2511 Build

[2000ssm6]

I'd be interested to see what yours makes also.

I haven't ran all the small rear handles but love the 200, they work great for my dad in his 70's also as he can't start the larger saws.

 

[Nutball]

Okay so not even work on them at all? I have them measured up. Secondary up .025, and primary a few degrees past that. Basically putting the secondary back where it is stock and the primary increased just past that, I'm deleting the gasket only.

View attachment 355615

I might tweak them ever so slightly especially at the cylinder wall, but I've gotten good results and feedback from leaving them alone. I could be leaving power on the table, maybe not, and maybe my recipe works best with minimal upper transfer work. The most I've ever done to the uppers was quite insignificant if memory serves me correctly.

I just looked at a picture, and I actually do change their timing, but hardly their shape: I make a popup piston.

 

[Ketchup]

Okay so not even work on them at all? I have them measured up. Secondary up .025, and primary a few degrees past that. Basically putting the secondary back where it is stock and the primary increased just past that, I'm deleting the gasket only.

View attachment 355615

I would raise the primaries and leave the secondaries.

 

[Crocky28]

For me, larger intake numbers weren’t getting the power your saw has in the video. Slower to rev, and generally a lower RPM in the cut. I went that direction hoping to get more power behind a 14” bar, but it just wasn’t working. The first 10 or so saws I left the intake at 71-72, then progressed down to 76 with the next 4 or 5. They all ran great, but when I brought the intake back above 70, I instantly felt they were stronger. I made other changes along the way, so there’s a lot of variables.

With the intake high I can raise the transfers a bit more. The saws rev super fast. Honestly, your video is very similar. A nice high power band in the cut.

Bare in mind that I’m working from 5,000-10,000’ (roughly 1,500-3,000 Meters). Saws want to run rich here. It may be that extra intake would be better at lower elevation.
I’m also keeping the transfer tunnels pretty tight. Larger case volume might want more intake duration. Though just the volume of that one stuffer doesn’t seem like much.

Your saw sounds great. Have you tried it with a 14”?

Yeah it runs really well with a 14”. It’ll out cut a stock CS362 with 14” 1/4 on. I have 20” bar there to try just for fun. I think it’ll pull it no probs.

I might mess about with the carb as I’d like more fuel top end.


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[Ketchup]

Yeah it runs really well with a 14”. It’ll out cut a stock CS362 with 14” 1/4 on. I have 20” bar there to try just for fun. I think it’ll pull it no probs.

I might mess about with the carb as I’d like more fuel top end.


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So the carb…

Initially I thought the carb needed some work to help a 2511 but as I ported more of them I found they were pretty good stock and messing with them didn’t show real gains. I’ve run across a few ported 2511s by other folks with modded carbs, even swapped a few onto my own saws. Again I felt they gained little and usually made tuning more difficult.

But really, I hadn’t deeply explored carb mods for this saw. A couple months ago I started looking into it a bit deeper. I found this scooter discussion very helpful:

https://www.billetboard.com/forum/scooters-gas/scooter-engine-tech-talk/9324-

There were a couple big take-aways for me. First, the WT family is very large. Second, the body and circuitry is the same in almost all models (some WT carbs don’t have a choke, such as wt-194, most don’t have a primer spigot). Third, Walbro was kind enough to mark the venturi size on the body. So there is a lot of opportunity to take a larger carb in the family and cobble together a bigger carb for 2511. Based on the above discussion, I tried to hunt down a larger venturi WT carb. Perhaps foolishly, I bought an AM WT 591 to tinker with. Saws are just a hobby, so it sat in a box for a long time.

A few months ago, I pulled a carb off a cs-490, and immediately saw it was almost a direct swap onto a 2511.

For some reason I decided to mess with it today. Wu Tang 591 on top, stock WT 1208 on bottom.


I was pretty disappointed to discover that my knockoff 591 has the same venturi size as the 1208 (11.15mm). I think this is the asian manufacturing. An OEM 591 should have a much larger venturi. There is a NOS 591 on Ebay, but my experimentation budget is a bit slim right now.

Anyway, I figured since the throttle bore was a lot bigger, I’d give it a try.


I swapped the choke shaft, butterfly, throttle shaft linkage and the internals that I thought were suspect on the 591. I had to drill a new locate hole for the throttle shaft spring and clock the fuel inlet spigot.

There were a few more things that made me regret the AM 591. The Venturi was rough and needed touched up. The jets are rudimentary compared to the 1208. The lever spring was almost 2mm longer.

