tuning the carburator

ben harpo

Member
I replaced the gaskets in my T0-30 carburator
because they were shot and leaking. I think I got
it back together correctly. Following the
instruction manual, I opened the main jet
counterclockwise 1 1/4 turn from the bottom.

I have very little experience with carburators,
but I have destroyed 2 stroke engines by running
them too lean. I obviously don't want to do that.

I'm told you can only tell if the mix is right
while under load. So while plowing should I open
the main jet in 1/16 turn increments until I see
black smoke and then close 1/16 until the black
smoke goes away?
 
well to get start I always begin with an idle. make sure the engine is slowed down to 400 rpm or lower to adjust the idle screw. keep in mind on the to30 carb running the idle screw in makes the mixture more rich were as on other carbs turning the screw in make the mixture more lean. as for the main jet it will pick up from the idle screw as soon as you give it throttle so at that point the idle screw will make no change if the engine is running to high rpm. back to main, from what I understand 1 1/4 turn is the most you what to turn the screw out, I believe mine is set somewhere between 7/8 and 1 1/4, but each tractor likes a little different setting. also it my help to use higher octane fuel as it is closer to what was available when the tractor was made
 
Makse sure that you don't lean to less than 1 full turn out. The engine is designed to have some charge cooling from evaporating the fuel in the mixture and going less than 1 full turn can give you some potential for burned valves.
 
The "idle air" or "idle needle" is the one you are referring to, not the idle screw. The idle screw is on the backside of the carb and adjusts the idle RPM, not the idle air/fuel mixture.
Engine must be completely warmed up to make proper adjustment. Once done, you should be able to quickly open the throttle from idle all the way to full RPM and it should increase in RPM quickly and without any coughing or spluttering. At full RPM you can adjust the high speed needle. Turn clockwise until it is too lean, you will be able to hear RPM drop or it start to sputter, you will also feel the exhaust manifold get very hot beside your hand! Don't keep it lean like that. Back it off from there. If you open it too far (too rich) you will hear the engine suffering and probably see some black exhaust (unburned fuel). Once you have it close, yes, put it under load and see if the governor kicks in and maintains the set RPM. If it coughs or splutters when the governor kicks in, open the high speed needle another 1/4 turn. Repeat until it is smooth under load. You may have to make small adjustments for temperature change. For me, I have to open it 1/4 to a 1/2 turn in the winter. Carb tuning is kind of an art. If you're not sure what you are listening for or looking for, best to ask someone to help you with it that's got some experience with it.

There is some good information over on the FENA website. Not sure if I'm allowed to post a link but Google Ferguson Enthusiasts of North America. Once on their site, click on the "resources" tab on the right.
 

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