About the Air Screw Adjustment

Michael Forrest /

ADJUST AIR SCREW FIRST

The idle mixture hole is at the bottom of the carb throat just below or in front of the front edge of the slide (if it were allowed to close fully). This means the idle mixture is always part of the whole mixture no matter what the throttle position is. That is why all carb adjustments begin with the idle adjustment (air screw and possibly changing the idle jet).

Adjust It:

With the engine warm go ahead and adjust the air screw till you have maximum idle RPM. If it is really high for idle RPM then lower the slide a bit by unscrewing the slide stop screw. Then turn in the air screw 1/2 turn so that the RPM lowers a bit. The idea here is to have the idle mixture a bit rich to offset the instantaneously lean mixture that results from cracking the throttle open. When the air screw is set right then the engine exhibits a nice crisp acceleration from idle, both with the transmission in neutral and while riding. You don’t want it so rich that the engine sputters any while riding at slow speed with the throttle closed or just barely open.

When to Change the Idle Jet

If the final air screw position is more than 2 turns out then you need a smaller idle jet. If the air screw position is less than 1 turn out then you need a larger idle jet. Until you get hold of another jet just stick to the air screw adjustment that you got when following directions above.

Adjust Before Each Ride

If you live where the humidity/temperature changes a lot from week to week then you should adjust the air screw before each ride. This adjustment will help correct about 1/5th the overall jetting throughout the whole throttle movement. Like I said before, the idle mixture is always fully on no matter what the throttle position. So if some hot humid weather comes then adjust the air screw out. Of course you should still change the idle and main jet out for each major seasonal change but still by doing this little trick you can have a happier engine each time out. And a happy engine means a happy rider!

Re: About the Air Screw Adjustment

Probably Fred /

> Michael Forrest Wrote:

> -------------------------------------------------------

> ADJUST AIR SCREW FIRST

>

> The idle mixture hole is at the bottom of the carb throat just below or

> in front of the front edge of the slide (if it were allowed to close

> fully). This means the idle mixture is always part of the whole mixture

> no matter what the throttle position is. That is why all carb

> adjustments begin with the idle adjustment (air screw and possibly

> Adjust Before Each Ride

>

> If you live where the humidity/temperature changes a lot from week to

> week then you should adjust the air screw before each ride. This

> adjustment will help correct about 1/5th the overall jetting throughout

> the whole throttle movement. Like I said before, the idle mixture is

> always fully on no matter what the throttle position. So if some hot

> humid weather comes then adjust the air screw out. Of course you should

> still change the idle and main jet out for each major seasonal change

> but still by doing this little trick you can have a happier engine each

> time out. And a happy engine means a happy rider!

You are as dumb as a box of rocks, I have almost 200k mi on two-stroke bikes that I ran or raced,

you’re posting most of the stuff that you learned on the Internet and or a few miles at a time once or twice a year but you’re so inexperienced as far as mi goes!

I have a-lot of 2 cycle enduro bikes and moped experience that you Will never have you have cause you’re confined to a shit hole country but United States is wide open Plus I have hare scrambles/finisher pins in almost every 8 mile course I ever was in and I’ve never change the settings of my single cylinder factory 100 to 400cc bikes ever unless exhaust or customer required changes,

where do you make up all this stuff ? I know because you will never know nothin about a two cycle engine if one dropped on your head ! And I hope it’s soon !

factory jap settings are good for 30 f to 80s F

I love the carb factory settings, with stock factory airbox on Japanese enduro bikes for all round riding,

why would you change anything! Oh ya I why know why because you wouldn’t know a 2t engine if one hit you in the head!

Re: About the Air Screw Adjustment

You two are friends and are just playing around right?

