# Carb Tuning for Dummies



## WildnCrazyGuy (Nov 13, 2007)

Trying to simplify things a bit for carb tuning. I went from zero knowledge just a few months ago, to way too much knowledge at this point after reading all the posts on here regarding this subject. I mean if you read some of these tuning threads, it's a bit overwhelming. So, with my limited knowledge of tuning my 2 stroke equipment, saws, blowers, trimmers, etc., I wanted to check to see if I understand the concepts correctly, or if I need to adjust what I think I know and learn more. So here goes.

1. Begin with fresh fuel mix, clean air filter, check fuel filter, clean or new spark plug, clean muffler and spark arrestor.
2. Start with the L and H screws out from seat at about 1.5 turns for most 2 stoke carb applications.
3. Begin with idle, L, and LH or T or whatever opens the butterfly and adjust until idle is steady and continues to idle when turned every which way but loose. (Up, down, right, left, etc.) Then adjust the LH or T or whatever to keep the chain or clutch from spinning and continue to allow for proper idle. Turn it all around again to make sure it doesn't die. The L and LH together will allow for proper throttle response when the trigger is depressed. If there is lag or hiccup, then adjust the L leaner, clockwise toward seat until idle and throttle response is acquired.
4. End with turning the H to proper MAX rpm. Turn clockwise (right) to go faster (lean), turn counterclockwise (left) to go slower (rich).

If tuning by ear, then err on the slow side with H. Listen for the device to start to scream, then back it off until starts to have hard time keeping up, then put it somewhere in the middle.

If using a tach, as long as the desired idle rpm and max rpm are reached and the throttle responds well, is the saw pretty much tuned at this point? Is it possible with a tach to reach this effect (running great with the proper idle, response, and max rpm) with a saw or really any 2 stroke and run it lean, burn the piston if you stay below the MAX rpm for the saw or device? The only other thing I know to do is pop the spark plug after running a bit and see if it is dark and wet (rich), white (lean), or light tan (just right).

The reason I go through all this, I have a new TT-20K tach and it seems that I'm still dark and wet (rich), on a little Poulan from my testing this weekend. I can consistently rev to 12-12.5K and it still looks rich to me. Poulan gave me a MAX of 12K for the 2150. I've seen 12.6K as well for that model so I'm thinking the Poulan tech wanted me below by a bit for my own good. Rich is better than lean obviously, but wondering if I was off on any of my tuning methods. Started with my little $20.00 Poulan in case I blew it up. Now I need to move on to my Stihl's, so I want to make sure I'm on track with this method.

Also, when I pulled the plug on the 2150 Poulan, it was wet and dark (rich), but maybe it should be that way given that I only idled and revved the saw for a few seconds at a time while getting it to MAX rpm. Would it probably go more tan like it's supposed to if I were to actually get to run it in wood during normal course? Or, maybe while I was getting the settings right, it was rich and the plug didn't get enough time to clean itself when I did get the rpm's right. Much thanks for useful input.


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## rxe (Nov 13, 2007)

> 3. Begin with idle, L, and LH or T or whatever opens the butterfly and adjust until idle is steady and continues to idle when turned every which way but loose. (Up, down, right, left, etc.) Then adjust the LH or T or whatever to keep the chain or clutch from spinning and continue to allow for proper idle. Turn it all around again to make sure it doesn't die. The L and LH together will allow for proper throttle response when the trigger is depressed. If there is lag or hiccup, then adjust the L leaner, clockwise toward seat until idle and throttle response is acquired.



I'd change this a bit.

1) From factory idle settings, adjust the L screw to give max rpm. You will find that as you lean it out (screw it into the seat) the revs rise to a peak, then suddenly fall. The peak is a bit too lean - richen up quarter of a turn from the peak position. If the revs are too high for spec, close the idle screw a little bit (the one that stops the butterfly from closing, not the mixture screws. Leave the saw running for a minute, then flip it upside down - that will check for fuel pooling in the crankcase (too rich). If it dies when you flip it, lean the L screw out a little bit and try again.

2) Set the H mixture as you describe. I prefer to start rich, and gradually get the rpm up to spec, and because I'm a chicken, I always aim for 1000 rpm below spec.

3) If the saw does not respond well to the throttle from idle to WOT, it is probably a bit too lean at idle I think.


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## ShoerFast (Nov 13, 2007)

Very simply

Start the saw and set the 'T' just so the chain is turning. 

Smoothly run the 'L' in and out to get the best chain speed. 

Readjust the chain speed with the 'T' and reset the best 'L' 

Back the 'T' out till the chain stops creeping,,,,,and a tad more. 

If you feel comfortable * 'safely' set the 'H' a little richer or out from anything you think it will take. Set the saw over a log and with the chain very free from anything around it, hold it at 'WOT' while turning the 'H' in till it wails a (a real high-pitched scream) that is too lean,,,,quickly back it out till you get a 4-cycle burble (sounds choppy, rough uneven) then just in a very little to smooth the burble out. 

*No points for running a saw at WOT one-handed while adjusting the 'H' with the other,,,,,, try that if your comfortable. There are complete Professionals here that will not tweak a carb at WOT that way. 

Best way to set the 'H' is by doing timed cuts. Counting 1 Mississippi's, 2 Mississippi's till the cookie/block drops, is the best 'H' setting you can get. Best time in big wood (for the saw) is the best 'H' setting. Having a tach helps also, you can find your ball-park faster. 

Stay safe and have fun with it. There is nothing more fun then tossing a running saw down to do some work, come back to it and it rev's quickly to life and cuts it's fastest.


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## Cut4fun (Nov 13, 2007)

I have always like this one for beginners. Basic carb tuning by Madsen's link.

http://web.archive.org/web/20060316084604/www.madsens1.com/sawtune.htm


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