings us right now, where I will do my best to quench your thirst for knowledge on the requested topic, but first, let me correct some of the mistakes I made in the previous video. One of the comments was from an Italian friend SteenNoice Garage, he suggested blowing out each hole and each jet with some compressed air and using a thin metal wire to make sure each hole is clear of any debris, dirt, or even used cleaning products. in this very process.
how does cv carburetor work animation diy adjustment screw   ep26   roma custom bike

More Interesting Facts About,

how does cv carburetor work animation diy adjustment screw ep26 roma custom bike...

I immediately thought a used metal guitar string would be perfect, but probably a single strand from an old brake or clutch cable would be just as good. I also received feedback from CV Performance's own technician who pointed out a very significant problem with the procedure I showed in the video: he pointed out that the method I used to replace the diaphragm in the slider assembly was absolutely wrong, on some models. the two are actually glued together, so pulling on the diaphragm will only result in ripping it. That's not all, after the comment I rechecked things and noticed that the joint between the slide and the diaphragm was a bit loose and I highly doubt it was a tight joint.
how does cv carburetor work animation diy adjustment screw   ep26   roma custom bike
So i proceeded to go to the cv performance site and bought a complete slide and diaphragm assembly just to make sure i didn't have any issues later on. I suggest you do the same, go to www.cv-performance.com and you will find all the parts you may need to rebuild your carb. The link will also be posted in the description. I want to thank Stenn Noice Garage and Cvperformance for improving this program effectively, I invite everyone to do it and I want to thank all the people who have commented and posted suggestions on the videos, so thank you very much.
how does cv carburetor work animation diy adjustment screw   ep26   roma custom bike
But now let's get to the new thing: the mix screw! Why do you need an adjustment in the first place? Because this screw determines how much fuel will be mixed with the constant supply of air in the idle fuel supply circuit. Simple truth? No? Didn't you get it? Well then, let's see how the carburettor actually

work

s and I think everything will be much clearer. At the bottom of the carburettor we have the float bowl, always filled with gasoline thanks to the action of the float and the fuel valve. As the fuel level drops, the float opens the valve to bring it back up.
In the upper part of the

carburetor

we have the jet needle, the piston or vacuum slider and the diaphragm. The entire assembly is held in place by the spring. Then we have the butterfly, controlled directly by the throttle cable. And finally we have the Pilot Jet... and the Main Jet, both feeding the two fuel circuits inside the carburetor. Last but not least, the fuel mixture adjustment screw. Now how

does

it

work

? Under idle conditions, fuel is drawn from the fuel container through the pilot jet and mixed with air before entering the cylinder. The entire process is powered by the low-pressure vacuum that the piston creates inside the cylinder.
When we turn the throttle, we directly affect the throttle valve, which opens. Now the low pressure is beginning to affect the upper vacuum chamber as well. The diaphragm is sucked in and with it the slider and jet needle rise. As the jet needle rises, its conical shape allows more and more fuel to be sucked through the main jet. As the slide opens, more air passes through the carburetor, proportionally to the amount of fuel. While we're at it, let's see what happens when we pull the choke knob. Opens an additional stream of fuel directly into the cylinder, enriching the mixture for easy starting on a cold engine.
Let's go back to the idle circuit so we can take a closer look at the mixture screw and how it works. By turning the screw, we open and close the fuel passage, thus adjusting the ratio of fuel to air in the idle circuit. When we twist the throttle, the main jet

does

n't start supplying fuel immediately; For a short period of time, the idle jet remains the only fuel source for the engine, which is why the mixture is set too lean or too rich. will directly affect the responsiveness of the engine. You should know that this adjustment is affected by altitude, fuel type and humidity, as well as the installation of different pipes or air filters.
So knowing this procedure can be useful not only for those of us who like to modify our