I guess it’s worth a try.

 

[Ketchup]

I also pulled the 490 down and yanked that carb (WT 1009). I swapped the choke shaft and clocked the intake spigot. The metering plate also needs swapped and a hole drill to match the pulse on 2511. Here’s a 1208 and 1009 side by side. They’re definitely siblings. No primer outlet on the 1009.



The 1009 has a 13.49 or 13.5 mm venturi (2.35 mm larger). It also has a throttle bore larger than 1208, but smaller than the 591. Here’s all 3 pretty far along in the swapping.



I mentioned that Walbro marks the Venturi size. Lots of people probably knew that but I didn’t. It’s a number cast into the choke side of the Venturi. The number represents X/64ths. Here’s a photo of the 1009.

You can see “34” to left of the main jet in the shadow.
So 34/64= 0.53125”. Convert to mm (0.053125 x 25.4 = 13.49375mm). I checked it with calipers and got 13.47etc.

So I’ve got one carb to try with just a bigger throttle bore and suspect internals. Another with a larger venturi and throttle bore. Unfortunately all the 2511t are in the truck at the yard, 25 miles away. Could be a few days before I can test.

 

[Ketchup]

Of course, the big question is the jets. I don’t know the sizes on any of these carbs. I’m guessing the 490 has a larger main. The 591 could be anything. That’s the next thing to mess with. Just starting into this.

 

[Crocky28]

Nice posts man! Great info. I’m excited to see how it goes. I def feel they could do with a bit more fuel top end once ported.


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[Ketchup]

Nice posts man! Great info. I’m excited to see how it goes. I def feel they could do with a bit more fuel top end once ported.


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I think that will be a jet thing. Have you tried to push out the main and enlarge the orifice? I’m leary of getting it to re-seat.

 

[Crocky28]

I’ve not done anything with the carbs yet. It’s been on my mind but not had time yet. I think my next build I’ll have a play around.


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[Ketchup]

Well, I rummaged up a third 1208 to hack, so why not try to drill the jet? It was pretty easy. It punched right out with a brass punch. Seemed to go back in tight. I just bumped it from 0.95mm to 1mm. Unfortunately, my pen drills have a gap from 1 to 1.13mm. 1.13mm seemed overly large.

One of the things I’ve never understood about WT carbs is that they have 2 circuits to the high jet. One pulls from beside the metering needle and is just a hole. Then there is another circuit that I believe pulls from the cap marked 40. I think the cap marked 34 goes to the low jets. You can see the end of the first circuit opening into the main jet bore in this photo.
Other side, pulling from the needle and 40.

They main jet has a very small hole on the metering side.

And a larger hole on the needle side. That’s the one I drilled out. I may have to drill the 40 cap as well.

Even then, the circuit bore is pretty small, so I don’t know how much more fuel can get through.
Worth a try. I’ll have a day of carb tests soon.

 

[Nutball]

You will probably have problems with lean running with a larger venturi on such a small engine, and a lack of low end torque, which is desirable in a small saw since they are so low on torque anyway.

 

[Ketchup]

You will probably have problems with lean running with a larger venturi on such a small engine, and a lack of low end torque, which is desirable in a small saw since they are so low on torque anyway.

I’ve had some luck with larger carbs at altitude, but yes a lean condition is definitely a risk. On the other side, the larger jet may be too fat for my elevation.

How is low end torque effected by a larger Venturi? Is it related to the relationship between venturi and jet, or is it simply the effect of a sluggish intake?

 

[Nutball]

Carbs are sized to flow a certain range of CFM. It is hard to cram more than a certain amount of air into the carb bore, but with a larger bore to reduce flow resistance on the same size engine, the engine won't be able to form as much low pressure past the jets causing less of a fuel draw. A similar thing happens at low rpm at full throttle, but it is amplified by a larger carb. the small engine might run great at much higher rpm than normal, but could lose its ability to draw sufficient fuel at low rpm. Great for racing, but might not run well for work.

 

[Ketchup]

I finally did some tests at @davidwyby ‘s SocialistSawfest. Thanks, @cuinrearview for humoring the experiment. Chinese carb is junk (big surprise), I couldn’t find a tune. 490 carb is way too lean. Dies as soon as you open the choke. It almost idles at 4-1/2 out on the L.

The bored jet stocker has potential. Finding the tune was a pain, but Tim ripped some cookies with it. Seemed good at first but leaned out in the cut. I think I need to bore the 40 cap to match the main.