How do
How does the coil accomplish a rev limit. I worked automotive many years. Im curious
Makita dolkita dcs6421 rev limiter sound? Video clip
- Thread starter August76
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James Miller
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Its black magic. I really don't know how they do it.
Don't know where the 7910's like to run but the older stock 7900 would run a bit rich at 13,500 they liked to spin, awesome engines.
I think thr flywheels were timed different. I could be wrong.
Poleman
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I thought all the 64xx’s were limited to 13.5k, that’s why builders use them and put on the 79cc’s top ends so they don’t get stuck with the 12.8k coil!!??
The difference between the 7900-13.5 coils and the 7910-12.8, is they use a different flywheel. Looks the same (magnet location) just different ribbing. I’ve been told either will work, and that they won’t....I don’t know as I’ve never tried it, I just go the 272 route and am done with it.
Guess I shoulda tried it before I sold a stock 7910...have a box of coils I’ve replaced for unlimited.
The difference between the 7900-13.5 coils and the 7910-12.8, is they use a different flywheel. Looks the same (magnet location) just different ribbing. I’ve been told either will work, and that they won’t....I don’t know as I’ve never tried it, I just go the 272 route and am done with it.
Guess I shoulda tried it before I sold a stock 7910...have a box of coils I’ve replaced for unlimited.
Yeah the dcs6421 are all 13.5
These saws cut the fastest from 9000 to 9500 RPM and in this vid he is over revving it thus the 4 stroking in the cut. A unlimited coil will gain nothing besides easier tuning , tuning is easy start way rich then gradually back in until it cleans up in the wood. Steve
Poleman
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I disagree with parts of this...
Yes they may start easier with a limited coil, and they for sure are easier to tune but the most power at 9k to 9.5k is in the basement. I have a stock limited coil 7910 that turns 12,3k with a 28 inch bar full chisel in 24 inch Pine. The saw would only be half throttle at 9-9.5......and no way am I not cutting at WOT. My ported saws with unlimited coils all are faster than that and closer to 13k in the cut. No way is 9-9.5 optimal and faster.....they are more capable than that and that’s why their such a good saw.
Yes they may start easier with a limited coil, and they for sure are easier to tune but the most power at 9k to 9.5k is in the basement. I have a stock limited coil 7910 that turns 12,3k with a 28 inch bar full chisel in 24 inch Pine. The saw would only be half throttle at 9-9.5......and no way am I not cutting at WOT. My ported saws with unlimited coils all are faster than that and closer to 13k in the cut. No way is 9-9.5 optimal and faster.....they are more capable than that and that’s why their such a good saw.
James Miller
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What all is involved in the 272 swap? Sorry OP for the thread jack.
You should look at HP charts on saws, every stock saws makes the most HP from 9000 to just over 9500 RPM and the HP falls off fast after that, a ported saw might make the most HP around 10000 RPM . Your just fooling yourself and cutting slower if your running them at 12500 in the cut, most any saw will run at 12500 in the cut if not enough pressure is applied but you will be cutting slower. Steve
Poleman
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Steve, aperently you get your saw knowledge off the inter screen and magazines unlike mine I get in the woods. I’ll gareentee you’ll have to hang onto any of my saws in a cut or you’ll get pulled into the tree....my chains are sharp and I dog in.
I’ve learned a long time ago what you tead in a magazine or reed in store on specs you need to take with an open mine as most of them are stretched and off the mark. Weights are different, hp ratings are different......
And as far as fooling myself I will check with a tac to see what my rpms are....it’s NOT a guess.....and again....my chains notbsidding on top spinning....
James, look up “Cheap Dolmar 7900 coil swap” on this site. It was from quite awhile ago but gives details....and if you have questions just PM me and I’ll walk you through and road blocks.
A 272 coil and some time is all that’s needed. Unscrew the coil wire off the Dolmar coil and drew it on the 272 coil....tip: don’t mess with the clips that hold the plug wire in originally....just unscrew....a lot easier, quicker and plug wire stays secure....a little iffy after you mess with the clips.....don’t ask how I know....
I’ve learned a long time ago what you tead in a magazine or reed in store on specs you need to take with an open mine as most of them are stretched and off the mark. Weights are different, hp ratings are different......
And as far as fooling myself I will check with a tac to see what my rpms are....it’s NOT a guess.....and again....my chains notbsidding on top spinning....
James, look up “Cheap Dolmar 7900 coil swap” on this site. It was from quite awhile ago but gives details....and if you have questions just PM me and I’ll walk you through and road blocks.
A 272 coil and some time is all that’s needed. Unscrew the coil wire off the Dolmar coil and drew it on the 272 coil....tip: don’t mess with the clips that hold the plug wire in originally....just unscrew....a lot easier, quicker and plug wire stays secure....a little iffy after you mess with the clips.....don’t ask how I know....