Re: About the Air Screw Adjustment

Actually Michael , Ken has a point. I know u spend alot of time on various complex calculations to flesh out two strokedom. But I just read your profile and dude ...we want to see your bikes. The don't have an actual licence stuff is too unbelievable without a decent explanation that for all intents and purposes , I must think that maybe there are no bikes in your life and you are the Steven Hawkins of mopeddom. Which dude, is ok with us if stated. So please provide proof. While u r at it some pictures of the actual you next to or on the actual moped/ mopeds that fuel your passion. Otherwise please let it be.

Re: About the Air Screw Adjustment

Michael Forrest /

Hmm, such resistance to basic physics/science. Any one who is good at 2 stroke tuning knows the weather dictates the needed jetting. There is tons of info on this topic so I dont feel like I have to prove it here because it is just a fact. And I have owned at least 10 motorcycles since I started riding in 1973.

Notice that the biggest bitchiness here was from someone who had not one single fact to counter what I wrote. He basically just said I am all wrong. Carb tuning is not for insensitive people who think bikes are all OK till they die. It is a fine art.

Just use the same method for setting the air screw and notice how that setting changes with major weather changes (like from season to season). That will be proof of what I am saying.

This is just info for beginners but obviously there are some sub-beginners on this forum. And they are unnecessarily rude. What ever happened to common courtesy? If you disagree with someone then state your reasons without degrading the other person. The facts will speak for themselves and every one else can make up their mind who sounds more reasonable. Every one has a right to an opinion but no one has the right to unnecessarily insult other people just because they disagree with them.

Re: About the Air Screw Adjustment

Michael we aren't doubting you we just want to understand whether you come to this entirely from a virtual orientation or if u actually ride and build them. That's all I for one seek clarification. I'm aware of your you tube videos. But at some point I need to see something metal.

Re: About the Air Screw Adjustment

Michael Forrest /

Marc I have been building/modifying bikes for over a decade. I started with many porting changes on my KDX200 when I was motocrossing it. Then I decided to thoroughly understand 2 strokes when I lived way up in the mountains and my 48cc motorized bicycle was too weak to handle the hills. www.dragonfly75.com/motorbike/

I am actually stunned that I got so much resistance to such a basic post about adjusting the idle screw. Maybe this forum name should be changed to Monkeys on Mopeds. When I put the same post on one of the most technical dirt bike forums the administrator, who knows tons about 2 strokes, gave it the thumbs up. Here I just get shit slung at me. better forum name: Shit Slinging Monkeys on Mopeds

from NAPA:

Cold air is denser than warm air, which means even a properly tuned carburetor may struggle with a too-lean mixture on a cold morning as it pulls in the same volume of air, but more tightly packed, increasing the air-to-fuel ratio.

Your carburetor needs to be adjusted according to the ambient temperature, humidity, and altitude of operation due to the oxygen density of the air changing with these variables.

https://www.fixyourdirtbike.com/fix/how-to/2-stroke-carb-tuning/

Cold air and hot air are different densities. The difference in air density from a California winter day to a summer day is approximately 5%, therefore your bike that was perfectly tuned for winter feels all sluggish on a hot day and your bike that runs crisply in summer will run lean in winter. Unless you adjust.

https://www.southbayriders.com/forums/threads/132589/

The pilot jet is not difficult to set. With proper air screw adjustment and a close initial setting from your engine tuner, fine-tuning should be painless. Once set the pilot jet is not terribly sensitive. You should only be required to adjust the setting when confronted with large weather changes or altitude swings of over 2000 ft.

http://www.maultechatv.com/techguides/carbtuning.php

https://www.hotrod.com/articles/hrdp-0406-density-altitude-tuning/

Re: About the Air Screw Adjustment

ha ha ha

whats the point of coming on here and posting nonsense that nobody cares about? you don't even own a moped.

unless you're just trying to drum up traffic for your site? makes no damn sense.

Re: About the Air Screw Adjustment

Michael Forrest /

Yeah you are right. I didnt realize this is a forum for turd slinging monkeys.

Its like trying to educate bacteria.

