Monoblocks vs Concentrics 650SS

Personally I prefer Concentrics, have a couple of them on different bikes. Probably because I'm more familiar with tuning Concentrics. Like the smaller size and find them easy to work with. When fitted with Allen screws and the longer 622/169 extended stop screw. If they have the drain plug which I think came in 1970.
Though don't remember any problem with the Monobloc on the 99 I had in the sixties.
Only Monobloc I have now is a badly worn one on a B40WD which don't like idling when on the side stand, will soon be replaced with a new aluminum Premier Concentric. Cheaper than the Monobloc.
Slick stating "leaning a bike at speed has zero effect on fuel level in the float chambers" does not mean that fuel level in the main jet is the same on Monoblocs. Though most riders will never notice any difference. But if you are a frequent user of your knee and elbow sliders you might notice.
 
Mike40M said:
Slick stating "leaning a bike at speed has zero effect on fuel level in the float chambers" does not mean that fuel level in the main jet is the same on Monoblocs. Though most riders will never notice any difference. But if you are a frequent user of your knee and elbow sliders you might notice.
Click to expand...

The fuel level above the main jet in the right and left carbs, regardless if Monoblocs or concentrics, is EXACTLY the same when leaned at speed as when perfectly upright and stopped. A vector analysis is necessary to prove and make this clear.

The carbs float chambers are analogous to a filled glass of water on the seat back tray of an airplane in flight. When the plane is flying straight and level, the liquid surface is parallel to the surface of the earth. When the plane is banked over in a properly executed turn, the liquid surface is parallel to the aircraft's floor. In each case, the liquid surface is exactly the same distance above the bottom of the glass.

HTH

Slick
 
Slick, you are correct if the rider don't alter position on the bike. But if you alter centre of gravity of bike and rider combination by moving your body sideways it will change your force vector and affect fuel level at main jet slightly. Thus changing AF ratio a small amount. Even if you have a remote float bowl as on a Manx or G50 you won't notice loss of power when knee touches ground as you have rather small throttle openings and use throttle control to compensate. A tall obese rider on a very light bike usually don't have Monoblocs anyway.
 
Has anyone ever tried fitting TT, GP or 276 carbs with the remote or side bowls? Will they fit?
 
Last edited:
elefantrider said:
Has anyone ever tried fitting a TT or GP or 276 carbs with the remote or side bowls? Will they fit?
Click to expand...
Probably not. 276 is not flange mounted, so an adaptor is needed. But the Monobloc is an improvement. Here Monoblocs are allowed in pre -47 race class and is a good upgrade. The TT came in a lot of different sizes so it might be possible to fit if you manage to find one in decent condition. GP will fit, but you won't find any in size for a Dommie twin. Both the TT and the GP are very good at moderate to wide open throttle but are known for being very difficult to get a tickover. No problem on a race bike where many prefer to let the engine die when you release the throttle.
 
276, were they not flange mounted to the Nomad? I'd like to limit the size to no bigger than the stock 650SS Monoblock 376 size of 1 -1/16, maybe even try downsizing to 1" .
 
Last edited:
Was the balancer tube on the 650ss supposed to be brass pipe or flex rubber hose?
I have seen both.
 
Good to know, thanks. I saw this brass tube version and wondered if correct for a 650ss. Probably for an earlier bike.

Monoblocks vs Concentrics 650SS
 
Thanks, it was advertised on ebay as from a Manxman. It does look a bit "busy" to be factory stock. I was interested for the inlet sleeves as I need a pair.
 
I have seen it written where the 5/16 inlet fasteners on a 650ss should be, from left to right:
2-5/16" long studs (023563), 2" capscrew, then 2-5/16" studs again on the chopped monobloc , split washers, and reduced diameter nuts.

But I have seen it also written as taking 4 studs without the capscrew; and studs (2) on the left and capscrews (2) on the right.

So 3 different variations have been written about.

Any idea which it should be?
 
Last edited:
elefantrider said:
I have seen it written where the 5/16 inlet fasteners on a 650ss should be, from left to right:
2-5/16" long studs (023563), 2" capscrew, then 2-5/16" studs again on the chopped monobloc , split washers, and reduced diameter nuts.

But I have seen it also written as taking 4 studs without the capscrew; and studs (2) on the left and capscrews (2) on the right.

So 3 different variations have been written about.

Any idea which it should be?
Click to expand...

My Atlas, the natural descendant to the 650SS, originally had the first variation you describe.

Slick
 
Thanks Slick, is it easy to remove the carb with that long capscrew or do you think a stud/nut there would be an improvement?
 
Last edited:
elefantrider said:
Thanks Slick, is it easy to remove the carb with that long capscrew or do you think a stud/nut there would be an improvement?
Click to expand...

Piece of cake with the capscrews, especially by using a hex key long enough to extend beyond the mouth of the carbs where the short leg can be freely turned 360 degrees.

Slick
 
Last edited:
Found a set of '65 Atlas 389 (1-1/8") carbs. Still looking for a smaller set.


IMG_5942.jpeg
 
Last edited:
You must log in or register to reply here.
Back
Top