bike

s, but also if you simply decide to take your

bike

with you to the mountains or the beach on vacation. To remove and re-install the carb on the bike you can follow the original video, as usual it will be linked in the description. However, I have removed the carb so I can show you exactly where the screw is located, on the lower right hand side between the fuel bowl and the manifold opening. I have the stock Harley Davidson carb that came with this bike, but this process can be applied to just about any CV carb out there.
The only major difference you may find is that some carbs will have the screw located on the opposite side of the carb body, between the bowl and the air inlet. In this type of setup, the adjustment screw regulates the amount of air in the mix. In my case, with the screw that regulates the flow of fuel, we turn the screw clockwise to lean. and counterclockwise to enrich the mixture. On other carburettors, where the screw manages the airflow, we will do the exact opposite. Just to be complete, if your carb has never been adjusted, you will have a factory plug pressed into this cylinder that blocks your access to the adjustment screw.
This is just a simulation, but you can remove it by drilling a small hole and prying it out with a self-tapping screw. Just make sure you don't drill too deep and damage the screw, as the channel is only 6mm deep. Before I go any further I would like to thank you as always for your support, this is an independent production so we need all the help we can get to keep bringing you quality content. Please click the like button, share our videos on your social networks so we can reach more people and visit our site www.

roma

custom

bike.com and see the new accessories we are producing, such as exclusive new

custom

running boards for many models of Harley-Davidson. , along with the t-shirt from the show because nothing works better than sharing in the real world.
For US orders we ship directly from our Boston location, for the rest of the world we ship from Italy. Thank you very much and let's get back to work. Now that we have access to the screw, using a flat head screwdriver, we turn the screw clockwise until it seats smoothly. While you do it there are two important things to remember: 1st) do not force the screw because it is very fragile and you could ruin it and then you are the one who is "screwed" 2nd) you have to count how many turns it takes for it to seat smoothly.
So let's count: 1/4, half, 3/4, etc. This is so, if we want to go back to where we started, we know how many turns it does from a sitting position. In my case a little more than 1 turn and 3/4 Now, from the seated position we return 1 turn and ¾. that will be our starting point to begin the adjustment. However, we first have to reinstall the carburetor on the bike, because to do this procedure, the bike must be running. We are going to use a normal screwdriver for this procedure, but if you feel you will need to do this often, there is a kit on the cv performance website that makes the process much easier.
To make the adjustment, the engine must be nice and warm. I start from this situation, typical of a carb that needs serious help, coughing and slow throttle response. So, let's try to fix it! I start by turning the screw clockwise, this reduces the amount of fuel flowing through the system and therefore leans the mixture. The engine will stumble until it shuts off. Now I go back to the starting point of 1 ¾ turn and try to turn counterclockwise. Let's see what happens… The goal is to adjust the screw so that we get the highest rpm at idle. Since the airflow is constant, we will try to get the best and most efficient air-fuel ratio for our engine.
By turning the screw clockwise we are letting more fuel through the system and as you can hear the engine revs... This seems to be the point where we have the highest rpm... I'll add another Half a turn but I can't detect any noticeable difference so I'll go back to the point where turning stopped making a difference. Let's twist the throttle to see if it's responsive enough or if we still have some doubts. As I mentioned, the goal is to have the most rpm at idle while still having fairly responsive throttle control. So by moving the screw back and forth in very small increments and keeping track of the turns, while twisting the throttle, you too can find where your bike works best.
You should note that if after 3 turns counterclockwise the rpm's are still increasing it means the jet is too small and needs to be replaced with a larger one, on the other hand if your setting sounds good with less one full turn of the screw. , probably the jet is too big. It takes a bit of patience to find the right setting, but it's worth it! If you find that you can't adjust the mix correctly, I suggest checking that all the gaskets are seated correctly and that the connections are airtight. For example, check between the manifold and the two cylinder heads or between the manifold and the carburettor.
An air leak at any of these points would de facto lean the mixture, compromising any adjustment, jet size, etc. If you plan to do this adjustment in your garage or in an enclosed space, you should get a pump system to get rid of the exhaust or you'll risk suffocation or CO2 poisoning, to say the least. What I did was I took an old kitchen fan from a restaurant, a rather beefy one, and I locked it in a wooden box. I made the box airtight with the help of some silicone. I then took some flexible aluminum conduit that I bought at the local hardware store.
I attached one side of the aluminum conduit to the box using high temp tape to secure it in place. I attached the other side of the hose to the muffler and with the help of more high temp tape and foil made it fit quite nicely. By doing so I made a decent exhaust suction system. All absolutely DIY. Obviously the fan unit needs to be placed outside; otherwise it is completely useless. generous today, visit our site www.

roma

custombike.com and check out our shirts and new accessories for your bike. I'm Custom Cez for Roma Custom Bike and see you in the next episode.

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