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Dolmar 7910 Muffler scavenging -ditch -keep

Simondo

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The internals in the muffler of a 7910 that give " The Scavenging Reduction........ "
Whats the thoughts on leaving them intact with a saw that is not having any cylinder work.
Maybe just a littler exit hole increase ,but just leaving well alone inside the muffler itself.
There a bit of work to open and mod so as some have found ( myself included ) on the 6100 when no port work is being done there seems little or no benefit on removing the innards.
The 7910 gets a fuel saving from the standard muffler so maybe you just get more noise , no real power increase like with the 6100 and lose out on the fuel consumption benefit .
Anyone have anything they can put on the table ?
 
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Wilhelm

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Dolmar PS-7900 hollow muffler birdcage only = 6.2HP
Dolmar PS-7910 SLR muffler = 5.7HP

That's a lot of power to go missing!

I have the feeling that my PS-7900 loves a free flowing muffler.
I have a unmodified muffler on my PS-6400, considered many times to swap muffler's forth and back on my PS-7900 - never really got to it.

True, reducing back pressure will increase fuel consumption.
My PS-7900 is a thirsty beast.
 

Simondo

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Dolmar PS-7900 hollow muffler birdcage only = 6.2HP
Dolmar PS-7910 SLR muffler = 5.7HP

That's a lot of power to go missing!

I have the feeling that my PS-7900 loves a free flowing muffler.
I have a unmodified muffler on my PS-6400, considered many times to swap muffler's forth and back on my PS-7900 - never really got to it.

True, reducing back pressure will increase fuel consumption.
My PS-7900 is a thirsty beast.
Hi there Wilhelm.
There is a drop in max rpm on the 7910 from the different coil (limited )...Max free rpm 12800 rpm ( under load ,different matter) ....I believe there is a carb change to from 7900 to 7910 as well.
Im looking at the 7910 muffler with a open mind that on this Non Ported saw doing a muffler mod may not be a automatic thing to give more power .
 

Wilhelm

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Coil is limited only 700rpm lower on the PS-7910 - that is no load max WOT.
I kinda doubt the coil is swallowing 0.5HP.

Interestingly the PS-7310 didn't lose as much over the PS-7300.
Lesser amount of exhaust gases due to smaller combustion chamber generating lesser back pressure?
Who knows.

If I had a log worthy of my PS-7900 I'd try swapping the unmolested muffler from my PS-6400 onto her in an attempt to figure out whether there is any benefit from freeing the muffler flow up.
That is actually the only reason why I haven't touched my PS-6400's muffler yet, to have a stock muffler to test the muffler mod benefits theory.

Both my saws are stock internally, my PS-6400 is running a AM piston, and my PS-7900 has a mild muffler mod but was never dismantled.

I MMed my Sachs-Dolmar 108 - no benefits whatsoever.
The muffler wasn't restricted much, it had a ~4-5" long pipe going inside the muffler which I cut down to about 1", and a deflector that pushed the exhaust gases opposite of the muffler outlet which I grinded open for free flow both ways.
She's a 40cc 1,7kW saw from 1985., she's a bit tired and unfortunately the MM didn't help wake her up the least.

I have a couple clips on YouTube sporting my PS-7900, in some she's pulling her secondary 36" B&C setup with impressive authority - full comp round filed chisel chain.
Would be the perfect B&C setup to swap and test muffler's - but I got no log to bury a 36" bar into.

I like my PS-7900 with the MM I gave her, not too loud either.
My MM consists of enlarging the holes in the bird cage (didn't remove it completely) and enlarging the stock muffler outlet as much as possible without loosing the ability to still use the factory original screen. No secondary port added, muffler looks factory stock.

Noodled this with my PS-7900 & 36" B&C setup, oak log butt about 40" long meaning bar fully buried:
DSC02569.JPG
She didn't loose a single beat.
The surrounding trees were shaking out of fear they'd be next! :D
 

Simondo

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No one tried muffler work on the 7910 without port work as well i guess ??
 
