STIHL hedgetrimmer HS82 T and R : carburator "H" screw setting???

[rhkraft]

I have been working on 2 -cycle engines since they came out in yard tools. The factory L, H, and LA settings, i.e. screw turns from closed are a beginning point to get your engine running and keep it running. Adjust the idle (L) screw first. If the engine dies, adjust the LA (idle speed) until the engine will run without stalling. Then adjust the L screw until it runs smoothly. Turn the LA in until the engine runs at a desirable idle speed. If the idle is not smooth, adjust L a little until it is smooth. If the idle speed is correct and the engine idles well, all the powered machinery will be stopped. That is stopped, no creep or movement. The machine is safe. Now open the throttle to full power. The factory setting will maintain the right rpm. Only adjust the H screw if the engine is not smooth. If the engine is rich, it will run rough and may smoke - turn the H in. If the engine is running too lean it will stumble and may stop when the throttle is opened quickly. Adjust for smooth operation. Remember the factory settings are a place to start. Air density due to altitude does require re-adjustment.

Item 2. If the engine runs well at first but gets worse over time when you use it next time and needs to be re-adjusted, check this first. If the engine runs well when the tank is full, check the tank when the roughness starts. If the fuel level is down, the problem may be a cracked fuel line in the tank. The fuel pump will suck fuel through the crack when the tanks is full, but when the fuel level goes down and the crack is exposed to the air, the fuel pump will suck in some air and the engine will run rough. Changing the fuel line is an easy fix. Good Luck

 

[Tiger Small Engine]

I have been working on 2 -cycle engines since they came out in yard tools. The factory L, H, and LA settings, i.e. screw turns from closed are a beginning point to get your engine running and keep it running. Adjust the idle (L) screw first. If the engine dies, adjust the LA (idle speed) until the engine will run without stalling. Then adjust the L screw until it runs smoothly. Turn the LA in until the engine runs at a desirable idle speed. If the idle is not smooth, adjust L a little until it is smooth. If the idle speed is correct and the engine idles well, all the powered machinery will be stopped. That is stopped, no creep or movement. The machine is safe. Now open the throttle to full power. The factory setting will maintain the right rpm. Only adjust the H screw if the engine is not smooth. If the engine is rich, it will run rough and may smoke - turn the H in. If the engine is running too lean it will stumble and may stop when the throttle is opened quickly. Adjust for smooth operation. Remember the factory settings are a place to start. Air density due to altitude does require re-adjustment.

Item 2. If the engine runs well at first but gets worse over time when you use it next time and needs to be re-adjusted, check this first. If the engine runs well when the tank is full, check the tank when the roughness starts. If the fuel level is down, the problem may be a cracked fuel line in the tank. The fuel pump will suck fuel through the crack when the tanks is full, but when the fuel level goes down and the crack is exposed to the air, the fuel pump will suck in some air and the engine will run rough. Changing the fuel line is an easy fix. Good Luck

I am glad there are so many proficient handheld engine tuners out there. More than one way to skin a cat.

 

[TobyU]

I am glad there are so many proficient handheld engine tuners out there. More than one way to skin a cat.

Yes, and more often than not, better ways than what the factory service manual shows.
This is often the case where the service manuals show you the basic way to do it which will get the job done or close enough to perfection or maybe even perfection but people who do it all the time typically fine better more efficient ways to get to that same point.

 

[bertsmobile1]

I have been tuning carbs since I was 12 and always do as rhkraft
Start with the idle ( L ) jet then the throttle stop then the main jet
OR in my case as they were mostly Amal carbs on motorcycles
Pilot air then slide cut away then needle jet then main jet
Golden rule in all things mechanical only adjust one thing at a time
Since buying the repair run I have tried the "factory" methods that seem to be getting more & more complicated on a daily basis and as far as I can see they are plain BS.
I will assume that EPA regulation compliance comes into play so at no time in the tuning sequence the engine cam be allowed to run rich for fear of the pollution extinguishing all life on the planet in a single day
With the exception of rotary valve carbs the idle jet supplies fuel 100% of the time so if it is not right then nothing else can be right
So you start there
For 60 years it has always been lean till the engine faulters, rich to the engine faulters then just a touch on the rich side of the mid point between the 2 extremes
With some of the fast reving 2 strokes I alter this slightly to rich till it 4 strokes then slowly lean off till upper RPM limit has been achieved as when doing 10,000+ rpm slightly too lean can damage the engine very quickly
Naturally it takes a bit of ear memory to be able to identify the very first sounds of running too lean and of course the leaning off has to be done VERY SLOWLY because on 2 strokes fuel can condense in the crank case so what seems to be right can actually become way too lean when this condensed fuel burns off

 

[Hammermechanicman]

IF your ear is that good then you should be read CW at 20+ words per minute. Here I was only get about 15 words to pass my General Class license test.Even they wanted to see written copy which I could keep up with the conversion.

