SmartCarb 28mm billet carbs

[Yamavarna]

Has anyone tried these carbs? They are designed by the same guy that did Lectron carbs and are supposed to be better in every respect, they claim more power, better mileage and look like they will bolt right up and they are very nice looking!

[Yellow and Black RZ]

Look nice, simple. $550 each.

[85RZwade]

Here's a recent discussion:

http://www.2strokeworld.net/forum/index ... pic=2271.0

[Hooligan]

The price is the limiting factor when we need two of them. Maybe a larger one with a Y-boot intake would be the key.

[Yamavarna]

I read the thread from 2 stroke world and they are really just complaining about the price which is intimidating even if you take a good look at the product. I’m wondering more about the size; SmartCarb says their carbs outflow other carbs of the same size and my bike is getting a hot rods crank and I would like a set of pipes, but the carbs on it now are 26mm so: would this be like putting 30mm pwk’s on it and do you think it would still be street-able and work fine when the power valve is not open? I think I will also reach out to them keeping in mind that their opinion may be biased.

[Darrell]

Here's what Ed Toomey has to say about larger carbs:

Personally, I would like to see the smallest possible carb on your bike, not the biggest! Emotions aside, the facts are, that the stock carb can out flow the stock reed valve almost two to one, so why make the carb bigger? All that happens, when you do, is the air flow slows, and it makes it much harder to atomize the fuel droplets nearly as fine as with a high speed flow, making them harder to burn therefore contributing less to power. The net result is less power and range.

There's more to the statement here: https://websites.godaddy.com/blob/d08aa ... 7190402630

Toomey knows what he's talking about.

[Yamavarna]

Darrell, that was an excellent read but Corey Dyess from SmartCarb got back to me when I approached him with Ed Toomey’s advice and this is what he had to say:
Hi Charles,

One of the hallmarks of the SmartCarb is it's venturi shape. Much smaller at the bottom and larger at the top. As such, the tradeoff from top to bottom, or bottom to top performance is nowhere near as pronounced as conventional round slide carbs. Our 25-28mm carb float bowls carry 1.5 more cc's than the Keihin PWK.

Keeping in mind that he may be biased! I do think that these carbs with their pear shaped Venturi and superior atomization may be the ultimate answer; with some Toomey pipes and Boyeson reed valves of course! Some people on Ktmtalk are comparing them to tpi because of their superior atomization and constant pressure adjustments.
Thanks for all of the informative posts I am trying to modernize my bike in every way possible (suspension, brakes, tires, ignition and frame stiffness so I think this is a logical addition

Charlie

[brrrappp]

This is a really interesting topic. It would be fun to have an independent comparison dyno test for this carb.
The pear shape makes sense on paper but as with so many 2-stroke performance subjects, often the logical or pleasing to the brain fix is not productive. That said, the write up from Smart Carb and the pictures look really compelling. If you have the money, it would be a really fun project. I'd love to see a before/after dyno chart if you go for it.

The comparison to a stock carb will be hard to make. Most people agree that a flat slide/guillotine slide generally perform better than a round slide.

I think about all the different progressions in flow technology we have seen over the years.
Sharp edges VS round edges.
More Oil vs Less
Rough surfaces vs smooth surfaces.
Upward pointing transfers VS 90 degree transfers
Think of all the variations to the air-box shape and volume that at first seem backward to power output.

[Yamavarna]

So we’re going to do this! Corey at SmartCarb is modifying 2 28mm billet carbs for oil injection, Ed Toomey is doing a run of Rz350L pipes, Iantomasi track and trail is going to perform some porting and head work and I am going to purchase some Boyeson reeds. I’m pretty excited for this build and I build a lot of bikes, I’m hoping for mild around town manners and wild back road performance and better fuel mileage, am I asking too much? The best of both worlds? Stick around I think the SmartCarbs are going to surprise us but the proof will be in the final product. I’m also going to beef up the frame, brakes and suspension to make sure that there are no weak points in the testing. I can and will dyno test the final product against the stock carbs; if anyone wants to loan or donate some Keihin carbs we can include them and have a full blown shootout (Iantomasi has both an engine and chassis dyno) but I think the real difference will be in real world testing.

[kpke]

This sounds like a great project. I am looking forward to following along.

Have you considered VForce4 reeds?

Many here use them as does TDR in race bikes.

[Yamavarna]

Hey Ken, thanks for following along I subscribe to your YouTube channel, the Boyeson are what Ed Toomey recommended but if we are changing carbs it wouldn’t be that difficult to compare reeds also, it would just be more dyno time. I am looking for a very around town friendly bike that doesn’t care about cruising down the Main Street of small towns looking for somewhere nice to eat, in between attacking the twisty roads that connect them of course, so; the reeds flow characteristics from top to bottom would definitely come into play with this as one may be better at wfo but not so comfy putting around town and vice versa

[Smoker]

This sounds like a great project. I am looking forward to following along.

Have you considered VForce4 reeds?

Many here use them as does TDR in race bikes.

Good to know TDR uses VForce4 Reeds in his race bikes, instead of his own TDR Hyper Tension Reeds.

Makes the choice easy.

[Darrell]

Well, Charlie, it sure seems like you're doing your homework, and will do the testing. I'm looking forward to reading about your results.

I ran Lectron carbs on a TZ-500 on the race track 35 years ago, and they worked great in that application, but they sure wouldn't have on the street. Of course nothing about that bike would have worked on the street. I'm very curious to read your results on the reed test. I have Boyesons on my bike with Toomey pipes, but honestly, I rarely wring its neck and have gone to nowhere near the lengths that you're planning.

By the way, my experience with Toomey pipes included a LOT of waiting. It probably took five or six months to actually get the pipes. You may get lucky and get pipes shipped immediately, but you may have to be very patient about it. They're worth the wait, I think, but promised delivery times stretched quite a bit for me.

[kpke]

Thank you for subscribing to my YouTube channel!

When I did a complete rebuild on this engine last year, I removed the Boyesen reeds and replaced them with VForce4 reeds.

It’s impossible for me to tell the difference in the reeds specifically after a full rebuild however, although I rarely ride in town or traffic, this engine is fine putting around at any low RPM. It’s also a pleasure to redline. I think VForce4 would work in your application. You do need to modify the intake rubbers to accept them though.

[m in sc]

I read the thread from 2 stroke world and they are really just complaining about the price which is intimidating even if you take a good look at the product. I’m wondering more about the size; SmartCarb says their carbs outflow other carbs of the same size and my bike has a hot rods crank and I would like a set of pipes, but the carbs on it now are 26mm so: would this be like putting 30mm pwk’s on it and do you think it would still be street-able and work fine when the power valve is not open? I think I will also reach out to them keeping in mind that their opinion may be biased.

Not nec that we are complaining about the price and disregarding it soley on that, buts its about value for dollar. I mean, i have more in my ignition than a set of these carbs costs, so thats not the issue here.

BUT, Whats the actual gain? that seems to always be the nagging question. Especially on a street ridden bike.
A test like yours will def answer these questions and I am very much looking to seeing your results. Up to this point.. All the info we have gotten has been by sponsored users, motocross riders, or company marketing.

I do see where they are going with the pressurized fuel bowl from the intake duct above the bell-mouth, makes a LOT of sense in theory. But, ive also never even seen flow bench data on these carbs.. from anywhere. If there was an independent test anywhere, (im not aware of one until this), that thread (and a LOT of others i've read elsewhere) would probably read a lot differently.

Thanks for doing this test.

Mark