How Much is Too Much

[manual]

I asked this Question but did not get a reply so I am going to try again.
How is your saw going to over speed if you have it set up for a 20" bar and then put a 16" bar on it. Why would it blow up. Yes I know that the carb should be adjusted. but how am I going to over speed it.

 

[JUDGE1162]

If the carb is set you should have not problem, however I have read that if you go too small you can have issues with over speeding the chain (too much stress on the chain) not sure if it is true but most chains do hae some sort of speed rating so I guess there is some issue with it.

 

[wagonwheeler]

My assumption was (assuming this was in fact true of course) that the chain drag/friction acts as a limiter and that if a saw max rpm is set for a given drag, reducing that drag can allow max rpm to be exceeded.

Chaser

 

[fishhuntcutwood]

From your original question, my reply-

You can reduce the load enough to raise the RPM's sufficiently to cook the saw, without adjusting the carb. That's why Andy says technique is so important. The saw's performance and hp output are the same, but the load is less, so it'll run faster and you need to know to not run it too fast. Running too fast is bad, as you know.

There you have it-

My assumption was (assuming this was in fact true of course) that the chain drag/friction acts as a limiter and that if a saw max rpm is set for a given drag, reducing that drag can allow max rpm to be exceeded.

Chaser

If your saw is running 14,000 RPM WOT, lets say it runs 9,000/10,000 whatever in the cut with a 28" bar. That's with the load of that 28" bar. Put a 16" bar on that, and don't slow the saw down via carb adjustment, and you could be running 12,000 or 13,000 sustained, in the cut. Now, I'm just guessing at these exact numbers, but it's what would happen. It's all about the load of the chain. That's why you tune your saw with bar and chain installed. Your saw would friggin scream with no chain on there, and then when you put one on to cut, your adjustment would be inaccurate. Same thing if you tune it with a 28" or 32" and then put on a 16" bar and chain. Your saw would be tuned for the higher load of the longer chain.

 

[AlexP]

Follow up question

I have a question which relates to how the RPM adjustment is made if the saw is overspeeding. Do you adjust the high speed mixture screw to slow the saw down at WOT or is the adjustment made in the throttle linkage or both places or where?

I have been wondering about this very issue and I hope Manual doesn't mind my piggybacking on this thread. Thanks.

Alex

 

[Lakeside53]

You adjust the mixture screw richer to slow the engine down, but...

Don't chase the theoretical WOT with a LONG bar - you can set the saw too lean. The WOT adjustment is just one method of getting an approximate mixture setting.

Set it with a bar typical for the saw, and forget it if going longer. The only reason to check it on shorter bars is to make sure your RPM hasn't exceeded the max allowed, but, this is an operator controllable issue and much of this is a waste of time worrying about. If the operator is screaming the saw in the cut, then he should be slapped. If the mixture is set about right - slightly rich of peak, (there is only one "perfect" mixture for given atmospherics... and it has nothing to do with bar length) the operator easily controls the WOT setting....

 

[wagonwheeler]

Is it just me or does anyone else hear Charlton Hestons 'Moses' voice when Lake explains things...

All I can say is "Yes sir! I will try to do better!"

Chaser

 

[manual]

Thanks guys but bare with me.
Now I have modded the muffler. and that puts a gain on rpm.
Thats the whole Ideal for the mod to gain rpm.
if the saw is rated at 14,500 why would it blow up in the cut a 13,000

 

[manual]

I have a question which relates to how the RPM adjustment is made if the saw is overspeeding. Do you adjust the high speed mixture screw to slow the saw down at WOT or is the adjustment made in the throttle linkage or both places or where?

I have been wondering about this very issue and I hope Manual doesn't mind my piggybacking on this thread. Thanks.

