Other How to tell SBN 44 from 46?

[Cannibal]

Alright, so I have what I thought was a Blackjack 44 sitting here and what I thought are a pair of aftermarket 46s in front of me. The bottom of the Blackjack is 45.12mm and look to have the factory finish. The machining where the butterfly is is a little bit narrower and is pretty much true all the way up to the collar that Art presses in.

The "46s" are 45.11mm on the bottom and step a bit narrower as well, then even narrower for the bomb site area.

Both butterflies on the BJ and "46" are marked with a square with 120 next to it (if that means anything). The butterflies look identical in size, but I can't get in there to measure, but the "step" to the butterfly area feels the same on both carbs. Pretty sure whatever I have are the same carbs, I just don't know the same what?

The bolt pattern on the bottom is the same on both carbs, about 76mm center to center if that matters.

Seems like such a dumb question, but I "assumed" my BJ was a 44 (it came on a SN I had way back). So of course it through up a flag when the 46s I bought were the same size.

Thanks!
Steve

 

[SUPERTUNE]

If you look from the bottom of the carb, the 44mm carb will have a cast in step about 7/8 inch deep, 46mm carbs the cast step will be about 7/16 inch deep.
If you look at a 44 and 46 side by side, the less step will be the 46mm.

 

[Cannibal]

Hmm, that step is the same on both carbs, at about 11/16" with my ruler.


I should also add, the top opening on the "46s" are 46.46mm.

Kinda wish I had some stock 44s here to compare them to.

 

[Cannibal]

Here's a pic. BJ "44" on left "46" on right.

The bottoms are identical. So I either have a BJ 46 or a pair of aftermarket 44s.

 

[snowxr]

The 46's I have all have a wider bolt spacing where they meet the manifold. It looks like you have 44's.

 

[ajmps1]

doesnt art remove the venture? just smooth taper bore all the way? so does the "bj" have a full, partial, or no venturie?

 

[Cannibal]

Ya, BJ has no venturi at all. Comparing the two (that seem identical), you can see where the "aftermarket" machining is. Art basically machines out the venturi and presses in a manufactured annular discharge throat. These two carbs seem identical. I'm thinking I bought some 44mm carbs that were advertised as 46s. The price was great for 46s, but only good for 44s. I surely don't want to make this claim unless I'm sure of what carbs I actually have here in front of me.


snowxr, that's what I'm thinking. I'm hoping someone can provide me with some numbers so I can compare. I don't want to make false claims against the seller. I want to be 100% sure.

 

[ajmps1]

your using calipers, was the "with my ruler" just a saying? you should contact the seller about it, was it fleabay?

 

[Cannibal]

Can't get a set of calipers up there, at least not my calipers. So, ya, it was a ruler to measure up into the bore from the bottom to that machined step where the butterfly seats. I actually measured the top and bottom bores with a caliper.

I did find a site that spelled out that the top opening of 46s will be 48mm. These top openings are only 46. I took a metric tape measure and opened the butterflies and found they are 44mm butterflies (actually closer to 44.5mm)

The seller is on here and I have contacted him. He maintains that these are 46mm carbs.

I have a feeling I'll be sending these out for 3rd party evaluation. Everything I find point to the fact that these are 44s, but I hope I can get more tech info to make 100% sure.



Dumb question for anyone, but do 44mm carbs have a 44mm butterfly? and 46mm carbs have a 46mm butterfly? I have assumed this was true, I've never actually measured anything before.

 

[Cannibal]

I actually hope these turn out to be 46s. I already bought a big pin manifold to use the Rhaas Speed Plate system and some air filter adapters.

 

[Cannibal]

Just got off the phone with Mikuni. I gave him the stamping of Mac 52 and he confirmed that it was infact a 44. I also gave him the stamping on my BJ (Mac 67) and he confirmed it a 44 as well.

 

[ajmps1]

that sucks

 

[Cannibal]

Ya, it does.

I'm pretty confident the seller didn't knowingly sell me 44s.

Good thing is that I can just use my BlackJacked SXR I bodies until I find something better.