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Wilhelm

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http://opeforum.com/threads/dolmar-6100-and-7910-muffler-mod-questions.4628/

Gutt muffler, widen existing muffler outlet, if You dare blend in the step and widen exhaust port on the cylinder.
If not ported second muffler outlet not needed.

That's what I got out of that thread anyways.

I hopefully have a 7310 incoming, if so I'll definitely take the SLR out.

As if I need any more saws with only 20ish logs a year to buck . . . :p
 

Simondo

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http://opeforum.com/threads/dolmar-6100-and-7910-muffler-mod-questions.4628/

Gutt muffler, widen existing muffler outlet, if You dare blend in the step and widen exhaust port on the cylinder.
If not ported second muffler outlet not needed.

That's what I got out of that thread anyways.

I hopefully have a 7310 incoming, if so I'll definitely take the SLR out.

As if I need any more saws with only 20ish logs a year to buck . . . :p
Yea...i saw that thread to. I am more interested in the SLR removal as a good or bad thing with a "completely " standard saw . Figured it had been tried on its own because like your comment in a earlier post , folks seem to see it as a big part of the power deferential between the 7900 and the 7910.
 

Wilhelm

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I see the SLR as a choke, even though my saws don't have one so I don't know how it makes the saw behave.

The way I see it the SLR seems to serve two goals, accommodating strickter exhaust regulations and lowering the noise level (by a decibel or two).
I read that the 7910's muffler outlet is smaller than on the 7900, add the SLR tube and the saw won't be all too happy.

My best guess is that the fuel savings are just a lucky side effect from choking the saw down, just as opening the muffler up increases fuel consumption - as does porting for that matter.

Any chance You could get Your hands on a spare 7310/7910 muffler, smashed or otherwise in rough shape, to play with?
 

Simondo

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I see the SLR as a choke, even though my saws don't have one so I don't know how it makes the saw behave.

The way I see it the SLR seems to serve two goals, accommodating strickter exhaust regulations and lowering the noise level (by a decibel or two).
I read that the 7910's muffler outlet is smaller than on the 7900, add the SLR tube and the saw won't be all too happy.

My best guess is that the fuel savings are just a lucky side effect from choking the saw down, just as opening the muffler up increases fuel consumption - as does porting for that matter.

Any chance You could get Your hands on a spare 7310/7910 muffler, smashed or otherwise in rough shape, to play with?
All logical points and observations you make there Wilhelm.
The 7910 /7310 are not a common saw here so new is the most likely way ...costly ! I will keep my eyes open though.
Be very interested as to what you make of the 7310 ...there always overlooked for the 7910 ...on a shorter bar set up helping to keep the weight lower they look like a fine saw .
 

Wilhelm

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All logical points and observations you make there Wilhelm.
The 7910 /7310 are not a common saw here so new is the most likely way ...costly ! I will keep my eyes open though.
Be very interested as to what you make of the 7310 ...there always overlooked for the 7910 ...on a shorter bar set up helping to keep the weight lower they look like a fine saw .
Someone here kinda quietly noted that the 7310 is only marginally, if at all, weaker than the 7910 - that intrigues me a little.

Didn't get any notification today regarding shipping/postage of the 7310 :( , will call tomorrow to check whether she's on her way to me or not.

As for the 7310 being a fine saw - I unconditionally love this saw family, therefore she'd fit in perfectly fine along my 6400 & 7900! :encama:

I am already eyeballing a PS-6400 in the Croatian classifieds.
I think I need one more of these to BB kit her to have the full range - 64cc, 73cc, 79cc & 84cc. :eusa_dance:

:pancarta:
 

Simondo

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Someone here kinda quietly noted that the 7310 is only marginally, if at all, weaker than the 7910 - that intrigues me a little.