You would have enjoyed the Army's Basic Morse school at Ft. Devens MA. You had to be able to copy 18WPM in 12 weeks. You got to copy code for 8 hours a day. Flunking out got you sent to cook school or infantry. When I got out of Uncle Sam's employment I could do 25. But that was about a half century ago.

 

[Flatsix]

I am very happy with all your advise and documentation that you have sent in this thread. I still did not tune my famous HS82R - the only reason is that till now I have postponed the action because I am "affraid" to do it.

The adjusting of the LA and the L screw do not make me nervous : I am able to tune so that I have a good respons on the gas and at the same time I have a good idling. (I do turn L out till it runs very bad - then I do the opposit buy turning L-screw in till again it almost stalls. Then I take the middle (sweet) spot between these two positions. Then I turn slowly out till the point where it is low in rpm and just before it beginns to turn less smooth. That is the point where I set it, just before it beginns to run rougher)

I will do the "factory" setting with the procedure of 3300 rpm and then drop the rpm to 2800rpm with the L-screw, and see where it gets me. I will let you know my findings when I have done it...

But the setting of that "H"-screw is where I am affraid of, because I have never done it - so no experience with my ear - and not possible to depend on my rpm-meter as on the HS82 you find that rpm-limiter that kicks in.

I know that when turning out (richer) the burble/4-stroke sound comes - at the other side when turning IN (leaner) the high-sound of too lean comes. I have slowly turn out from the high lean-sound till the burble/4-stroke is there. Then turn slightly back IN till burble/4-stroke is gone. That is the point to set it?? Am I right?

When you are turning IN till burble goes away - do you set it so that there is still a slight burble/4-stroke - or do you turn till really all the burble is completely gone???

 

[bertsmobile1]

OK
you need a resonable tacho
When you set the L and LA (throttle stop ) close the H fully so you are only running on the L jet as the engine was intended
Open the H jet engine running
If the engine speed picks up then the LA is out too far
Once you have your idle happy then open the H needle about 2 full turns Do a quick acceleration and the engine should 4 stroke ( miss rich )
If this happens then tighten the H watching the tach till you get to the prescribed maximum rpm
The high speed cut out is usually 10% higher than max RPM

 

[TobyU]

I am very happy with all your advise and documentation that you have sent in this thread. I still did not tune my famous HS82R - the only reason is that till now I have postponed the action because I am "affraid" to do it.

The adjusting of the LA and the L screw do not make me nervous : I am able to tune so that I have a good respons on the gas and at the same time I have a good idling. (I do turn L out till it runs very bad - then I do the opposit buy turning L-screw in till again it almost stalls. Then I take the middle (sweet) spot between these two positions. Then I turn slowly out till the point where it is low in rpm and just before it beginns to turn less smooth. That is the point where I set it, just before it beginns to run rougher)

I will do the "factory" setting with the procedure of 3300 rpm and then drop the rpm to 2800rpm with the L-screw, and see where it gets me. I will let you know my findings when I have done it...

But the setting of that "H"-screw is where I am affraid of, because I have never done it - so no experience with my ear - and not possible to depend on my rpm-meter as on the HS82 you find that rpm-limiter that kicks in.

I know that when turning out (richer) the burble/4-stroke sound comes - at the other side when turning IN (leaner) the high-sound of too lean comes. I have slowly turn out from the high lean-sound till the burble/4-stroke is there. Then turn slightly back IN till burble/4-stroke is gone. That is the point to set it?? Am I right?

When you are turning IN till burble goes away - do you set it so that there is still a slight burble/4-stroke - or do you turn till really all the burble is completely gone???

That style of a procedure is always worked nicely for me.
I have never used a tach for a two-stroke machine.
You also have to make sure if it's a string trimmer that you have the line out to the full length right to where the cutters will cut it off so you're getting proper RPM and proper resistance when you torque the engine up and rev it up from an idle otherwise your adjustments will be off.
With a string trimmer I find I like to get it to where the burble goes completely away and it smooths out and maybe even a little bit more but we're talking just to smidge nothing like a quarter or even 1/8 of a turn or maybe pushing 1/8 maximum because I don't want it to dip back down into the too rich when it's running.
However with a chainsaw it is often the best overall approach to have them a little bit rich when they're running with no load on them because then when you put the chain into actual wood it will need a little bit more gas and it will be at that perfect spot to where it's not rich and will be running it's best without being on the lean side.

 

[Joed756]

I'm confused by 2.5 and 2.1/8", I read 2.5 as 2-1/2 rotations but I don't know what you mean by 2.1/8".

 

[TobyU]

I'm confused by 2.5 and 2.1/8", I read 2.5 as 2-1/2 rotations but I don't know what you mean by 2.1/8".

You have .5 turns - or 1/2 .
.25 or 1/4. Then half of that which would be 1/8 also 45°