new carburetor

it could be a plunger like the Bing carbs have. you push it down and it pushes down on the float and that lets more gas in so you can kickstart the engine with richer carburetion, an alternative to a choke.

APT SmartCarb
25mm $450
www.powerapt.com

High Atomization
The extremely fine fuel atomization provided by the SmartCarb exceeds that of Electronic Fuel Injection, which is a result of the SmartCarb's proprietary venturi shape and features that are designed to accelerate airflow past a precision flat-ground fuel metering rod. This highly accelerated airflow results in a strong signal to the metering rod which produces fuel droplets that are much smaller and more highly atomized than the fuel droplets produced by modern EFI systems and other conventional carburetors.

Ultra fine atomization means a more complete and significantly cleaner combustion burn, resulting in lowered emissions, greater fuel economy and increased power. By effectively atomizing the fuel prior to combustion, more of the fuel is consumed during the combustion process. In addition, smaller fuel droplets mean more of the fuel's potential energy is released during combustion, leading to an increase in power. Extensive testing utilizing dozens of engines has yielded a minimum power increase of 5% and as much as 14%.

Easy Adjustability on the Go
SmartCarbs are highly, yet easily adjustable via the mixture adjuster on top of the carburetor and the idle adjuster on the side. Both adjusters are readily accessible by hand without having to remove the carburetor from the engine or even getting off the bike. Making mixture adjustments is as simple as turning the engine off, opening the throttle all the way and pushing in and twisting the adjuster to make fine mixture adjustments. And because the SmartCarb compensates for ambient air density, once the right mixture adjustment setting is found, you can leave it alone and the SmartCarb will do the rest, regardless of altitude or air temperature. No more messing around with jets!

This is another possibility:

Do you guys have any opinion on the Walbro Stage3 carbs?

It's hard to regulate a vapor carb which is why there are no factories making them.
Walbro is good but requires some DIY to install them.

jaguar said:

It's hard to regulate a vapor carb which is why there are no factories making them.
Walbro is good but requires some DIY to install them.

Click to expand...

It is worth a try for us DIYers.

After all, most of us don't buy our bikes ready made.

Jag what do you think of this? https://thunderproducts.com/product/u-f-o-ultimate-flow-optimizer/

very interesting.
but at full throttle the slide is all the way out of the flow path, unlike their drawing, and so I think this product would have zero effect at full throttle. Possibly at lesser throttle positions there may be better atomization which would give better power when slowly cranking the throttle open when accelerating. I think it would require leaner jetting from the needle which is hard to do on all carburetors. Maybe some company should make their own carburetors incorporating this idea, with their own jets.

Here's what was said on the "Cafe Husky" forum by a guy with a single cylinder 430occ Husqvarna MX bike.
As I predicted the needle jetting had to be leaner. This guy did it by drilling a hole in the shroud that sticks up into the flow path in front of the needle jet opening which relieves the vacuum at the jet, therefore making it leaner.

"I spoke with Lonn (designer) He advises that the 1.5 - 2 hp per 100cc is based on multicarb, multicylinder 2 strokes (Snowmobiles with greater port swept area). A 70-80's single cylinder 2 stroke can expect .75 -1 HP per 100cc after jetting changes. Almost all increase is in low to mid range. Most comments reflect the perception of instant throttle response and bottom end drive. He suggested that the "Dial-a-jet" is a good companion as it targets top end performance."
"I took it for a ride after a short warm up and noted that there is indeed a crispness in throttle response that was not there before, but it is too early to say if is worth it yet."
"The last reported pilot jet was one that had been soldered closed. It too proved to be too rich after full warm up. The next step in the installation guide is to drill an air bleed hole in the needle jet hood [which would lessen the vacuum on the needle jet]. So… because I was less than confident this would be race worthy on July 19, I went to Cycle Gear and ordered a new Q-8 needle jet from Parts Unlimited in case I need to go back to the original jetting. I then used a #55 drill to place the air bleed hole as directed on my current Q-8. I was very close at this point but a little lean. I reinstalled the #15 pilot jet and it’s back to too rich. Drill out the air bleed in steps #52, #50, #47 testing each time with the #15 pilot jet. I am now about right and I have a functioning airscrew for air density adjustments at the track.
Performance testing on the street or just ****ing off the neighborhood?
The claim is more low-end and mid-range performance, with .75 to 1.0 HP increases per 100cc of displacement. I can say with certainty that it sharpens throttle response. My feel is that the performance increase is throttle position sensitive in the low/mid RPM range. I can feel a difference in roll-ons and part throttle operation, but at full throttle it is about the same as before. This makes it better suited for off road use (IMHO) because Mxer’s tend to spend their time at one of the two extreme positions (On or Off) Still, may be of use on those sweepers.
A shared thought here on the limits of perception, I recently changed the porting on my 430 with the result of more felt low-end power and a big mid-range hit that was not there before. As a result, I cannot honestly say there is an improvement once I make it to the mid-range hit because if it is there, it gets lost in the crowd.
I hope to make it to the track on Sunday for some final testing and assessment.
Is it worth it?
I am going to say yes subject to further evaluation at the track. I am done or near so and there is a performance improvement. $30.00 does not seem like much to pay for ponies these days and I enjoy a personal project.
BUT… This is not a mod for the beginner. I spent at least 8 hours on this. I lost count of the times I removed, modified, installed and tested the carb. It is not “Plug and Play” by any estimate. I have a lot of experience and a machine shop at my disposal. Let the uninitiated beware.
I did at last make it to the track on Sunday. I had left the fuel tap on from the night before and when I got to the track the bike was very flooded. After a lot of cranking and pushing, it finally started and I was able to blow it out. I didn't think to do anything else but ride and began to make 5-6 lap sessions. After a few sessions I checked the plug (old) and it looked good but slightly lighter than before. I felt the bike was hard to hot start and tried a couple richer pilot jets. That was the ticket. With a #25 pilot the bike would start on the 1st or 2nd kick both hot and warm. I should note here that means I overshot the sizing on the air bleed hole. So if I had a "do over" I would stop at the #55 drill hole and head to the track for final setup.
As for perceived performance improvement on the track. It is difficult to tell. Big hits felt on the pavement vanish into wheel spin in the dirt and small improvements?...I think I can feel a bit more just as I open the throttle.
I'll say again, A lot of work and technical savvy required for installation and setup.