Dolmar 7900 Coil Limiter... Why

Jtheo · Aug 15, 2009

I have done a google search and as of now there does not seem to be an unlimited coil available.

The question I have is : Is the limited coil part of an effort to meet EPA regs, or is there some other reason?

It seems to me that the limited coil keeps the saw from developing full power, but I might not understand the process.

Wish I knew the reason, and I am sure a lot of the guys here do know the reason.. Thanks

mountainlake · Aug 15, 2009

Jtheo said:
I have done a google search and as of now there does not seem to be an unlimited coil available.

The question I have is : Is the limited coil part of an effort to meet EPA regs, or is there some other reason?

It seems to me that the limited coil keeps the saw from developing full power, but I might not understand the process.

Wish I knew the reason, and I am sure a lot of the guys here do know the reason.. Thanks

These saws turn 9 to 10 thousand RPM when cutting and a limited coil has no effect whatsoever, make tuning them a little harder as one can mistake the limited coil for 4 stroking and set it to lean. Steve

Zombiechopper · Aug 15, 2009

a limited coil is used to prevent reving too high when the engine is not under load. It makes no difference at all when actually cutting but you need to tune in the wood to get the best tune on the saw.

rahtreelimbs · Aug 15, 2009

mountainlake said:
These saws turn 9 to 10 thousand RPM when cutting and a limited coil has no effect whatsoever, make tuning them a little harder as one can mistake the limited coil for 4 stroking and set it to lean. Steve

Zombiechopper said:
a limited coil is used to prevent reving too high when the engine is not under load. It makes no difference at all when actually cutting but you need to tune in the wood to get the best tune on the saw.

Bingo.......absolutely no reason for it!!!

Jtheo · Aug 15, 2009

Zombiechopper said:
a limited coil is used to prevent reving too high when the engine is not under load. It makes no difference at all when actually cutting but you need to tune in the wood to get the best tune on the saw.

That answers another question that was on my mind.

Since I joined this forum, I have learned a lot from the good folks here. One thing I learned was that I needed to get off my butt and learn how to tune my saws. I have learned to do it with a lot of help from a good friend.

But... trying to tune the 7900 with a tach, the RPM are just jumping all over. 9000, 12000. maybe back to something in between. My friend tunes by ear, but I have too much of a hearing loss to do that.

Jtheo · Aug 15, 2009

rahtreelimbs said:
Bingo.......absolutely no reason for it!!!

So why does Dolmar use a limited coil? They think someone is going to hold one WOT and blow it up?

Metals406 · Aug 15, 2009

Jtheo said:
So why does Dolmar use a limited coil? They think someone is going to hold one WOT and blow it up?

Yup. . . It limits the max RPM's so folks don't blow the saw up. Don't know why they'd care? The more saws guys blow up, the more the manuf. would sell.

Saw Dr. · Aug 15, 2009

Metals406 said:
Yup. . . It limits the max RPM's so folks don't blow the saw up. Don't know why they'd care? The more saws guys blow up, the more the manuf. would sell.

Supposing they were out of warranty when they blew.

Metals406 · Aug 15, 2009

B200Driver said:
Supposing they were out of warranty when they blew.

Correct, the saw buyer would have to ruin things right out of the gate.

brncreeper · Aug 15, 2009

Why limited coils?

From a company's standpoint it kills three birds with one stone:

1.It helps the company meet EPA regs.

2.Now the company will probably never have to replace a blown engine under warranty.

3.makes it nearly impossible to tune properly, so chances are when the warranty is up, so are the piston/cylinder/rings. OEM parts are costly so again the company wins.

blsnelling · Aug 15, 2009

Jtheo said:
But... trying to tune the 7900 with a tach, the RPM are just jumping all over. 9000, 12000. maybe back to something in between.

That's because you're into the rev limiter. Also, you can't tune the 7900 by ear at WOT. You'll have to do it in the wood. It's the only way you can tune one of these.

blsnelling · Aug 15, 2009

Is anyone looking into selling a direct bolt-on replacement unlimited coil? One that doesn't require degreeing in the flywheel without a key in the flywheel.

Andyshine77 · Aug 15, 2009

The best way to tune a saw with a limited coil is in the wood, like others have said. I made this video to give people a good idea how it's done.

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4mocajuns · Aug 15, 2009

blsnelling said:
That's because you're into the rev limiter. Also, you can't tune the 7900 by ear at WOT. You'll have to do it in the wood. It's the only way you can tune one of these.

So what should I be listening for when in the wood? Surely not 4 stroking and not max rpm so what then?

Andyshine77 · Aug 15, 2009

4 Stroking sounds completely than when the limiter kicks in. If you put the saw under load you can tune the saw based on weather or not it's 4 stroking, like I did in the vid.

4mocajuns · Aug 15, 2009

Andyshine77 said:
The best way to tune a saw with a limited coil is in the wood, like others have said. I made this video to give people a good idea how it's done.

<object width="425" height="344"><param name="movie" value="http://www.youtube.com/v/ulY5sU4axFQ&hl=en&fs=1&"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="http://www.youtube.com/v/ulY5sU4axFQ&hl=en&fs=1&" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="425" height="344"></embed></object>

I am having trouble picking up on what I should be hearing. Can you expound?

4mocajuns · Aug 15, 2009

So you tune the same just under load.... not free spinning. So 4 stroke then lean her out just a little right?

Andyshine77 · Aug 15, 2009

The difference is a pretty clear burble when I first start cutting. As I lean the carb out, you start to hear the saw go back and fourth between the clean 2 stroke sound, and rough 4 stroke sound.

Andyshine77 · Aug 15, 2009

4mocajuns said:
So you tune the same just under load.... not free spinning. So 4 stroke then lean her out just a little right?

Correct. In a small log you want just a hair of burble, in a bigger log it should run without much or any burble. The best way to tune the saw is with the saw warmed up and with the bur buried.

4mocajuns · Aug 15, 2009

Thanks..... I have a 15 inch soft maple log out back to work with. As it is I timed my 361 against the 7900 and the times were 361...13.16 sec. 7900...9.76 sec. Maybe my 7900 is tuned pretty close right now.

Dolmar 7900 Coil Limiter... Why

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