NT Carb.... No air adjustment

[Gh0stRider]

Do the Gh0stRider aquarium pump mod!

an intake leak would cause the engine to run lean, even if it was made by using an adjustable screw of some sort. A mixture screw does just what it's called...it allows you to adjust the air/FUEL mixture at the carb. an adjustable screw in the intake would only allow you to adjust the air and it will always run too lean if it is sucking extra air anywhere after the carb.
you will always get more power / shorter piston life out of an engine that is running too lean.

There are no air/fuel adjustment screws on carburetors.

Either it is an air adjustment screw, or a fuel adjustment screw. Air adjustment screws are generally on the air cleaner side of the carburetor, and fuel adjustment screws are generally on the engine side of the carburetor.

I have personally done the modification to my generic chinese engine as it was running too rich at idle and loading up the engine with fuel. Moving the needle lower would fix the idle but cause an overly lean condition at mid throttle. Adding the air bleed worked well, but you have to go back and forth on the idle speed and air bleed screws to get it balanced perfectly.

Go to a pet store and buy an air regulator valve and an inline air filter and hook it up to the intake tube with a brass barb obtained at a hardware store. Drill and tap a hole in the intake tube and screw in the brass barb. (I sealed mine with high temp PC7 epoxy)

 

[danlandberg]

SORRY MP; Did not mean to waist any of your time! But I'm thought it MIGHT work. I just wanted an opinion!

 

[Gh0stRider]

Read one post above - it does work, I've done it.

 

[motorpsycho]

There are no air/fuel adjustment screws on carburetors.

Either it is an air adjustment screw, or a fuel adjustment screw. Air adjustment screws are generally on the air cleaner side of the carburetor, and fuel adjustment screws are generally on the engine side of the carburetor.

I have personally done the modification to my generic chinese engine as it was running too rich at idle and loading up the engine with fuel. Moving the needle lower would fix the idle but cause an overly lean condition at mid throttle. Adding the air bleed worked well, but you have to go back and forth on the idle speed and air bleed screws to get it balanced perfectly.

Go to a pet store and buy an air regulator valve and an inline air filter and hook it up to the intake tube with a brass barb obtained at a hardware store. Drill and tap a hole in the intake tube and screw in the brass barb. (I sealed mine with high temp PC7 epoxy)

sorry but you are wrong.
There are air /fuel mixture screws on carbs (maybe not these little 2 stroke carbs).
opening the screws allows more air in, closing the screws allows less air in.
actually what you are adjusting the the air that mixes with the amount of fuel that your jet is flowing, so technically yes...they are air/fuel mixture screws even tho you are not actually adjusting the amount of fuel.
so you aree saying that a leak at the intake manifold is good with your pet store filter idea? wow!!!!
if it's runnning too rich after adjusting the needle jet, the only RIGHT way to lean it out is by changing the jet to a smaller size.
go drill a hole in the intake manifold of your car and tell me how well it runs.

 

[Gh0stRider]

sorry but you are wrong.
There are air /fuel mixture screws on carbs (maybe not these little 2 stroke carbs).
opening the screws allows more air in, closing the screws allows less air in.
actually what you are adjusting the the air that mixes with the amount of fuel that your jet is flowing, so technically yes...they are air/fuel mixture screws even tho you are not actually adjusting the amount of fuel.

So I'm wrong, but then you prove that I am right?

What I did was to install an external air bleed screw on my carb. It does the exact same thing an internal air bleed screw does. The amount of air introduced into the intake is very small and will only affect idle mixture. This is how an idle air bleed works on cabs with internal air bleeds. Opening the throttle does not close off the idle air bleed adjustment, it still continues to introduce air at all throttle positions - it is just so little air that it has a negligible effect on the mid and high speed circuits.

Go ahead and make fun of the setup, but I know that a good aquarium pump air regulator valve has O-ring seals and can precisely adjust the amount of air introduced. Adding the inline filter solves the problem of drawing unfiltered air too.

Go for it Dan, you won't be disappointed.

 

[danlandberg]

There was not a TON of air getting in, It was only a 1/4 oz or so. LOL.

 

[motorpsycho]

there's nothing wrong with a good old fashioned debate....i do not look at this as an argument.
each of us has our opinion on the subject...neither of us is right or wrong i guess.
If you say it works, then it works.
In my opinion, i wouldnt do it...i can not prove to you that you are right or wrong.
and i can not prove that i am right or wrong.
i'm just going by experiences that i've had, and my mechanical knowledge.
No, i was not mnaking fun of your pet store idea. actually, i love it when people think of alternative ways of making parts.

 

[Gh0stRider]

there's nothing wrong with a good old fashioned debate....i do not look at this as an argument.
each of us has our opinion on the subject...neither of us is right or wrong i guess.
If you say it works, then it works.
In my opinion, i wouldnt do it...i can not prove to you that you are right or wrong.
and i can not prove that i am right or wrong.
i'm just going by experiences that i've had, and my mechanical knowledge.
No, i was not mnaking fun of your pet store idea. actually, i love it when people think of alternative ways of making parts.

Give it a try then! You won't be disappointed.

Every carburetor that has an air bleed screw for idle mixture has an "introduced vacuum leak" - but the key is that it is a controlled vacuum leak, not one introduced by a bad gasket or a hole drilled in an intake. These air pump valves can be adjusted so the air introduced is a infinitesimal amount. Just enough needed to get things running crisply.

These ultra simple generic Chinese engine carbs do not have any adjustment for idle mixture, they don't have a dedicated mid range circuit other than the jet needle in the needle jet and a main jet that seems to be lean for EPA considerations.

My fix was to keep the jet needle high enough to allow for a good mid range (no lean bogging) but the idle mixture was too rich - so I corrected that by introducing a controlled amount of air through the aquarium valve and balanced the throttle stop and air bleed to provide a nice smooth idle. The setup is like a motorcycle carb where you must go back and forth to balance idle speed and a/f mixture with the two adjustments.

These simple carbs do a good job out of the box, but can be made much better with some simple, common sense modifications.

 

[danlandberg]

I understand MP; No argument, it's just a discussion and learning curve! I also have over 20 years technical experience (all hands on). I just had a thought, and wanted some other input! I did not get mad about anything. But I did think about sending you a link that is funny. Just don't know how to yet.

 

[AussieSteve]

Go for it Dan, you won't be disappointed.

Not good advice. Besides other considerations, GhostRider, you set out to cure a lean mid-range condition, not a rich one, which is Dan's problem.
Also, as you say, you only affected idle mixture with your mod - that's not what Dan wants, although in reality it will slightly affect the mixture at all throttle openings, of course.
Dan wants heaps of air, so that it noticeably affects the mid throttle range.
Your trick worked for you at idle, but with enough of a leak to do what Dan wants, there's the potential to cook the top end.

a main jet that seems to be lean for EPA considerations.

In reality, the majority of people find that the jetting is too rich standard and have to go down in main jet size. In my case, an 0.79mm jet was stock but I needed to go down to 0.72mm before the WOT mixture was right.