Billetron Carbs on Vtwin 250?

The Billetron Carbs seem to be the bees knees on all the 2T bikes these days. I know the TMX38 was good 20 years ago but seems rather dated now.

Does anyone in here have experience switching to a modern Lectron carb? Seems like a no brainer to me, far less hastling with jets and nozzles. Plus, many riders report significant torque/power/response improvements all across the rev range.

 

Looking for a guinea pig now, I'll let u know when we try it.
The Honda's may be a problem (NSR), as it runs the oil pump off the carbs and they're side-by-side w/no room between.
The number of 'bad' or 'something is just fucked up??' ...25+ year old carbs we get here, is a pita and a HUGE time waster.

 

Thanks. I'm actually looking at the SmartCarb SC2 as another option because they offer a 40mm option that can also take a Throttle position sensor which would be awesome for data logging. I've contacted SmartCarb and they are giving me some help along the way to get this setup working.

 

I didn't know the NSRs/RS ran oil pumps. I thought they were all premix.

 

All street based 250 v-twins are premix

 

Smart carbs are tall, you'll need extra room under the carb for the float bowl. Tried to use one an an RS125 and it just wouldn't physically fit. I loved my billet SC on my WR250Z while it was a 265 (+2mm) build. Bike might as well have been fuel injected, stupid consistent performance, easy starts hot or cold, and would idle for hours. If it's behavior changed I knew to start poking around 'cause something was up with the motor. The only 'fault' was in wet conditions the slide would get a little sticky and like to hang open occasionally. I'd prefer a stiffer return spring personally.

Now that the motor is a +6mm build, 292cc I'll be fucked if I can get it to behave with the same carb. Runs great till I go to rag it out in 4th or higher, starts pinging and will act like I've cut the ignition if I persist in holding the throttle. I've chased fuel supply, needle and seat to get more flow there, main needle to fatten the jetting, can't clean it up. I just recently backed the ignition timing off 2 degrees to see if that helps, at this point I'm getting ready to just pull the motor and rebuild it as a stock bore now that I may have a salvageable cylinder. Issue acts like it's going lean, but I'm not certain it's the carb at this point and don't have any places to test so the bike just sits now.

 

The TZ 250 airboxes are pretty large on the 5ke. There should be enough room. According to diagrams, the SC is about 10mm taller than the Mikunis

 

i have two 38mm smartcarbs for my vdue, if i could ever get the exhausts finished already i'd let you know.

 

Are you using the same pipes as on the stock/+2mm build?

 

Yeah, FMF Fatty with a ProCircuit 304 muffler.

 

I'm not an expert by any means, but with the larger displacement, I would think the pipes need to be designed for the revised parameters. It all works as a system, and changing one parameter may require other changes to accomodate things.

 

I'm sure the pipe isn't perfectly matched, but I'd expect it's impact to be more consistent. 1st through 3rd wouldn't pull my arms off, and when the bike pings, bucks, shuts down in higher gears, closing then reopening the throttle wouldn't bring it back for a bit. That behavior quirk is why I've been chasing fuel delivery for the most part. I suppose that could be the result of the pipe cooling off?

 

Leak down test and an accurate measurement of timing/ consistency of spark are the easiest things to check and first I do when there's any misfire or lack of power across the gears. When it's loke you said in top gears and other high fuel flow scenarios is when the carb, carb float level, petcock, fuel lines etc are likely.
Pipe generally just moves power around for me unless it's horribly mismatched.
Two stroke gremlins are SOBs to run down cause there are so many variables.
Both those carbs are works of art to see and handle. They make normal Mikunis and Keihins look like Webers or Amals.

 

My other theory - That big ol Wossner 74mm piston is heavier than the OEM 68mm piston, and maybe the extra vibration is frothing the fuel or interfering with bowl filling?

 

I have a Billetron 38 on my new Beta 300 2 stroke, it has ran pretty decent so far.

I've put about 30 hours on it.

Fuel economy is a lot better with it as well.

 

I should try a pair of their Aprilia RS125 models on my RS250 maybe. I submitted a tech request on their site

 

Boring a cylinder that much lowers port heights a lot and it takes some skills to adjust them. You can compare port top to cylinder top on both cylinders. Pockets in the side of the new different piston sometimes cause short circuiting between exhaust and B transfer ports next to them. If those are good and the head matches the piston, compressions right it should run

 

I really do think EFI will be huge on a road race bike. My new EFI TM300 is amazing. Its a very simple system, TBI setup with injector at the throttle bodies just like any other 4t sport bike. Maybe after I get my super single project going on the Carb, I can attempt an EFI retro fit using a DIYautotune Microsquirt or Megasquirt. That system should be able to control an ignition system, drive any servo driven powervalves, as well as control an oil injection system. Then you have all the data you need and could use it real time. I know the setup isn't as simple as a carb, but my guess is, when setup well, you would see engine service intervals and HP go up.

 

Well I took the plunge on some 38mm SC2s. Fitment is tight (float bowl is snug to the bottom of the airbox) but it slips right in with no adjustments for upper cylinder. I need to make a custom brass adapter for the throttle cable adjuster. Cutting some threads onto a 6mm brass tube should work perfect.