Re: About the Air Screw Adjustment

That was a fun read. Thanks guys. Now I'm gonna go out to my garage and turn all my screws indiscriminately.

Re: About the Air Screw Adjustment

shit slinging monkeys on mopeds indescrimanetly screwing

sounds about right!

Re: About the Air Screw Adjustment

Pics!

Re: About the Air Screw Adjustment

Dirty30 Dillon /

> Michael Forrest Wrote:

> -------------------------------------------------------

> Yeah you are right. I didnt realize this is a forum for turd slinging

> monkeys.

>

> Its like trying to educate bacteria.

So go away, your knowledge is generic and can be found anywhere. You want a pat on the back for regurgitating 2 stroke information? Good luck

Re: About the Air Screw Adjustment

I agree with this guy. Fuel is delivered to the engine by the carburetor, which is a very technical pumping mechanism with a miniature piston inside, this pistons travel is adjusted by the air screw that this guy wants you to keep adjusting for the mixture to be consistent through the entire rpm range. On the intake stroke of the two stroke engine the piston in the carb created a vortex of fuel that is forced by hydraulic induction through a jet. This jet is called the main jet and is aimed directly down the intake towards the spark plug. The jet must produce a lot of pressure in order to overcome the pressure differential which holds the engine ports open. If the jet of fuel is too low it will not spray onto the sparking plug and you need to adjust the angle of the jet to either "up jet" or "down jet".

There is also a choking mechanism on all carburetors which narrows the bore of the carburetor so the pressure differential between the compression stroke and the atmospheric pressure increases. This in turn makes the piston inside the carburetor move faster and pump more fuel through the jet at the spark plug. Excessive use of the choke will make the spark plug a darker colour because of the dark blue tint or dye in the oil that is mixed with the gasoline. This can be remedied by doing a plug chop, where you make the spark plug shorter by chopping off a section of the electrode which will expose some clean electrode.

On many engines there is a decompression or starter valve, these valves are placed in the engine on the exhause side of the combustion chamber. When you start the engine you need to open the decompressor valve. What that does is allows some of the stored up energy in the exhause pipe to go back into the combustion chamber. This energized exhause will ignite the first charge of fuel that enters the combustion chamber, starting the flame kernel which will light each subsequent power charge entering the chamber. Once the engine is running you close the valve, trapping the fire in the combustion chamber where it will continue to burn the fuel as it comes in. To shut off the engine you just need to open the valve, this will syphon off some of the flaming fuel into the exhause, where it will be stored up for the next time you need to start the engine.

Because there is a difference of 5% in temperature each day and 20% of humidity then the screw must be tightened all the way in and turned a full two turns plus the sum of the differential of the humidity and temperature as calculated on a standard humidex chart, first calculated into metric. So if the temperature is 80°F then it is 26.7°C and the humidity is 75% then the differential is 36°C, so recalculating the humidex factor back to standard where F = 1.8 * C + 32 we have is 97° so the screw needs a further 97° or 817° turned out from completely closed.

Re: About the Air Screw Adjustment

Bump for a padlock.

Re: About the Air Screw Adjustment

Tri-ped Dave O.D.B. /

Most of my mopeds have a Dellorto SHA. No air screw. No idle jet. So what do I do? Turn the entire moped when the humidity changes? I guess I am dumb as a bacteria. Maybe I should have returned my Nationl Merit Scholarship back to the taxpayers. along with my Phi Beta Kappa key back to the National Honor Society.

Re: About the Air Screw Adjustment

Tri-ped Dave O.D.B. /

After all this technical advice that is far beyond microbial comprehension, I wonder how my fleet runs so well and so fast without the air screw and without the idle jet? Must be some sort of mystical power or divine intervention.

Re: About the Air Screw Adjustment

Tri-ped Dave O.D.B. /

Rebel,

You forgot to calculate altitude as it relates to the proximity of the carburetor to the center of the mass of the Earth which as Einstein proved actually bends space. As you approach the center of mass, the gravitational pull increases exponentially, amplifying the venturi effect. Therefore you must regulate the aperture of the venturi accordingly.

