How long can you keep the throttle wide open without load?

[anynameyouwish]

Question for you all (couldn't find the answer online): How long can you keep the throttle at full when tuning the H jet? My tach (proline solo) takes a few seconds, sometimes 3-5, to register the RPM reading. Is it OK to run WOT without load for, say, 5 seconds? What I've been doing is full throttle for few seconds, note RPM reading, wait for a few minutes, adjust carb by an eighth turn, recheck RPM, etc.

(Thank you all for excellent advice on the other threads I've started recently!)

 

[Jza]

I've done the same . Warm saw up , check rpm. Let it idle for a few seconds , check rpm . Dont think about it too much . Running a blunt chain forcing it into the wood is alot worse lol

 

[HansFranz]

I started out using a tach for tuning...now I never use it anymore and instead listen for the "4-stroking burble/flutter"...for me, that tells me everything I want to know. As long as I'm getting that blubber sound at WOT under no load (you will also often see some smoke from unburned gasoline when it's running like this), I figure it's not going too fast, and if the sound "cleans up" under load in the cut (at which point the sound will change and the smoke disappear), and the saw pulls well, I figure it's going fast enough. Whatever the case, you're safer running "too rich" than "too lean."

That seems to be the same method the tech at my Stihl dealer uses.

It only takes about a second of WOT no-load operation to confirm that it's making that sound...and in a long session of cutting, I will generally check this a few times to make sure that it's still rich enough (I believe a hot saw will tend to "lean out" the mix...)

There are some .wav sound files on "saw tuning" page at the Madsen chainsaw site that will let you hear what you're looking for.

 

[user 122190]

Going to the way way back machine. Once upon a time the folks here use to tune their saws several times a day, in the cut even. I had to learn how to tune my ms290 because it needed a carb cleaning and rebuild. I was avoiding the rebuild, but the tuning accomplished less and less each and every time til finally I took carb off and gave it the full treatment.

Regarding tuning goes, you hardly ever have to bother, unless that something you enjoy doing.

 

[Mad Professor]

Until it seizes or a bearing explodes.
I tune by ear

 

[anynameyouwish]

Found something interesting that I thought I'd share. My 395xp manual has basically no instructions for tuning the carb - the manual is "tuned" to saws that have carb limiters. But I managed to find a version of the manual which has a section "Carburettor without movement limiters". And that section says

The high speed jet H influences the power and engine
speed of the machine. If the high speed jet is set too
lean (H-jet screwed in too far) the machine will over-
rev and this will damage the engine. Run the machine
at full throttle for about 10 seconds. Then turn the H-
jet 1/4 turn anti-clockwise. Run the machine at full
throttle for another 10 seconds or so and listen to the
difference in the fast idle speed. Repeat this
procedure with the H-jet turned a further 1/4 turn anti-
clockwise.

I've bolded the bits which assures me that running the saw at full throttle for 10 seconds is OK. So, my question is answered: 3-5 second is no big deal.

The difference between the manuals is, as you might expect, that my original one was US, the one I quoted above is EU.

 

[NSEric]

If it's four stoking at full throttle no load holding it there for a bit wont hurt anything.
If it's lean and screaming it'll blow up after a bit.

I too stopped using my tach and set them so the four stroking just stops when cutting.
For milling set it so rich it doesnt stop four stroking until you push on it in the cut.

 

[anynameyouwish]

If it's four stoking at full throttle no load holding it there for a bit wont hurt anything.
If it's lean and screaming it'll blow up after a bit.

I too stopped using my tach and set them so the four stroking just stops when cutting.
For milling set it so rich it doesnt stop four stroking until you push on it in the cut.

Someday I'll be confident enough to tune by ear. Until then my tach is a very useful crutch..

 

[Okie]

Someday I'll be confident enough to tune by ear. Until then my tach is a very useful crutch..

You might consider just the opposite. 9just so you can say to your self you used your tack

Set the H purposely rich by ear then use your tach.

I have a high dollar tack that works great, BUT I have not used it in couple of years on a chainsaw, except on 4 cycle small engines to set the idle and governor.

I do as mentioned above set the H jet rich and then test in a cut. Usually see little smoke at no load when just into the CCW rich H jet setting.
I've seen chainsaws lock up into a full bar cut under heavy load due to running lean.
They would be ok doing small fast cuts on/off the throttle but a 1 minute or longer heavy full bar load would overheat and score the piston.
I've found that using a IR thermometer to confirm that a saw IS NOT overheating (getting a severe fever) in the cut is more reliable than tuning using a tach.

 

[rogue60]

I've got two stroke mowers 125cc to 170cc and I use them year round they run great every time I use them. I've never tuned them ya can't is no adjustments for tuning on the carbs lol

 

[bwalker]

I've got two stroke mowers 125cc to 170cc and I use them year round they run great every time I use them. I've never tuned them ya can't is no adjustments for tuning on the carbs lol

Many two-stroke in the past were set so rich it didnt matter.
Outboard motors are one example. Never set the carb in one and have ran them from 100 degrees down to the teens.

 

[holeycow]

What's a tach?

 

[bwalker]

Someday I'll be confident enough to tune by ear. Until then my tach is a very useful crutch..

Tuning by ear is a crap shoot and often results in a overly rich tune.

 

[bwalker]

Question for you all (couldn't find the answer online): How long can you keep the throttle at full when tuning the H jet? My tach (proline solo) takes a few seconds, sometimes 3-5, to register the RPM reading. Is it OK to run WOT without load for, say, 5 seconds? What I've been doing is full throttle for few seconds, note RPM reading, wait for a few minutes, adjust carb by an eighth turn, recheck RPM, etc.

(Thank you all for excellent advice on the other threads I've started recently!)

You can run a chainsaw full throttle no load for a long time without issue.
The reset procedure for Mtronic saws takes 30 seconds I believe.

 

[anynameyouwish]

Saw has been tuned to 12K, which is just where it stopped 4-stroking in the cut; at 11.8K I could hear it slightly blubbering under load. After doing this, I can't believe I was milling with the carb limiters on.

This is fun stuff! Thanks everyone!

 

[Hulpio]

I do just tune it leaner until it stops 4 stroking then back a bit. Every now and then check if light 4 stroking is still there.

 

[ZeroJunk]

If I tune by ear I will always be way rich.
I suspect the majority of guys that tune by ear will likely be richer than what they would come up with using a tach. Not bad thing I wouldn't think necessarily.

Anyhow, I work on a lot of stuff. These saws that are ruined because they are tuned too lean or not enough oil in the mix seem to elude me.

Don't see the point in holding one wide open any longer than it takes to stabilize , 2 or 3 seconds.

 

[slowcar281]

Holding a saw at WOT for 5 seconds with no load won’t hurt a thing. Unless you are so lean that it’s turning 16k.

I’ve found a tach to be really helpful when tuning a strato saw with a limited coil, so you can see exactly where the rpm’s are. Sometimes it’s hard to distinguish hitting the limiter vs 4 stroking on certain saws using your ears alone.

 

[rogue60]

Many two-stroke in the past were set so rich it didnt matter.
Outboard motors are one example. Never set the carb in one and have ran them from 100 degrees down to the teens.

My 2T mowers all have governors as well. Accept one it's a rotary valve 2T with no governor you control revs with the throttle...WOT it scares me lol

 

[Doorfx]

What's a tach?

An apprentice tech.