Progressive Modding of a Dolmar 7900

[blsnelling]

At the risk of failing publically, I'm going to show the progression of events as I mod this Dolmar 7900 with the HD filter setup. I'll tell you right up front, this is the first 7900 I've modded. The 7900BB prototype I demod was left stock except for a muffler mod. If I screw it up, I'll put a new topend on it and be done with it. However, I've yet to see a saw that didn't respond to a little port and muffler work. With that disclaimer out of the way, here we go.

To start off, I heat cycled the saw a couple times, allowing it to cool off after only getting it good and warm. No cutting or WOT. I then cut 2-3 cookies and let it cool again. I've now trimmed the H limiter cap and tuned it in an Ash log.

This first video is a bone stock saw with the exception of trimming the limiter stops.

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[FELLNORTH]

I'D REP YA BUT IT WONT LET ME....
THANX FOR VIDS... ALWAYS A PLEASURE.
I LOOK FORWARD TO SEE THE PROGRESSION

 

[blsnelling]

I'll mod the muffler next and get some more vids. Then I'll finally go in and do the port work for the final mods.

 

[fredmc]

Are you gonna share the port mapping and such? I've yet to touch mine other than the matching, MM and an .019 squish I did. In fact my 7901 fells trees better than any other saw I've used at that weight modded or not. It bores well, limbs, bucks and noodles like a raped chimp on meth.

 

[TRI955]

opcorn:

 

[blsnelling]

Are you gonna share the port mapping and such?

I'll share any info or anything I learn along the way.

 

[fredmc]

I'll share any info or anything I learn along the way.

Far out!

 

[blsnelling]

Far out!

No reason to change now. No secrets here.

 

[nmurph]

are you going with the unlimited coil and re-keying the flywheel???

 

[blsnelling]

are you going with the unlimited coil and re-keying the flywheel???

No. As much as I'd love to not have a limited coil, I'm not a fan of a keyless flywheel. Especially on a customers worksaw.

 

[roncoinc]

blsnelling Progressive Modding of a Dolmar 7900

--------------------------------------------------------------------------------
At the risk of failing publically,

After what i have read the last year,,have you ever failed at ALL ??

now tell me how to port my ryobi !!

 

[Andyshine77]

My ported 7900 has three 1/2" holes in the front of the muffler. Don't remove the baffle cage in the muffler, you can open it up a little, but it's not really necessary. Don't go bigger than whatever the volume of 3 1/2' holes comes out to, if you go bigger you'll lose power.

 

[angelo c]

My ported 7900 has three 1/2" holes in the front of the muffler. Don't remove the baffle cage in the muffler, you can open it up a little, but it's not really necessary. Don't go bigger than whatever the volume of 3 1/2' holes comes out to, if you go bigger you'll lose power.

Andy,
How did you go about opening up the muff ? any Pics ?
A

 

[MCW]

I watched a really good girly video on the internet last night (OK, maybe not) but have a feeling that the progressive mod videos on this saw will be far more entertaining. That looks like pretty hard wood too?
Brad, I hope you don't have to wear earplugs and earmuffs after any muffler mods?

 

[Andyshine77]

Andy,
How did you go about opening up the muff ? any Pics ?
A

I didn't open up the muffler myself, the saws builder did. It's simple but effective, some people like it some don't.

Sorry about the image quality.

 

[Tree Sling'r]

Strictly porting Brad, or are you getting some machine work done?

 

[angelo c]

Thanks Andy,
any spark arrestor or is it "free balling"...

 

[blsnelling]

Strictly porting Brad, or are you getting some machine work done?

No machine work planned.

 

[blsnelling]

My ported 7900 has three 1/2" holes in the front of the muffler. Don't remove the baffle cage in the muffler, you can open it up a little, but it's not really necessary. Don't go bigger than whatever the volume of 3 1/2' holes comes out to, if you go bigger you'll lose power.

Now you tell me, lol. Looks like I proved your point. I gutted the internal cage. I then opened up the factory exit and replaced the screen. I also added a second port and used a Husky deflector. It could be that it's not tuned perfectly. Back to the drawing board.

It sure sounds good

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[MCW]

Excellent job mate, nice work.
Looks like there may have been a bit of supercharging going on too with the wind in the background