Didn't get any notification today regarding shipping/postage of the 7310 :( , will call tomorrow to check whether she's on her way to me or not.

As for the 7310 being a fine saw - I unconditionally love this saw family, therefore she'd fit in perfectly fine along my 6400 & 7900! :encama:

I am already eyeballing a PS-6400 in the Croatian classifieds.
I think I need one more of these to BB kit her to have the full range - 64cc, 73cc, 79cc & 84cc. :eusa_dance:

:pancarta:
The power head is only 0.2kg (on paper ) up on a Husq 372 xp for a example (its class group) ...not to big a deal really , and with the same quoted HP/Kw. Power delivery and Torque may be a bit different to others in the class , but I doubt you will feel its underpowered or a fragile constructed saw . Putting it to work will be more telling than anything so i hope it gets to you ok. :)
 

Wilhelm

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Dolmar PS-7310 shipped yesterday by 48hrs. delivery, came in today before noon.

She's abused and in rough shape, but a little love and some parts 'n fixing and she'll be a head turner again.
Way of shipping a chainsaw very questionable as well, no cushioning material whatsoever - just a saw stuffed inside an empty duck-taped box.

Something (a hamfisted moron or a tree) bent the front handle to such an extend that it bent the (plastic) fuel tank anchoring as well.
DSC03036.JPG DSC03040.JPG DSC03100.JPG
Luckily no mayor mechanical damage.
I will try and bend the handle bar back and hope the fuel tank anchoring will bend back over time - if not I'll try and heat the section up a little.

The box she was shipped in - I almost freaked out when I looked inside:
DSC03027.JPG

Dumped the fuel and bar oil, poured in some of mine - she fired up, idled and blipped fine, oiler pushes oil OK (without bar attached).
Pulled the muffler, piston looks OK on the exhaust side.
Pulled spark plug, looks clean - neither rich nor lean.
All in all I got lucky purchasing this saw completely unseen! o_O

I'll fix her up.
I have a shopping cart pending from Dolmar Germany, I will add bits to make her a looker and runner again. :)

Muffler is SLR.
That crap needs to come out! :mad:

DSC03083.JPG
Just not a priority right now.

Adding Dolmar PS-7310 to my sig. :cool:
 
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Simondo

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Dolmar PS-7310 shipped yesterday by 48hrs. delivery, came in today before noon.

She's abused and in rough shape, but a little love and some parts 'n fixing and she'll be a head turner again.
Way of shipping a chainsaw very questionable as well, no cushioning material whatsoever - just a saw stuffed inside an empty duck-taped box.

Something (a hamfisted moron or a tree) bent the front handle to such an extend that it bent the (plastic) fuel tank anchoring as well.
View attachment 79017 View attachment 79018 View attachment 79020
Luckily no mayor mechanical damage.
I will try and bend the handle bar back and hope the fuel tank anchoring will bend back over time - if not I'll try and heat the section up a little.

The box she was shipped in - I almost freaked out when I looked inside:
View attachment 79021

Dumped the fuel and bar oil, poured in some of mine - she fired up, idled and blipped fine, oiler pushes oil OK (without bar attached).
Pulled the muffler, piston looks OK on the exhaust side.
Pulled spark plug, looks clean - neither rich nor lean.
All in all I got lucky purchasing this saw completely unseen! o_O

I'll fix her up.
I have a shopping cart pending from Dolmar Germany, I will add bits to make her a looker and runner again. :)

Muffler is SLR.
That crap needs to come out! :mad:

View attachment 79022
Just not a priority right now.

Adding Dolmar PS-7310 to my sig. :cool:
The shipping method is a big No No !! :eek:
With luck the price you paid makes the work you need to do less of a wallet buster ...the handle...were you told it was like that before you bought it?
You going to run it and see what you think before you do any muffler work Wilhelm.
 

