Vintage Karting Forum

I picked up a couple of HR40a carbs.  They look like they are snowmobile carbs.  Does anyone have any information on these?

Smokey

(09-17-2018, 01:22 AM)Blaine Young Wrote: [ -> ]I picked up a couple of HR40a carbs.  They look like they are snowmobile carbs.  Does anyone have any information on these?

Smokey

The ID site I use lists them as being built for Bombardier (Ski-Do) snowmobiles.

This is a list of all the HD's and HR's and which snowmobiles they can be found on. . Some have recirculators, some have external pulse, different bore size, etc All listed

http://www.vintagesnow.com/Carburetors_f...20desc.pdf

I guess the "recirculator" feature continuously pumps fuel back to the tank. I can see why that would be very helpful in machines operating at high temperatures, (e.g., cars idling with the AC running) but why on snowmobiles?

I recall that the Walbro WDA snowmobile carbs (close cousins to the BDC-16) also had recirculator circuitry.

I searched the web for some info on this: It seems that the volatility of winter fuel formulations are susceptible to vapor lock in a hot engine compartment and recirculation of the fuel is intended to mitigate that.

I've built about 20 of those old HR's from the snowmoble era's for alky kart use. the only ones that end up being a problem is the Ski Doo ones that have the fixed/replacable jets instead of the adjustable high speed. some of that other circuitry I've identified as not necessary. When I shut that off, I tap that circuit and install a setscrew to block the passage.

Steve W wrote, "Some of that other circuitry I've identified as not necessary. When I shut that off, I tap that circuit and install a setscrew to block the passage. "

Interesting.  I recall a similar finding when I looked at a BDC-16 in some depth a few years ago.  (Cavities within that serious-looking four-plate pump stack weren't connected to anything.  I figured they were left over from some other application; probably recirculator.)

What were the reason(s) to block off the unused passages? Just curious.

some of those passages go to the high speed nozzle area or pass across the other needle areas and are not necessary. you probably wouldn't understand unless you have 6 different kind of drillings in front of you in body castings. It only takes the normal passages that really are not that different from an HL to make an HR work. Those Snowmobile carbs had all types on primer systems for cold weather etc that we don't need.