Four stroking a two stroke?

[ROBERT F]

Ok, maybe a dumb/weird question, but why would anyone want their two stroke to run so poorly at wot that it skips every other combustion cycle? been reading lots of threads lately with people saying to "make sure your saw is four stroking......". I can see using four stroking as a guide to understand rich high limits, then leaning out from there to get max power output at max rpms, but why would you want to dump one combustion cycle every other time? wouldnt that foul plugs, waste fuel, and just cause poor cutting performance at wot, where a saw is supposed to be run? Just asking cause ive always ran lean just below the fourstroking limit, and have yet to have problems. Fourstroking by def. is when a two stroke engine is running so rich that combustion takes two cycles to complete. wich causes that reduction in speed, and power output that causes the pitch of the engine to change. Whats the thoughts of the tuning experts out there in hearth world?

 

[wendell]

Because you don't run at WOT when you are working so if you get four stroking when you are, you will be running perfectly when you are cutting and getting a richer mixture and cooler operating temps.

 

[smokinj]

http://web.archive.org/web/20051018212959/www.madsens1.com/sawtune.htm the site will be back up at 10:00 listen to the sound wave

 

[GrantC]

The proper tune for a chainsaw is to run it rich enough to four-stroke at WOT with NO LOAD, but to smooth out the instant load is applied. This is an important concept.

As load is applied, and as the cylinder heats, the engine runs leaner. In a large cut, there can be a substantial difference in mixture between the beginning of the cut and the end.

By tuning rich with no load, as it leans under load the mixture will become just right, which produces peak working HP.

If the saw is tuned so that it doesn't four-stroke at WOT/no load, the instant it starts the cut it will be running lean, and by the end of the cut may be running extremely lean. It will not be making peak HP in wood, and will be running hotter than it should.

Tuning properly means to four-stroke at WOT and "clean up" just as the cut starts. It gives you the best performance and maximizes the life of your engine.

 

[PapaDave]

Ok, maybe a dumb/weird question, but why would anyone want their two stroke to run so poorly at wot that it skips every other combustion cycle? been reading lots of threads lately with people saying to "make sure your saw is four stroking......". I can see using four stroking as a guide to understand rich high limits, then leaning out from there to get max power output at max rpms, but why would you want to dump one combustion cycle every other time? wouldnt that foul plugs, waste fuel, and just cause poor cutting performance at wot, where a saw is supposed to be run? Just asking cause ive always ran lean just below the fourstroking limit, and have yet to have problems. Fourstroking by def. is when a two stroke engine is running so rich that combustion takes two cycles to complete. wich causes that reduction in speed, and power output that causes the pitch of the engine to change. Whats the thoughts of the tuning experts out there in hearth world?

My Husky manual states, "When the carb is correctly adjusted the machine accelerates without hesitation and the machine 4-cycles a little a max speed." Doesn't explain what it is, but gives general instruction on how to adjust.
I thought I had read the manual, but I missed that when I got the saw. Now I need to go adjust it after the break-in.............2.5 years later! DOH!
Funny thing is, it runs great.

Dave

 

[smokinj]

Ok, maybe a dumb/weird question, but why would anyone want their two stroke to run so poorly at wot that it skips every other combustion cycle? been reading lots of threads lately with people saying to "make sure your saw is four stroking......". I can see using four stroking as a guide to understand rich high limits, then leaning out from there to get max power output at max rpms, but why would you want to dump one combustion cycle every other time? wouldnt that foul plugs, waste fuel, and just cause poor cutting performance at wot, where a saw is supposed to be run? Just asking cause ive always ran lean just below the fourstroking limit, and have yet to have problems. Fourstroking by def. is when a two stroke engine is running so rich that combustion takes two cycles to complete. wich causes that reduction in speed, and power output that causes the pitch of the engine to change. Whats the thoughts of the tuning experts out there in hearth world?

My Husky manual states, "When the carb is correctly adjusted the machine accelerates without hesitation and the machine 4-cycles a little a max speed." Doesn't explain what it is, but gives general instruction on how to adjust.
I thought I had read the manual, but I missed that when I got the saw. Now I need to go adjust it after the break-in.............2.5 years later! DOH!
Funny thing is, it runs great.