Wilhelm

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The shipping method is a big No No !! :eek:
With luck the price you paid makes the work you need to do less of a wallet buster ...the handle...were you told it was like that before you bought it?
You going to run it and see what you think before you do any muffler work Wilhelm.
Advertised as running, good condition, one picture showing her from a bird view and a second picture of the tag.
Bent handle bar was not noted.

Yes, I'll run her with the SLR first so I have a before and after. ;)

I have a few small parts, a few I will have to buy, the handle bar I hope to fix.
Payed 335€ + ~20$ shipping.
It was a impulse purchase, could have been much worse.
 

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My stock 5105 and Echo CS-400 with cat mufflers are as strong as I could ever need them to be. Really, I modify my machines for reliability and long life more than anything else. I am thinking about going to non-cat mufflers on them because I don't like having that big heat sink right next to the cylinder. It seems to me like that would increase the chances of seizure and just lead to shorter life in general. I ordered the non-cat 5100 muffler from Jack's Small Engines, it should arrive at any time. I also have an adjustable carb for it, my 5105 came with the adjustments glued in place. Don't know if I'm going to do anything with the Echo or not, I've already made the carb fully adjustable and richened it some. I think Echo has been using cat mufflers longer than most and I've never read of them causing any engine failures.
 

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My stock 5105 and Echo CS-400 with cat mufflers are as strong as I could ever need them to be. Really, I modify my machines for reliability and long life more than anything else. I am thinking about going to non-cat mufflers on them because I don't like having that big heat sink right next to the cylinder. It seems to me like that would increase the chances of seizure and just lead to shorter life in general. I ordered the non-cat 5100 muffler from Jack's Small Engines, it should arrive at any time. I also have an adjustable carb for it, my 5105 came with the adjustments glued in place. Don't know if I'm going to do anything with the Echo or not, I've already made the carb fully adjustable and richened it some. I think Echo has been using cat mufflers longer than most and I've never read of them causing any engine failures.
I pop the cat out on a new ps 420 even before I start it if its my own demo/user saw or one thats out of the warrantee if asked to do so. Same reason as you with heat ...But... have to say there are plenty running just fine with the cat in place.
My 5105 has had a cat del from its muffler to keep the stock UK saw look ..I like the stock look with mods i do. We only get fully adjustable carbs on the Euro machines so never a bother to re tune.
This thing with the 7910 is a little different as its not a cat so i will only get in the muffler if it seems to have a performance + and not just use more fuel to make more noise :D
 
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FergusonTO35

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Thanks. My 5105 uses a Zama C1Q-DM13B. As mentioned before mine has the adjustments glued in place so I ordered up one that is adjustable but with the smog limiters. What's funny is, the limiters are there but they don't do a darn thing, you can go as rich or lean as you want to. I figger I'll set the high speed around 400 rpm under the factory max and call it good.
 

Simondo

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Thanks. My 5105 uses a Zama C1Q-DM13B. As mentioned before mine has the adjustments glued in place so I ordered up one that is adjustable but with the smog limiters. What's funny is, the limiters are there but they don't do a darn thing, you can go as rich or lean as you want to. I figger I'll set the high speed around 400 rpm under the factory max and call it good.
Have you ordered a C1Q-DM 20 carb ? if so then its the one we get over here. This any use to you ?
Screen Shot 2017-07-21 at 12.00.54.png
....you need to start with Standard settings with these Zama carbs when your dealing with the coil limiter. It can fool you with the top end giving you a leaner delivery than you think.
 
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FergusonTO35

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Thanks alot. No, the C1Q-DM13B is still what ours get, however they now have conventional screw slots and limiter caps. The starting high-low settings are the same, I would guess the adjustment screws are the only difference.

Fortunately, the factory carb on mine seems to be set right or pretty close to it. She starts easily and the plug has a nice coffee brown color to it. I'll put it on the tach to make sure, then cut some logs to see how it does in stock form. So far I've only done a little trimming with it, too friggin' hot here to give it a real workout!
 
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