How to tune a moped carburetor
Com Scoot F. How do I tune the carburetor? Please read through this entire section and any other links or documents necessary to be comfortable with the idea of tuning before you start fiddling with any part of the carburetor. Your experience is more likely to go smoothly if you make yourself aware of the entire process beforehand.
To speed up the search for specific information, below are links directly to each section of this page. Trial and error tuning for power is my preferred method, and it's the one that I'll be covering in this article in more detail. Trial and error tuning is what it sounds like.
You'll be trying a selection of jets in order to find out which ones work well and which ones don't. Recording information from each test should allow a pattern to emerge, pointing you toward a suitable jet for your application. Most forms of tuning involve at least some degree of trial and error.
Spark plug reading is another popular tuning technique. It generally involves using a new spark plug with each main jet, so it can get a little expensive. For our CVT driven scooters, you usually have to brake and slow down quickly, being careful and mindful of your surroundings, so the clutch disengages and the engine will no longer be rotated by the CVT.
Then the spark plug is examined to determine if the mixture is correct or not. Sometimes the plug is chopped up so the whole porcelain section is visible. Sometimes tuners examine the plug with a magnifying glass and light or a specialty plug viewer. Knowing exactly what you want to see can be tricky, and improper spark plug heat ranges can throw off results.
I feel that spark plug reading is best left to experienced tuners or used in addition to other methods. In it's most basic form, tuners simply check for wet, dry, dark, or light spark plugs to point them in the right direction if other symptoms aren't giving them a clear indication of the direction they need to go with jet size.
If you'd like to learn more about reading spark plugs I have some information HERE and you can find a lot more information using your favorite search engine. Most likely you'll be looking for readings somewhere between and As with any other method, choose the largest jet that works well.
Example 1 : You started with a 95 main jet and max speed averaged 41MPH. You switched to a 90 main jet and avg max speed increased to 43MPH. You would want to try another smaller jet, like an 85, next. You would want to try another larger jet, like anext. Example 3 : You started with a 95 main jet and max speed averaged 41MPH. You switched to a 90 main jet and max speed decreased to 37MPH.
Carburetor help, jetting, and tuning help:
You would want to move in the opposite direction. Skip over the 95 main jet that you have already used and move up to a main jet. Skip over the 95 main jet that you have already used and move down to a 90 main jet.Here is a table made from the formula: the temperature and altitude with give you the correct atmospheric pressure, the numbers below have been pre calculated. This will give you a good place to start.
At this point you can do a plug chop to verify jetting. Be sure you are full throttle under load for at leased yards or so. Up hill works best. If the motor is back firing at decel this is a good indication the pilot jet is to lean. Try richening up the fuel mixture by turning the fuel screw out or the air screw in to allow more fuel.
Any more than 3 turns out go one size larger on the pilot jet. Fuel screws are towards the front of the carburetor and air screws are toward the rear of the carburetor.
In most cases screw adjustments won't correct the lean back firing, installing a one size larger pilot jet will do the trick for higher elevations Colorado. Take 0. If it is 80 F at ft, you calculate a new CF, say 0.
This gives you a good place to start your fine tuning. Needles are a little trickier, I think each needle clip was worth a change in CF of 0.
You can also use it for pilots, but pilots sometimes go the other way larger at high altitude. You need to determine this by pilot screw position. Another way is by backfiring on a YZF on decel, too lean. Richen up by turning pilot fuel screw out. I have the formula at home, I will get it and post it. I made it into a table and pasted it on the inside of my toolbox lid. Remember, its a good place to start but is not the same as jetting by someone who is good at it.
For example humidity can affect jetting and the formula does not include this. This is your correction factor at standard temperature and pressure STP.Learning How to tune your carburetors for a new exhaust as well as other bolt-on modifications, will set you apart from anyone else on the street.
Never stop gaining knowledge and understanding of the things you love. So you have been enjoying your bike for months now or maybe you just purchased your first. You may have heard that in order to allow the changes you have made to be effective, there may need to be some carburetor tuning done to keep the run-ability of the bike as responsive and effective as it was before your upgrades were made.
I want to share with you a fast and easy way to make these changes to your bikes carburetor after a new exhaust has been installed at a MUCH LOWER COST than buying expensive jet kits that may end up putting you in deeper water than what you planned for.
So in this post, I want to really hone in on the tuning aspect of your carburetor as well as drop some fundamental knowledge bombs on basic principals to follow that will help you become fully prepared and confident in your upgrades when it comes to tuning your carburetor for your exhaust.
