Chainsaw Repair

Husqvarna - Stihl - Poulan - Jonsered - Dolmar chainsaws and more => Husqvarna => Topic started by: 05_sprcrw on April 06, 2011, 08:31:33 am

Title: Tuning a saw
Post by: 05_sprcrw on April 06, 2011, 08:31:33 am
I have a Husqvarna 394xp that I am going to tune properly (right now I just have it rich, it is always 4 stroking) I purchased my tach so I can set it by the numbers. I was wondering if it makes a difference on how fast the motor is turning with the size of the bar and chain on it.

For instance I cut with a 20" bar on the 394 90% of the time but will throw a 28" bar on from time to time. My initial thinking is that I would want to tune the saw with the smaller lighter chain on so that I don't over rev it by tuning the saw with a heavier chain on and then put the smaller lighter chain on. Is this true or will the engine run the same rpm with both chains (not under a load, so just for tuning purposes).
Title: Re: Tuning a saw
Post by: HolmenTree on April 06, 2011, 09:23:34 am
It won't make alot of difference from 20" to 28". But the powerband on the 394 will be a little different. At WOT rpm will be the same, but with the 20" b/c installed from idle to WOT the saw will respond quicker, being more "snappy".
Set your rpm at WOT for  what is called for.

Willard.
Title: Re: Tuning a saw
Post by: 05_sprcrw on April 06, 2011, 09:33:36 am
Thanks I figured I was over thinking it but wanted to make sure. I figure I did everything else right on the rebuild (first one) and I didn't want to make some simple error and ruin it because I didn't ask.
Title: Re: Tuning a saw
Post by: Cut4fun . on April 06, 2011, 01:11:54 pm
Here is Madsen's carb tuning with wave file to listen to.

http://www.madsens1.com/saw_carb_tune.htm
Title: Re: Tuning a saw
Post by: 05_sprcrw on April 07, 2011, 08:41:15 am
I have read the Madsens guide it definitely does a good job explaining how to tune a carb. I however don't trust my ears enough to do it this way. I have a tachometer coming to tune the saws to the rpms recommended by Husqvarna.   
Title: Re: Tuning a saw
Post by: wannab12 on April 07, 2011, 08:55:22 am
Is it a stock rebuild ? ported ? muff mod. only ? I think these will come into play as well. JMHO.

Steve
Title: Re: Tuning a saw
Post by: mdavlee . on April 07, 2011, 02:37:06 pm
Try tuning the chainsaw by ear. Then put a tachometer on it to see where you are  by ear.
Title: Re: Tuning a saw
Post by: 05_sprcrw on April 07, 2011, 04:20:28 pm
Is it a stock rebuild ? ported ? muff mod. only ? I think these will come into play as well. JMHO.

Steve

It is a stock rebuild. How do those come into play? Isn't the max rpms a saw can handle listed by the manufacturer so even if I modded it wouldn't I want to only tune it to factory specs. For this saw it is 12,500 rpms, if not then what can I safely go to with the saw, I plan on squishing the jug by taking out the gasket and using a gasket maker, and at most a muffler mod as well.
Title: Re: Tuning a saw
Post by: man of stihl on April 07, 2011, 05:36:55 pm
Factory specs mean nothing to me. As long as it is 4 stroking out of the cut at WOT. you will be ok.
Title: Re: Tuning a saw
Post by: Cut4fun . on April 07, 2011, 06:19:01 pm
Is it a stock rebuild ? ported ? muff mod. only ? I think these will come into play as well. JMHO.

Steve

It is a stock rebuild. How do those come into play? Isn't the max rpms a saw can handle listed by the manufacturer so even if I modded it wouldn't I want to only tune it to factory specs. For this saw it is 12,500 rpms, if not then what can I safely go to with the saw, I plan on squishing the jug by taking out the gasket and using a gasket maker, and at most a muffler mod as well.

Just say a stock 372xp is set at 13.5K max wot rpm. I have seen woods ported ones hitting 15K-17K out of the wood and the plugs look perfect. 
Now I would prefer to be on the rich side and clear up in the cut for cutting wood all day.
Title: Re: Tuning a saw
Post by: 05_sprcrw on April 08, 2011, 07:45:21 am
Is it a stock rebuild ? ported ? muff mod. only ? I think these will come into play as well. JMHO.

Steve

It is a stock rebuild. How do those come into play? Isn't the max rpms a saw can handle listed by the manufacturer so even if I modded it wouldn't I want to only tune it to factory specs. For this saw it is 12,500 rpms, if not then what can I safely go to with the saw, I plan on squishing the jug by taking out the gasket and using a gasket maker, and at most a muffler mod as well.

Just say a stock 372xp is set at 13.5K max wot rpm. I have seen woods ported ones hitting 15K-17K out of the wood and the plugs look perfect. 
Now I would prefer to be on the rich side and clear up in the cut for cutting wood all day.

Ok got you, at that point is it a combo of playing it by ear and seeing what you can get away with or is it something that experienced guys just know?
Title: Re: Tuning a saw
Post by: 05_sprcrw on April 08, 2011, 07:46:10 am
Factory specs mean nothing to me. As long as it is 4 stroking out of the cut at WOT. you will be ok.

Ok thanks I will make sure that it is doing that.
Title: Re: Tuning a saw
Post by: sharkey on April 08, 2011, 05:04:37 pm
After a rebuild I use heat cycles for stress relief. 

