Stihl gas powered equipment--rev limit increase?

   / Stihl gas powered equipment--rev limit increase? #1  

TractorLegend

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Location
Randle, WA
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2012 DK 45HST SE w/ FEL
I have a BR550 gas backpack leaf blower I just bought---it seems it should run at a bit higher rpm for the power to be as expected.
Also I have a Stihl chain saw with same issue---it seems for safety they keep the rpm's too low at wide open throttle.
Does anyone know how to increase rev limit a few hundred rpm on these??
I'm mechanically ept but I havent dissected either yet---just looking for been there-done thats... Thanks
 
   / Stihl gas powered equipment--rev limit increase? #2  
A lot of the time the little screen on the exhaust outlet is plugged. If you take it off and clean it, the RPM will go up. I don't know if this is the problem with yours or not but it is something to look at.
 
   / Stihl gas powered equipment--rev limit increase?
  • Thread Starter
#3  
The equipment is pretty new and this condition is the same ---not a deterioration.
I think saw shops in logger towns know how to amp these up?
Muffler mods??
 
   / Stihl gas powered equipment--rev limit increase? #4  
First, as suggested, clean the exhaust screen. Also clean the air filter... I don't know about the blower, but on a chain saw, they can get full of debris pretty quickly. If you still don't have the power, you can adjust the mixture for max RPM... almost any chain saw sales/servic facility can adjust this for you. It's also not too difficult to do yourself, once you know what to listen for when tuning it (at least on the 2-cycle chain saw engines... I've not messed around with the 4 cyle engines on some of these things). A word of warning: setting these incorrectly is a good way to destroy an engine. Those chainsaw engines are cranking out a lot of power for their size as it is.

A lot of these engines used to ship with the mixture set intentionally rich. This would help the saw run a bit cooler during the first tank or two of gas while it was breaking in. If you have one that was set up this way, that could explain why you don't have the power you expect. I believe some of the newer saws have limits on the mixture setting to prevent it from being set very rich (to meet emissions standards).

John Mc
 
   / Stihl gas powered equipment--rev limit increase?
  • Thread Starter
#5  
On the leaf blower---its just a 50cc 2 stroke bought today---the screen has to be clean. The saw has about 20 hours total---it may be worth checking but it has been, in my mind, capable of much higher rpm even tho i'm only looking for a few hundred more. Heck, those dirt bikes rev up to the sky....
Im thinking along the lines of if theres a throttle stop set screw, or hogging out the muffler port, or something.
I realize the manufacturer sets them low for safety, durability, getting safely thru warranty ,etc.
I'm willing to risk a bit of this due to the relative little use they get...I just want performance!! Thanks for all input!!
(It feels too lean and possibly a throttle stop set too slow)
I wont tell the engineers if you don't....
 
   / Stihl gas powered equipment--rev limit increase? #6  
</font><font color="blue" class="small">( The saw has about 20 hours total---it may be worth checking but it has been, in my mind, capable of much higher rpm even tho i'm only looking for a few hundred more. Heck, those dirt bikes rev up to the sky....
Im thinking along the lines of if theres a throttle stop set screw, or hogging out the muffler port, or something.
I realize the manufacturer sets them low for safety, durability, getting safely thru warranty ,etc. ...
(It feels too lean and possibly a throttle stop set too slow)
I wont tell the engineers if you don't.... )</font>

I don't know if there is a throttle stop limit on your chainsaw or not, but if the mixture is off, that will definitely affect the RPMs you are getting. Another thing you can do is change out the drive sprocket to gear your chain up faster. Some of the professional loggers around here do that with brand new saws... others wait until their drive sprocket has worn to the point where it needs replacement, then swap it out. I know this is done on the higher-end Jonsered and Husqvarna models (the drive sprocket is a different design on th elower end models, so I don't know what the options are there). I assume you can do something similar on the Stihl.

Barring significant changes like the sprocket, the best things you can do to imrpove cutting power: keep air filter clean, adjust mixture appropriately, and keep your chain sharp, and put on a good chain (some of the ones they ship with are poor performers, especially when trying to do a bore cut... designed more for low kickback than max performance).

If all else fails, buy a saw with a bigger engine (insert "Tim the Toolman" grunts here...)

John Mc
 
   / Stihl gas powered equipment--rev limit increase? #7  
Your oil mix can slow it down as well. If the ratio is supposed to be 50:1 and your mixing 40:1, 32:1 etc.. the extra oil will slow it down as well.
 
   / Stihl gas powered equipment--rev limit increase? #8  
I used to maintain small two stroke equipment for a local golf course. All of the above are good suggestions. I used to adjust the high speed mixture by ear - meaning fine tune the jet until max rpm is acheived and then open it up approx 1/4 +/- turn more until the rpm starts to drop off a bit so it will run slightly rich. What used to happen with the golf maintenance crew is that they would hold the throttles wide open - leaf blowers, brush cutters etc and the aluminum piston and rings would melt together. By having the high speed jet (mixture screw) set slightly rich you are not sacraficing a lot of performance and are achieving a little safety on longevity of the engine. I'd rather clean the exhaust spark arrestor screen once or twice a season than repair/replace an engine. Hope this helps - good luck
 
   / Stihl gas powered equipment--rev limit increase? #9  
If I'm not mistaken, that BR550 is Stihl's new 4-Mix, which is essentially a 4-stroke. That may explain the low RPM's. Don't worry, it won't need to scream like a 2-stroke to make some good power.
 
   / Stihl gas powered equipment--rev limit increase? #10  
Now I'm confused - are they 4- stroke? I believe the 4-mix is 'still a two stroke but the mix is 50:1 for cleaner emmisions. Check out the Sthil website, there is a download for the manual. Also, the website shows a recall for that particular blower you may want to check out.
 

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