My build/restoration plans,,,,,

1. '84 250 WR AC stock. UFO mod.
2. '83 430cr modified, flat side carb, small rotor, ported per factory specs.
3. 80 390/420 OR 40mm carb ported factory specs. UFO mod.
4. 79 250cr stock. UFO mod
5. 82 430xc, motocross suspension. UFO mod
6. 500cr future plans

That's my Husqvarna museum tribute.

What is an UFO mod? Does that mean UFO aftermarket plastic parts?
As to #3 a 40mm carb on that reed cage and transfer ports seems a mis match.

I built a 390 cr with a 40mm carb already only for a experienced rider. With the UFO, needle jet changed.

The UFO is a plastic round wedge that goes under the round slide carbs. It smooths out the gas transfer. It's very popular on the snowmobiles. Works awesome on the round slide carbs too.

http://thunderproducts.com

Ultimate Flow Optimizer

My '81 Husqvarna 250cr ported, advanced static timing, reed box spacer, UFO installed was a screamer. This bike flew. With the UFO also comes rejecting. The pilot jet in this bike was #35, it's a 250 with awesome throttle response.

After installing the UFO, I file and sand it to fit the round slide perfectly.

After talking with folks about the new Lectron carb. I would only consider their carb for what you are talking
about Bill with your 40mm. You will find these set up like Dicks racing does , with a 38 taper bore that expands
to larger bore. They also have mods you can do to even increase the bell housing flow.

I have heard time and time again not to install the flat side mikuni carb on the 430 from other husky engine builders , they
say for some reason jetting, flow etc, just working right here for 430 for some reason. I wanted to do it - all others said no don't.

Remember guys here on site modified there 500s and went back and installed a 38mm - and write up is also in the husky newsletters about that mode. An injury stopped his riding bikes but did talk to him on phone in last year and he loved the overall lower end
powerband and starting improvements with a 38mm on his 500.

I got the 40mm jetted correctly on the 390. I ordered the smaller needle jet from Pro-Flo out west. He was surprised that I was doing this. He races Daytona during bike week. He uses two 40mm carbs rejetted to his twin cylinder race bike. He's done the same thing I was trying out. He has won many races using the rejetted 40mm carbs. The 40mm carb on a 390 isn't for the faint hearted. Word of caution. Do at your own risk.

If your thinking about doing one little change with the stock 38mm carb the UFO is what I would suggest then reject it properly.

TM/TMX flat slide Mikuni's dont work well on any bike, which is why very few came with them, the stock round slide is much better. If you are going to go to the trouble of replacing the stock VM38 you should go all the way and get a Lectron.

As for the 40mm on a 390, its unlikely your "seat of the pants" are backed up by real numbers because the stock 38mm already flows more than the stock reed cage can flow, so going to a 40mm will only reduce low/mid range and add nothing to the top. What it will do is reduce the midrange and give it more "hit" so its FEELS faster, but it is in fact slower. Feeling faster does not equal being faster.

the 38mm does run much better on the 500s..i can imagine it being over carbed on smaller bikes..
the factory taper boring on the lectrons look fantastic. i would never spend money on band-aids let alone another carb over one.

I did install the UFO in the 40 mm.

At what years do the Lectron carbs become AHRMA legal? I know they are not allowed on vintage bikes.

It is my understanding that Lectron is allowed and is only square slide allowed because it was offered and sold in the 1970s as an option. I had one for all of 1978 season for my 390

Now my question is is their a problem of allowing the new version with adjustable main jet ?? Note - we believe several of us that the rules state that no electrical power valve
is allowed. Powerjet powervalve ? hmmm ?

They are legal for all PV classes, so roughly '75-up.

The powerjet is passive vacuum operated and is legal, you can also add one to a Mikuni using a Mikuni kit.