Dave

the lenght will be back up after while and it has a sound machine so you can hear it but to me it sound like the machine is skiping a beat and 2 cycle sounds perfect

 

[PapaDave]

The proper tune for a chainsaw is to run it rich enough to four-stroke at WOT with NO LOAD, but to smooth out the instant load is applied. This is an important concept.

As load is applied, and as the cylinder heats, the engine runs leaner. In a large cut, there can be a substantial difference in mixture between the beginning of the cut and the end.

By tuning rich with no load, as it leans under load the mixture will become just right, which produces peak working HP.

If the saw is tuned so that it doesn't four-stroke at WOT/no load, the instant it starts the cut it will be running lean, and by the end of the cut may be running extremely lean. It will not be making peak HP in wood, and will be running hotter than it should.

Tuning properly means to four-stroke at WOT and "clean up" just as the cut starts. It gives you the best performance and maximizes the life of your engine.

GrantC,
GREAT info., thanks. Been on this forum for a while now, and still manage to learn stuff.

Dave

 

[LLigetfa]

Ja, sounds like you missed the part about no load WOT versus under heavy load in the cut. The saw should smooth right out when you load it heavy. In fact you should feel the power curve come on strong with an increase of RPM. I love that sound and feeling! The richness of the mixture also acts a governor, keeping down the RPMs when not under load.

 

[GrantC]

It should be noted that the proper way to check for tune is immediately AFTER a cut, when the saw is at its leanest.

Here's a good video of tuning by Brad Snelling, an expert at the job:



In the first cut he's running just a tad rich; it's occasionally four-stroking under load. A quick adjustment, and you'll note that the saw is cutting faster. Also note that the saw goes from smooth to four-stroke as soon as he removes the load - the way it should be.

 

[smokinj]

It should be noted that the proper way to check for tune is immediately AFTER a cut, when the saw is at its leanest.

Here's a good video of tuning by Brad Snelling, an expert at the job:



In the first cut he's running just a tad rich; it's occasionally four-stroking under load. A quick adjustment, and you'll note that the saw is cutting faster. Also note that the saw goes from smooth to four-stroke as soon as he removes the load - the way it should be.

Thats brad with a bb 440 very strong saw,he modds saw for a living if you need one none he is one of the best

 

[ROBERT F]

It would appear that i have been running my saws just a tad lean then. As i would tune them to where they would fourstroke at wot, no load, then lean it out just a smidge so that it just barely would fourstroke. I think my fault came in the fact that my training came from water cooled two stroke bikes. Very littlle experience with air cooled two strokes other than some 70's models vintage type bikes, and the saws, and nitro r/c motors but they all tune diferent. looks like I need to brush up on my saw tuning. Thanks for all the insite. I will have to see how much faster they cut when operating at true peak power.

 

[GrantC]

For me, it's not so much about cutting faster....it's about making my saw last longer!

-=[ Grant ]=-

 

[ROBERT F]

well I guess i havent been doing that bad, as I have a well used homelite and pull-on, both of them reqiure tuning at the harvest site, then again at home to process. 10,500+ft vs 6500 ft elevation. And I have not "burnt down" an engine yet. The Husky seems to run equally well at both elevations, so tunning on that one is only once a year. all saws run the same plug all season, and then gets replaced next season.

 

[smokinj]

well I guess i havent been doing that bad, as I have a well used homelite and pull-on, both of them reqiure tuning at the harvest site, then again at home to process. 10,500+ft vs 6500 ft elevation. And I have not "burnt down" an engine yet. The Husky seems to run equally well at both elevations, so tunning on that one is only once a year. all saws run the same plug all season, and then gets replaced next season.

yep living in CO I would think you could tune anything in your sleep, elevation can mess with the best of saws

 

[smokinj]

It would appear that i have been running my saws just a tad lean then. As i would tune them to where they would fourstroke at wot, no load, then lean it out just a smidge so that it just barely would fourstroke. I think my fault came in the fact that my training came from water cooled two stroke bikes. Very littlle experience with air cooled two strokes other than some 70's models vintage type bikes, and the saws, and nitro r/c motors but they all tune diferent. looks like I need to brush up on my saw tuning. Thanks for all the insite. I will have to see how much faster they cut when operating at true peak power.

that is the way to do it, unless its 4 stroking in the cut

 

[billb3]

I've always called that 'four stroking' 'buzzing' and avoided it .
Not so much for saw longevity, but just obvious it cut better and 'sounded right'.