If you would rather push on to the steps, be my guest! Just scroll down. Your exhaust systems main function is to get rid of the spent or burnt combustion process from the compression stroke as effectively and efficiently as possible.
What you are hearing is the aftermath of the contained explosion going on inside the combustion chamber. Typically most standard exhaust system will have stages in the exhaust where the pipes diameter changes as its makes its way towards the end of the tailpipe. As exhaust leaves the combustion chamber, through the exhaust port and into the first bend or section of the piping it expands and slows, developing pulse waves of both the burnt gasses and sound waves as it makes its way down the system.
Once that wave makes its way into the larger portion of the exhaust which is typically the muffler it slows down again as it comes into contact with different packing materials such as BAFFLES. What you hear is the end results of that sound waves final push out of the system. The exhaust gas leaves that exhaust port at a very fast rate then quickly gets restricted by the diameter of the pipe and stays pretty consistent to the very end.
No baffle to slow it down and change the pulsing sound wave or dampen the noise. There is also no muffler to add even more resistance. Resulting in a very loud and quick pulse wave. There is a huge science behind exhaust fabrication to achieve different levels of performance from the motor.
The issue with a lean mixtures is that it causes higher heat temperatures throughout the engines working parts. Everything from head gaskets, cylinder gaskets, cylinders, pistons, valves, exhaust parts and even into your fluids like the coolant and engine oil are now being heated and over worked at temperatures that can cause them to fail, deteriorate and warp over long periods of use.
Ever seen a pair of headers or a section of the exhaust pipes that have changed colors? Overheating metal in anyway, causes it to react in different ways. Since your motor already operates at high temperatures, it is important to not make matters worse. Fuel actually acts as a cooling agent as well as the main ingredient to your engines BOOM. Crazy right? You may have notice that the main jets are two different sizes. The rear cylinder runs hotter then the front cylinder since it is getting hot air pushed on it from the front cylinder and they are most of time tucked in close to backbone of the frame.
They use a bigger main jet in the rear to help cool the cylinder down. Genius design and it works perfectly.Carburetor adjustment does not require an engineering degree, but some mechanical ability is necessary.
Whether it is a stock or aftermarket carburetor, you will need to consider the temperature, altitude and humidity as these can have an effect on how well it is set up. These environmental factors determine how the fuel-to-air mixture runs through the carburetor. For example, in a higher altitude there is less air for your motor and the fuel-to-air mixture will be richer. Thus, your carburetor will need to be adjusted to accomodate less air in the atmosphere.
Adjust the idle speed by locating the small spring-loaded screw which is usually located next to the throttle control. If you have a tachometer, turn the screw until you reach an idle speed between and rpm. If you do not have a tachometer, set it for a low idle speed; not so slow that the engine stumbles or stalls, but not so fast that the clutch won't try to engage and move the vehicle forward.
Adjust the fuel-to-air ratio FTA by locating the slotted idle mixture screw near the air-cleaner side of the carburetor. With the engine off, turn the screw all the way in counting the number of turns it takes. This is your baseline, if you are not happy with the adjustments. Turn the screw back to the baseline, start the engine and let it warm up for five to ten minutes.
Count how many turns this takes. Divide this number in half to find out where the optimal point is. Turn the screw in that number of turns. You may have to go back and adjust the idle speed screw if the idle is now too fast. Based in New Jersey, Tamara Walton has been writing articles and poetry since Her articles have appeared in "Bowhunter" magazine and her poetry in anthologies published by the Library of Congress.
How to Tune a Carburetor on a Motorcycle
Items you will need Screwdrivers Carburetor needle Tachometer. About the Author. Photo Credits.See also: PHBG tuning made easy a step by step guide. First, you need to install a clean air filter. Second, you need to insure the float level is properly set. If the gasoline level is set too high or too low, properly jetting your bike will be impossible. A high float level will cause it to run rich and a low level cause it to run lean.
PHBG's always seem to come level, but its good to check.
Finally, make sure to start with a fresh spark plug when tuning. Once you reach WOTthe amount of gas is completely controlled by the main jet.
Look at the chart see how it is moderately effective all the way through. That is because it uses a separate jet which also sucks fuel that doesn't have a needle. The adjustable screw that is flush with the carb body controls it. By turning that counterclockwise you will let a just a tiny bit more gas flow in to the system, and by turning it clockwise you will cut that off.