Lol. No worries i want to know also. I like learning stuff about these saws
This saw is pretty amazing just stock. Mine's not doing too good because the stupid bar is all screwed up and I'm making crooked cuts it gives that feeling like the bar is being pinched while you're cutting cuz the cut is moving all over the place in a big log
This saw is pretty amazing just stock. Mine's not doing too good because the stupid bar is all screwed up and I'm making crooked cuts it gives that feeling like the bar is being pinched while you're cutting cuz the cut is moving all over the place in a big log
Little Al
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Got to agree with that set the mixture screws first then try with a couple of 3/4 secs WOT bursts out of wood ,should sound like a misfire
(And as far as fooling myself I will check with a tac to see what my rpms are....it’s NOT a guess). If you check with a tach you'll find you'll cut the fastest right around 9500 RPM/
(And as far as fooling myself I will check with a tac to see what my rpms are....it’s NOT a guess) If you actually check with a tack you'll fid you cut the fastest around 9500 RPM where the most power is.
I get my knowledge from running saws around the sawmill and find if you let them scream they cut slower as proved by many vids on here. No bs here. Steve
Poleman
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Still disagree with you on cutting speed....9500 is spec for a 30 year old saw with max rom of 12-12.5.
So your telling me if I’m in the wood turning 12.5+ I’m cutting slower than 9.5k you are saying??? That’s doesn’t even make sense and your only looking at factory specs coming from the factory who inflate or reword some of their specs to make them look better in the consumers eyes. They also give number with a built in safety margin to protect there equipment they sell who in the hands of John Q. Public trash it first outing.
Factory numbers are their guidelines. Weights differ, HP ratings differ all because of the way they are derived......one company does it one way an other company does it different....thus scewed results and facts.
Ok, so you run saws around a Sawmill where someone has adjusted a saw so lean it has no power....ya it sounds good but put it in wood and it dies......and will from a lean seize at some point.
What we are talking about here are saws that are tuned correctly and still leaving power on the table like a lot of limited saws. The 7910 being what we’re discussing here. Being limited at 12,8 you need to know how to adjust in the wood or it will never be at its optimum. In my opinion of what the OP is showing in the video.
So your saying running over 9,5 is a waste because the factory says.... you can’t always go with and believe what factory specs say....to many variables....altitude, oil used, fuel used, mix ratio, tune, chain, length of bar and air cleaner maintenance. Probably more too.
No way are you going to convince me a saw that’s tuned correctly running 9,5 will out cut a correctly tuned saw turning 12,5 with all variables being the same, bar, chain etc. That’s total dark age thinking. I’ll guarantee the 12,5 will drop out of the log first.
So your telling me if I’m in the wood turning 12.5+ I’m cutting slower than 9.5k you are saying??? That’s doesn’t even make sense and your only looking at factory specs coming from the factory who inflate or reword some of their specs to make them look better in the consumers eyes. They also give number with a built in safety margin to protect there equipment they sell who in the hands of John Q. Public trash it first outing.
Factory numbers are their guidelines. Weights differ, HP ratings differ all because of the way they are derived......one company does it one way an other company does it different....thus scewed results and facts.
Ok, so you run saws around a Sawmill where someone has adjusted a saw so lean it has no power....ya it sounds good but put it in wood and it dies......and will from a lean seize at some point.
What we are talking about here are saws that are tuned correctly and still leaving power on the table like a lot of limited saws. The 7910 being what we’re discussing here. Being limited at 12,8 you need to know how to adjust in the wood or it will never be at its optimum. In my opinion of what the OP is showing in the video.
So your saying running over 9,5 is a waste because the factory says.... you can’t always go with and believe what factory specs say....to many variables....altitude, oil used, fuel used, mix ratio, tune, chain, length of bar and air cleaner maintenance. Probably more too.
No way are you going to convince me a saw that’s tuned correctly running 9,5 will out cut a correctly tuned saw turning 12,5 with all variables being the same, bar, chain etc. That’s total dark age thinking. I’ll guarantee the 12,5 will drop out of the log first.
Poleman
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James and August76 drop me a PM if you’d like to more about the swap to the 272 coil.
https://www.manualslib.com/manual/811038/Dolmar-Ps-6400.html?page=3#manual
Read this chart, what rpm does a 7900 make the most power, in case you cant it's 9500 rpm as I said. And don't give me any bs that they make more power at 12500 rpm, they don't or Dolmar would print it. Saws are going to cut the faster right where they make their peak HP if. You say you run a sharp chain and dog in, with my sharp chains they self feed and make the saw work in its power range. . Enough of this bs high rpm in the cut. Steve
Poleman
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Sorry but I’m NOT BELIEVING YOUR BS..... your just a chart quoted and NO practical experiance...
Right Steve no more of you BS because your GULL OF IT AND YOURSELF....
You apparently know everything and all....oh master.....you need to get in the real world Ana’s reality....you have NO CLUE what your saying and only quoting specs and charts.
Enough of your crap......
Right Steve no more of you BS because your GULL OF IT AND YOURSELF....
You apparently know everything and all....oh master.....you need to get in the real world Ana’s reality....you have NO CLUE what your saying and only quoting specs and charts.
Enough of your crap......
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