I bought this aftermarket carb from ebay years ago(China) but I have some questions about it. Is the valve on the throttle side suppose to close all the way? It has this plastic idle screw that stops it from doing so and I can only screw it back so far due to the brass screw right below it. Also I think this brass screw next to the idle plate is to adjust the fuel ratio not sure though. Not sure what the brass screw is directly below the plastic screw for either.
Can anyone give me some insight on this carb and maybe how to adjust properly so there is no issues. My current problem is high revving/idle but I replaced the governor spring and breather tube which was torn. Also I need new gaskets for this carb which I am waiting on. I just don't know how to adjust this carb.
Also I am not saying there is anything wrong with this carb or that the problem I am having is directly related to it, I just want to learn more about it if I do need to do some adjustments.
No the throttle valve can not close all the way or no fuel & air will get into the engine.
That is why the plastic stop screw is there.
The idle mixture screw allows a fuel rich air stream to bypass the throttle valve at idle.
In = leaner
Out = richer
You adjust it by holding the throttle against the stop so it can not move, because the governor will try to make it move as the engine speed changes.
You then turn that screw in & out very slowly till the engine falters rich & lean.
The proper place is 1/2 way between the place where it faltered rich & faltered lean.
For safety err slightly on the rich side.
If the idle is too high screw the plastic screw out allowing the throttle to close further.
You may have to readjust the idle mixture screw.
Continue till you reach your target revs ~ 1500.
Make sure that there are no air leaks before you start by saturating the joints with WD 40 or similar from a trigger pack, not a spray can.
The engine speed should not change if all is good.
Thank you for the reply and wealth of knowledge. I'm sorry but which one is the idle mixture screw? The one below the plastic stop screw or the one on the side of the carb? Also do I adjust this while the mower is running and at what throttle position or does it need to be off?
The one in the little hole to make it hard for you to play with.
Under the plastic screw is the idle jet which controls how much fuel is mixed into the air / fuel mix that enters through the idle port where the screw is
So the big plastic is a idle stop screw. The one on the right is the idle mixture screw and the one below the plastic screw is the idle jet? Do I have that right? Does the idle jet get adjusted often or just leave it completely seated?
You got it.
The one under the plastic screw is fixed
You only need to adjust the one on the right if you removed it.
Like all jets the initial setting will be x number of turns from lightly seated.
If you did not do screw it in first to work out what x was then good luck.
ALL CARB ADJUSTMENTS MUST BE DONE ENGINE RUNNING>
How the hell can you hear, see, feel the engine faultering if it is turned off ?
Thanks! I did I was just making sure. I am waiting on gaskets from Amazon. So as soon as I get those in and sandwich everything together I will let you know how it all works out. Thanks for the advice!
Is it possible to do the adjustments while the engine is off? There is no way I have access to those screws without taking the some pieces off. I got all the gaskets on and still runs like it's going to blow up.
Nope.
You will need to make some spacers to hold the carb tight against the engine.
If you start the engine and it immediatly races away uncontrolled then either the governor is broken / not adjusted or conneced wrong.
The governor ALWAYS TRIES TO CLOSE THE THROTTLE, not open it.
people always seem to get this backwards in their mind.
The throttle lever tries to open the throttle & the governor tries to close it.
The two are balanced by the spring connecting them together.
Okay I will see what I can do. From what I can tell when adjusting the throttle the govenor is not moving to much which is not moving the arm and spring to the carb.
There are a million U-Tube videos about how to adjust the governor and some of the better ones will show you how to test the governor.
A lot easier to watch than explain.
#12
tom3
Pretty sure that's the first time I've seen a metering jet (just under the idle speed adjust) open to outside air on a carb.
Okay I was able to get the rpms down via the plastic idle screw. However the rpms stay the same regardless of speed fast or slow. The only exception is when the blades are engaged I am able to change the speed. The governor arm doesn't move much until I turn it to off. I have a new governor spring installed and confirmed that the governor rod and spring is installed correctly. The rest of the springs seem to be doing their job.Does that make since to you?