So you can make very small adjustments by using the screw, or you can make major adjustments by changing the jet. Here is image orignially submitted by a Dutch Tuner, and updated by I. Think of the clip as being stationary and the needle moving up and down along it like a window sash. The higher it is the more open and therefore richthe lower it is the less open and therefore lean. Elliot seized his Polini by leaning out his needle.
PHBG carbs do not always come with the same needle stock, so it is important to check your needle before installation of the carb. The needle is stamped onto the needle right below the clip notches. You should refer to the chart below when sizing needles. If your carb did not come with a W6, W7, or W9 and you are having a lot of tuning problems I would suggest starting with a W7 and work from there. As stated previously, a good place to start is with the needle clips.
Raising the needle by putting the clip in a lower notch will richen the midrange mix, and lowering the needle by putting the clip on higher notches will lean it out. If you find the bike responds poorly on all notches or only runs okay on one of the very outside notches, you should look into getting a different needle.If your moped has been sitting in your garage or storage room for the past few months, it may be time to give it a good tuneup before your next ride.
Tuning up a moped can increase its speed, fuel efficiency and improve its overall appearance. Luckily, tuning your moped only requires a few simple tools and should only take about an hour to complete. You should be back on your bike enjoying the road in no time. Replace the spark plug in your moped. Although it may still be working, it's always good just to replace it and have the old plug as a spare. You can remove your spark plug by using a large-sized wrench, placing it over the spark plug body and turning the plug to the left.
Clean the entire fuel system and replace the fuel filter. This means checking and cleaning the following items: the gas tank check for rust or leakagethe gas line check for leakage or cracks and the carburetor give it a thorough cleaning, using a wire brush to get the grime on the inside and outside of the carb. Take the battery out of your moped, if it's so equipped, charge it up with a battery charger, clean the terminals with a wire brush then reconnect it.
Check the fluid and oil levels, if your moped has a transmission, to make sure they are both full. Check the tires for tread depth. Check for cracks, leaks or pinhole-sized openings in the tires. Blow them up to the recommended air pressure and listen for any leaks. Turn on your moped and, with the kickstand down, let it run in place.
Check all of the electrical workings, such as the brake lights, turn signals and battery, to verify operating condition. Accelerate your moped and check the brakes for appropriate stopping response.
Give your moped a good wash. Simply use a rag and some water to wipe down all of the engine parts, bike frame and handlebars. Giving your moped a good wash-down not only improves its cosmetic appearance, but it can also improve your engine efficiency since there will be less grime for the engine to handle.
Check your vehicle's tags and make sure they are up-to-date. If you have a three-year moped sticker, make sure that it has not expired. If your state requires a license plate to operate your moped, make sure that the tag is for the correct year and that your vehicle's insurance is up-to-date.
Grab some handy tools and place them in the storage compartment of your moped. Start it up and take your moped for a spring ride. This article was written by the It Still Runs team, copy edited and fact checked through a multi-point auditing system, in efforts to ensure our readers only receive the best information.If it does go out of adjustment lots of things can happen.
It can make the scooter hard to start, it can make the scooter slow to accelerate, it can cause the scooter to idle badly and stall or it can make the scooter idle fast so that it's trying to go all the time and needs the brake to hold it stationary. None of these things are good. What the carburetor does is regulate the amount of fuel and air which are supplied to the engine.
To go faster you need more fuel and more air and they must be in the right proportion. The fuel also has to be atomized as much as possible i. The carburetor controls all these functions and generally does it quite well. The type of carburetor used on most cc GY6 type engines is a Keihin style CV carburetor with a 24mm throat. Keihin design carburetors are a well tried and tested design developed in Japan Keihin is a region near Tokyo.
Without removing and disassembling the carburetor, there are only two adjustments you can make, but these should take care of most minor problems. The first is the adjustment of the idle speed. Above is a picture of a typical GY6 engine carburetor and the view is that from the right side of most engine configurations on cc Chinese scooters.
There's a small spring loaded screw which adjusts the idle speed. It's right next to the throttle control which is connected to the twist grip on the right handlebar. On most cc scooters, idle speed should be around rpm when the engine is fully warmed up.
Don't make adjustments when the engine is cold. Take a 5 or 10 minute ride first. When the engine is cold the automatic choke is in operation and that can change the idle speed. If you have a tachometer, setting the speed is easy.
If you don't, you want to set the speed to a low idle. Fast enough so that the engine doesn't stumble or stall, but slow enough that the clutch doesn't engage and try to move the scooter forward.
On most scooters from 50cc to cc, this will be somewhere in the rpm region. This is done on most scooters using a screw adjustment on the other side of the carburetor as shown below.