Re: About the Air Screw Adjustment

Actually it is merely sorcery and alchemy...

> Tri-ped Dave Wrote:

> -------------------------------------------------------

> After all this technical advice that is far beyond microbial

> comprehension, I wonder how my fleet runs so well and so fast without

> the air screw and without the idle jet? Must be some sort of mystical

> power or divine intervention.

Re: About the Air Screw Adjustment

hahaha...

s u r e

If Earth was not flat that would be an issue... hahaha the things you say in jest...

> Tri-ped Dave Wrote:

> -------------------------------------------------------

> Rebel,

>

> You forgot to calculate altitude as it relates to the proximity of the

> he carburetor to the center of the mass of the Earth which as Einstein

> proved actually bends space. As you approach the center of mass, the

> gravitational pull increases exponentially, amplifying the venturi

> effect. Therefore you must regulate the aperture of the venturi

> accordingly.

Re: About the Air Screw Adjustment

Ok Michael we're all clear about the carb screws now. So can you explain port timing real quick? (edited)

Re: About the Air Screw Adjustment

I studied Indiscriminately Screwing OnMopeds at Shit Slinging Monkeys University, so I can give that a try if Michael is too bust perfecting his at least 10 motorcycles he has been tuning since 1973.

> live ɘvil Wrote:

> -------------------------------------------------------

> Ok Michael we're all clear about the carb screws now. So can you explain

> port timing real quick?

Re: About the Air Screw Adjustment

Probably Fred /

All my Air screws on my dellorto PHBG and PHVA carbs and mikuni tm24 carbs are around 1,5 turns out, I have the perfect four stroke sound and feel at 1/8th throttle,

and beat most stock 80-100 cc scooters to 50 mph!

Re: About the Air Screw Adjustment

Comrades....attention this is a code 22 zebra. Get on your blackbrrries and prepare to receive the launch codes. Ready when moped gurgles and is maximum horse power ( think Catherine the great comrade ) execute launch code 22 zebra 3x F . Go and bring glory to the revolution.

Re: About the Air Screw Adjustment

If you don't have an air screw, you need at least 6 different air filters. One for every season, plus two more for rain and fog (get extras for snow, humidity, elevation, etc.)

Then attach a small desk fan from Walmart with three adjustable settings.

In rainy weather, adjust your air flow by using a tool called a "garage."

If you find yourself riding a sea-level, snorkles are readily available. You'll need a hose adapter to reach your intake, but by inflating and deflating your lungs, you can adjust the air flow. Hence the term "naturally aspirated."

For a quick boost a pump from a fish tank can be attached.

Also, blowing into your gas tank will "oxygenize" your fuel, adding more air.

Re: About the Air Screw Adjustment

Tri-ped Dave O.D.B. /

Broken Arrow protocol. The launch codes have been compromized. All CNWTTY and higher go to DEFCON 1 assignments

boom.jpg

Re: About the Air Screw Adjustment

Rick Bergsma /

I adjusted my idle once , yep , once

Re: About the Air Screw Adjustment

> Rick Bergsma Wrote:

> -------------------------------------------------------

> I adjusted my idle once , yep , once

Same here . That was about 1 1/2 - 2 years ago and the bike has been ridden in altitudes from sea level to about 4,500 feet . That , in humidities from single figures to near 100 % .

Re: About the Air Screw Adjustment

...because we use the metric system...

> Rick Bergsma Wrote:

> -------------------------------------------------------

> I adjusted my idle once , yep , once

Re: About the Air Screw Adjustment

Comrades I need to bring to your attention in the in the Southwest horizon I saw a flaming object as if it was Helios on his chariot riding the sun to sunset It was Michael Forest he had perfectly adjusted his idle and his chariot usurped the power of the gods of Olympus bless the man

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