First time running a new piston, rings, bearings and cylinder in I double the oil in the fuel.  Start the saw, adjust the idle speed and set the engine to run for 10-15 min.  Once cool the unit then goes back up on the bench and I recheck all the fastners. 

For cycle two I keep the carburetion rich and begin to dial in the top speed and transition settings.  I set the top rich for a good four stroking.  Again allow to cool and then back to standard mixed fuel and final load based dial in from there.       

Just wanted to pass this along in case you have not heard of this method.  I really cringe when I see a newly rebuilt or brand new engine reved up when cold and put to the wood under full load.  Somewhere its published that a three minute warm up doubles the service life of the engine.       
   
Title: Re: Tuning a saw
Post by: 05_sprcrw on April 11, 2011, 10:06:15 am
Thanks I had not herd of that and I definitely kept it really rich and did warm it up before going full throttle and it is going strong. I am hoping to tune it this coming weekend for final cutting speeds if all goes well.
Title: Re: Tuning a saw
Post by: HolmenTree on April 11, 2011, 11:16:04 am
Yes it does take experience to hear that sweet spot at WOT. But once you hear it with your one particular saw you will never forget it.Get a stop watch, a clean even sized log or timber [cant] with no knots.

With your L, idle and H screws set by the owners manuals specs.Have a clean air filter. Warm your saw up with a couple of warm up cuts, then make 2 cuts each cut timed by a helper. Write them down. Then lean  [turn in] the H screw a micro click and time 2 more cuts. Keep doing this until the time starts to get slower. There you have found your sweet spot at the last H setting, while still warm rev the saw at WOT a few seconds at a time and get used to hearing that sound.

Willard.
Title: Re: Tuning a saw
Post by: Iron City on April 11, 2011, 03:13:59 pm
I've never heard the term WOT used.  What does it stand for?  I'm guessing wide open trottle.
Title: Re: Tuning a saw
Post by: HolmenTree on April 11, 2011, 04:50:10 pm
I've never heard the term WOT used.  What does it stand for?  I'm guessing wide open trottle.
You got it.
Title: Re: Tuning a saw
Post by: Iron City on April 11, 2011, 05:09:13 pm
Thank you.
Title: Re: Tuning a saw
Post by: Al Smith on April 12, 2011, 05:17:46 am
Strictly my opinion but a tach is not the ultimate tool in tuning .Nice to have but not as good as an ear .

Once you  do some modifications to an engine those factory RPM specs don't apply any more .That plus the fact that no two saw engines run exactly the same .
Title: Re: Tuning a saw
Post by: 05_sprcrw on April 12, 2011, 08:34:47 am
Yes it does take experience to hear that sweet spot at WOT. But once you hear it with your one particular saw you will never forget it.Get a stop watch, a clean even sized log or timber [cant] with no knots.

With your L, idle and H screws set by the owners manuals specs.Have a clean air filter. Warm your saw up with a couple of warm up cuts, then make 2 cuts each cut timed by a helper. Write them down. Then lean  [turn in] the H screw a micro click and time 2 more cuts. Keep doing this until the time starts to get slower. There you have found your sweet spot at the last H setting, while still warm rev the saw at WOT a few seconds at a time and get used to hearing that sound.

Willard.

Thanks for all your help guys, I appreciate all this, and taking it all in. 

I will give this a try and see how it goes as well.
Title: Re: Tuning a saw
Post by: Al Smith on April 13, 2011, 11:04:29 am
Another little tip is to "read " the plug .Properly tuned it should have a slight brownish tint to it .Too rich is black and too lean will be whiteish .It's always better to err on the side of caution and be too rich as too lean .

Pretty simple .Clean the plug, run the saw hard for 10 15 minutes .Let it cool off and check it .
Title: Re: Tuning a saw
Post by: Cut4fun on April 13, 2011, 01:21:02 pm
Reading a plug.

Chart for those not knowing how or what to look for.

http://www.dansmc.com/spark_plugs/spark_plugs_catalog.html

http://www.verrill.com/moto/sellingguide/sparkplugs/plugcolorchart.htm
Title: Re: Tuning a saw
Post by: 05_sprcrw on April 14, 2011, 07:58:27 am
I do know how to read a plug (assuming its similar to a regular vehicle spark plug).  Thanks for all the tips this is the first time I have really done a complete tune myself instead of just minor adjustments and appreciate all the help I have received.
Title: Re: Tuning a saw
Post by: HolmenTree on April 14, 2011, 11:57:57 am
Most times reading a plug does not prevent damage because when you figure out the problem with the color the damage is already done.
Another good advice is when reving a saw to WOT out of the cut, is don't blip the throttle up and down to WOT quickly. Its OK to blip the throttle to WOT quickly, but let off the throttle trigger "slowly" back to idle. This saves alot of stress on the connecting rod bearings.

Willard. 
Title: Re: Tuning a saw
Post by: 05_sprcrw on April 18, 2011, 07:24:58 am
Thanks I did not know that, I have used saws for a long time just never took the time to learn the internal workings or complete tare downs until now.  Forums like this sure make it seem a whole lot less daunting.
Title: Re: Tuning a saw
Post by: 05_sprcrw on May 04, 2011, 12:45:06 pm
Just wanted to let everyone know I got a good grasp of things now and have the saw tuned nicely and hope to do some cutting with it this weekend.