The Dolmar 7910 - Snellerized Style

[bwalker]

Hopefully Brad will give us his time to really test the difference. If he doesn't have big enough wood, then maybe an 8-pin might substitute for an extra load.

Rich has noticed a difference between the jetting on stock and ported saws. I expect that is because the torque peak has been raised on the ported saw and the low speed circuit has a bigger gap to fill before peak torque. Rich has bridged the gap with a bit more low speed flow.

A carb swap is an easy mod for most guys. Do a muffler mod and then a carb swap and most of the EPA issues have been eliminated.

There is still the issue of excess hydrocarbon emissions that Blair refers to in his work. The factories are running around 2 degrees less blowdown to help control them. Not a biggie for most wood cutters, but a port job and extra compression (nitrogen oxides emissions) changes the picture on performance for the enthusiast.

I'm looking forward to the comparison of the stock EPA carb to the modded carb. - Brad, put some freaking load on the saw and make the saw WORK.

Two strokes have natural low NOX emmissions. This is due to the way they are scavenged and the residual exhaust gas always present in the conustion chamber. Sort of like built in EGR.

 

[blsnelling]

Why was it horrible...was it Stihl chain? Or, filed by a cull?

Yes, it was filed by a cull, lol.

 

[Tractorsaw1]

Bummer, first someone cuts up the wood & then no video [emoji35]


Sent from my iPhone using Tapatalk

 

[blsnelling]

Finally! The long awaited video. I had a chance to run the saw again last night. Since last time, I've gone back in and done more port work. It made a difference. I've also got a better chain on it this time. Even though brand new, it's running neck and neck with a well broken in EHP 7900. That makes me happy

 

[Poleman]

Nice videos Brad, and a good comparison of popular saws!!!!

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[blsnelling]

I plan to play with the carbs next.

 

[smokey7]

Absolutely perfect video that's exactly what i like to see.

 

[Jeffkrib]

So Brad whats you humble opinion on that 7910? From here it looks like you can lean on it quite heavily.
How would you rank it against a ported 461' 576 and 372 for a heavy handed user with a 28 inch bar?
Ta
Jeff

 

[David Young]

Lol. That's all I've got for now. I will tell you this, I saw 15,100 while playing with the tune

brad does the warning in your picture concern you at all?

 

[David Young]

Can someone explain why the manufactures go with limited coils? Seems to me that an unlimited coil would be cheaper to produce, easier for techs to tune, more reliable since there would be less circuits inside the coil.

Must be a reason since just about every manufacturer is switching to them

 

[David Young]

nice looking saw btw, clean looking work.

 

[blsnelling]

brad does the warning in your picture concern you at all?

Nope

 

[David Young]

I dont know why they put the warning I have never heard of anything going wrong with them. maybe the magnets get dizzy.

 

[David Young]

oh what were the stock numbers? did you stay close to the stock numbers?

 

[blsnelling]

I don't have the numbers in front of me, but they weren't changed much.

 

[David Young]

its amazing how well they run and the numbers don't make conventional sense. I don't understand why the other companies didn't try to mimic the success.

 

[blsnelling]

I'm home with Shingles while the rest of the family is at my Mom's for Thanksgiving. While I don't feel all that great, I don't feel too poorly to mess around with a saw

I had a few more mods to try on this saw and did so last night and today. I'm very pleased with the final results. I slightly altered exhaust and intake port timing. I added a much larger Walbro RWJ4 carb. I bumped the ignition timing another 2°-3°. And, I added a second port to the face of the muffler. I also used Aluminum Black to blacken the cylinder. I tried using it on the handle, but it didn't look that great, so I painted it. It's in the oven curing now. I also decided to paint the muffler. The black oxide didn't take very well on it at all.

Here's the saw in it's final configuration, before the additional cosmetic work. Yes, it's on the lean side, but quickly begins to 4-stroke in the cut and not run as well if run much richer at all. She's tuned to 14,700 after coming out of the last cut. This is a Stihl RSC chain, round filed, with the rakers set rather aggressively.


Here's the additional muffler port.

Here's the blackened cylinder.

 

[blsnelling]

Here's to show you what only 2°-3° of ignition timing difference can make! BTW, this was before the additional port in the muffler. It seemed to benefit the loaded cut the most.

+32°


+29°

 

[Poleman]

Brad, hate to hear about your Shingles...hope you get better soon.

How and what did you use to mount the RWJ carb and still use the HD filter??

 

[blsnelling]

How and what did you use to mount the RWJ carb and still use the HD filter??

All factory parts. The carb sets at an angle since the mounting holes aren't level. I had to heat and bent the throttle cable sheath holder. The biggest obstacles were limiting the travel on the fast idle arm of the choke, so that it wouldn't come back up and rest on the rubber filter boot. I actually drilled and tapped a very small hole in the side of the carb. I did the same thing to limit the over travel of the choke. After removing the baffle in the venturi, I goes past level. There are two remaining issues. In order to make the choke work at all, the arm has to be flipped up, rather than down as it comes. That means that to choke the saw, you push the choke rod in. For run, you have to pull it out. I don't like that, but I don't see any other solution with this carb. The only other thing is it idles too high and can't be adjust down. The notches in the throttle plate are much larger than on the stock carb. It's simply getting too much air. To get it any lower would require making a new throttle plate. It's idling about 3,300 right now, which isn't really an issue. It runs great in every way though. It idles great, has great throttle response, spools up quickly, and tunes easily.