Alex

Naw go for it, This is how we learn

 

[Lakeside53]

Thanks guys but bare with me.
Now I have modded the muffler. and that puts a gain on rpm.
Thats the whole Ideal for the mod to gain rpm.
if the saw is rated at 14,500 why would it blow up in the cut a 13,000

14.500 is a MAX rating for a few seconds, not a continuous rating. It's to stop things coming unglued. Your cutting speed is probably 9-11k optimally. Your car has a redline of say 7K (insert truth here if incorrect), but that doesn't mean you can hold it there while driving.

Assuming you're are not racing or you give a damn about saw life, the idea of a mod (your muffler mod anyhow ) is not to gain rpm, but to gain power, cooling or both. After your mod you readjusted the mixture and the saw should still not "run" (WOT) at more than 14,500. In the cut the saw speed varies dramatically depending on the wood size... You still have to control the rpm by application of appropriate pressure or whatever.

If you are cutting at 13k, get a bigger sprocket, or bigger wood, or smaller saw.

Just duct tape a tach to the back of your air cleaner and watch it (not to attentively!) while cutting..

 

[Lakeside53]

Is it just me or does anyone else hear Charlton Hestons 'Moses' voice when Lake explains things...

All I can say is "Yes sir! I will try to do better!"

Chaser

I hear it all the time!!! I used to be Schizophrenic, but we're getting better...

...but, if you've heard my accent, well... let's just say Charlie and me are worlds apart.

 

[Kneejerk Bombas]

Really, your saw won't run it's fastest set at factory no load maximum RPM. It'll cut faster when set a bit lower.
The only way to figure out the optimal RPM is to set up a log and do timed cuts.

 

[retoocs555]

If the carb is set you should have not problem, however I have read that if you go too small you can have issues with over speeding the chain (too much stress on the chain) not sure if it is true but most chains do hae some sort of speed rating so I guess there is some issue with it.

A chain speed rating??? Is that info out there?

I've never seen it published.

 

[Dan Forsh]

I hear it all the time!!! I used to be Schizophrenic, but we're getting better...

...but, if you've heard my accent, well... let's just say Charlie and me are worlds apart.

Lake are you J,A,F,A?

Dan

 

[fishhuntcutwood]

...but, if you've heard my accent, well... let's just say Charlie and me are worlds apart.

I've met you, and I don't hear Moses, I just hear you talking, and then think about how stupid I am.

I can't even outsmart you talking about aircraft or birdwatching. You know those too!

 

[manual]

14.500 is a MAX rating for a few seconds, not a continuous rating. It's to stop things coming unglued. Your cutting speed is probably 9-11k optimally. Your car has a redline of say 7K (insert truth here if incorrect), but that doesn't mean you can hold it there while driving.

Assuming you're are not racing or you give a damn about saw life, the idea of a mod (your muffler mod anyhow ) is not to gain rpm, but to gain power, cooling or both. After your mod you readjusted the mixture and the saw should still not "run" (WOT) at more than 14,500. In the cut the saw speed varies dramatically depending on the wood size... You still have to control the rpm by application of appropriate pressure or whatever.

If you are cutting at 13k, get a bigger sprocket, or bigger wood, or smaller saw.

Just duct tape a tach to the back of your air cleaner and watch it (not to attentively!) while cutting..

Thanks I am drawing a picture in my mind. Load/ no Load.
So in 2 cycle engines power gains don't always follow rpm gains ?

 

[Lakeside53]

Thanks I am drawing a picture in my mind. Load/ no Load.
So in 2 cycle engines power gains don't always follow rpm gains ?

You have to "develop" power by loading the engine.

 

[Lakeside53]

Lake are you J,A,F,A?

Dan

O.k., you've got me... some local idiom? I left England when I was 7, didn't get back until I was 25... Must have missed something...

 

[manual]

J.A. F.O. is just another f_ _ _ ing observer
Don't know what J.A.F.A. is...Hmmmmm

 

[Dan Forsh]

No... okay, wide of the mark I guess. :blush:

Manual was almost there. I thought you were originally a New Zealander?

Jafa is a term of "endearment" used by other Kiwi's for those from Auckland.