• Husqvarna Motorcycles Made In Sweden - About 1988 and older

  • Hi everyone,

    As you all know, Coffee (Dean) passed away a couple of years ago. I am Dean's ex-wife's husband and happen to have spent my career in tech. Over the years, I occasionally helped Dean with various tech issues.

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40mm flat side carb

Big bill you are going down the wrong hill again the 38 carb has improved even the 500 for powerband see write up in the husky newsletters and the feedback from the folks who installed
them on there 500s.

Heres why the 38mm has a higher velocity and even flow as compared to the 40s. The 40mm can't suck as much fuel. The 38 can push/ pull mixture faster and more even flow also.

Also you have to look at case volume, the 390, 430, 500 lower case volume really does not call out for a 40. Friend has even added the boost tunnel ports behind sleeve from intake to lower transfer( its a true tunnel ) like the 84 250WR on his 490 Maico to increase lower end volume flow. A 38mm can easily handles this larger volume. He only tapers carb at end. (Note - Snowmobile race folks do these tunnel ports)

A taper bore may work a bit, but the intake on the husky really could not take the additional flow without doing the Factory upgrade with the window ports to piston and eyelets to intake to match.

Please note husky went to a 38mm on the 500 in later years models. A 40mm is waste of time on the 430 and the 390. Ok just consider a tuba , or a trumpet. the big one or smaller one. Which flows the air faster like a race engine needs. That 40 is just like a big tuba.

Please note having a complete software Analysis done for fun and interest on the port timing, lower end volume. head volume, on a 430 and 250 cylinders with the a guy who wrote the software. Should be interesting. coming later in Sept. after he comes back from vacation.
 
A stock 38mm Mikuni round slide will flow more than any 430 so "improving" flow is irrelevant. In addition, as GaryM notes, you will be losing the ability to control the fuel because of a weaker vacuum signal. This is just the down side of going to a 40mm round slide, not even taking in consideration the additional faults with the performance of the TM/TMX flat slides compared to the VM round slide.

And just to reinforce the point, both the KX500 and CR500, both bikes that make significantly more power than even the Husky 500, run 38mm carbs.
 
Kartwheel68 said:
A stock 38mm Mikuni round slide will flow more than any 430 so "improving" flow is irrelevant. In addition, as GaryM notes, you will be losing the ability to control the fuel because of a weaker vacuum signal. This is just the down side of going to a 40mm round slide, not even taking in consideration the additional faults with the performance of the TM/TMX flat slides compared to the VM round slide.

And just to reinforce the point, both the KX500 and CR500, both bikes that make significantly more power than even the Husky 500, run 38mm carbs.
Click to expand...



not so sure they make more power but they also use a 39mm
 
When I ordered the mikuni parts for my 40mm round slide the guy in CA. Told me he thought he was the only one in the country doing this. He raced T500 Suzuki at Daytona using twin 40mm carbs. He was winning his class. I ordered a few different sizes of the needles and needle jets. I dialed the 40mm carb right in on the 390cr. The bike was sold twice and still ran. This was almost 2 decades ago. The bike was a lot to handle but it was fun.
 
Bigbill said:
When I ordered the mikuni parts for my 40mm round slide the guy in CA. Told me he thought he was the only one in the country doing this. He raced T500 Suzuki at Daytona using twin 40mm carbs. He was winning his class. I ordered a few different sizes of the needles and needle jets. I dialed the 40mm carb right in on the 390cr. The bike was sold twice and still ran. This was almost 2 decades ago. The bike was a lot to handle but it was fun.
Click to expand...
losing bottom end power isnt all that much fun. switching my 500 over to a 38 was the best thing i ever did to it. i dont run it at daytona either.
 
Bigbill said:
When I ordered the mikuni parts for my 40mm round slide the guy in CA. Told me he thought he was the only one in the country doing this. He raced T500 Suzuki at Daytona using twin 40mm carbs. He was winning his class. I ordered a few different sizes of the needles and needle jets. I dialed the 40mm carb right in on the 390cr. The bike was sold twice and still ran. This was almost 2 decades ago. The bike was a lot to handle but it was fun.
Click to expand...

Are you building a road racer or a dirt bike? This is a lot like your porting advice from the chainsaw racer, just because it is good for them does not mean you should do it to a dirt bike. If you are not building a road racer then the comparison to a Suzuki 500 twin is not only irrelevant, it will result in a bike totally unsuitable to being ridden in the dirt.
 
just pick up a lectron already for one of your huskies if you want a new/fun experience. you will love it..the externally adjustable powerjet is tits!
 
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