Inlet manifold balance stubs.

D

DougC

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Are the balance pipe stubs cast, pressed, or screwed into the 30-32mm 850 inlet manifolds, before I start hitting them with a hammer.

The balance pipes on mine are quite badly pitted from corrosion. The pitting is currently filled with epoxy, to ensure a good seal to the rubber balance pipe.

I’ve been considering making a new pair of stub pipes, but how I do that will depend on how removable the existing ones are from the manifolds.

Anyone tried this?
 
I am fairly sure they unscrewed on the RH4 manifolds I straightened.
They might have had some form of 1/4" thread.

Inlet manifold balance stubs.
 
I cut them off and filled the holes with epoxy. Then drilled and tapped new holes for some balance tubes up above the centerline angled toward each other and connected the tubes with a short piece of vacuum hose. Not suggesting anyone else do it, but you could alternatively cut them off, drill out what remains, and tap for whatever size hose fittings you want at the stock locations.

These are modified manifolds obviously, but the balance tubes were moved from the bottom to the top. The theory being the tube never fills up with fuel with the balance tubes located above the centerline. Probably doesn't make a farts worth of a difference, but I like to tell myself that it does.

Inlet manifold balance stubs.
 
At least on the 32x32mm manifolds, they are pressed in. Heated to 200F and used a punch a little smaller than the OD, punched it out easily from the inside. An appropriately sized tube could be threaded and the hole tapped to make a threaded version. If you can find the right tube, they press in even easier. You might ask AN - they might have a source for the tubes since they have manifolds made. It's also possible the the earlier threaded one L.A.B linked might be slightly larger and the manifold could be tapped for them.

1732308660839.webp
 
marshg246 said:
At least on the 32x32mm manifolds, they are pressed in. Heated to 200F and used a punch a little smaller than the OD, punched it out easily from the inside. An appropriately sized tube could be threaded and the hole tapped to make a threaded version. If you can find the right tube, they press in even easier. You might ask AN - they might have a source for the tubes since they have manifolds made. It's also possible the the earlier threaded one L.A.B linked might be slightly larger and the manifold could be tapped for them.

View attachment 117379
Click to expand...
Excellent, thanks.
That lets me plan ahead, for the next time the carbs are off.
I'll probably just make new tubes, and press them in.
 
Schwany said:
I cut them off and filled the holes with epoxy. Then drilled and tapped new holes for some balance tubes up above the centerline angled toward each other and connected the tubes with a short piece of vacuum hose. Not suggesting anyone else do it, but you could alternatively cut them off, drill out what remains, and tap for whatever size hose fittings you want at the stock locations.

These are modified manifolds obviously, but the balance tubes were moved from the bottom to the top. The theory being the tube never fills up with fuel with the balance tubes located above the centerline. Probably doesn't make a farts worth of a difference, but I like to tell myself that it does.

Inlet manifold balance stubs.
Click to expand...
I would worry about the epoxy coming loose and flying into the motor. How about threading in a button head allen?
 
seattle##gs said:
I would worry about the epoxy coming loose and flying into the motor. How about threading in a button head allen?
Click to expand...
The epoxy hasn't flown out in 2500 miles, but yes button head allens would be better. I've thought of doing exactly that many times, but done nothing about it due to coming up with other hair brained ideas to improve the old Norton ride. I'll probably do it before this year is out once I clean up after the last storm in my neck of the woods.

Not relevant to this thread, but I have a hole plugged with epoxy inside the left side intake port in the head where the port work hit an air pocket in the casting. I didn't do the port job, but I did fill the hole. Fred Barlow got a little carried away with whatever he was using to open the ports up near the guide. The epoxy has been in there for 13K miles since the early 1990's and never come loose. Engine doesn't suffer for power anywhere contrary to well intended advice on the internet about not doing port work in Norton heads.
 
Last edited:
Dano said:
Are these stubs needed. What if you were to leave off and filled the holes.
Click to expand...
The old twin Mikuni adapter intake manifolds for Nortons did not have balance stubs. When I was using twin Mikuni carburetion, I added stubs and a balance tube. A placebo effect was about all I got out of it. I told myself the idle was better, but it wasn't all that bad to begin with.

I think it makes a difference with Amal twin carburetors. If you have a desire to test running Amals without the tube connected, use rubber vacuum tube caps secured with safety wire so they don't blow off if the engine should backfire.
 
Schwany said:
The old twin Mikuni adapter intake manifolds for Nortons did not have balance stubs. When I was using twin Mikuni carburetion, I added stubs and a balance tube. A placebo effect was about all I got out of it. I told myself the idle was better, but it wasn't all that bad to begin with.

I think it makes a difference with Amal twin carburetors. If you have a desire to test running Amals without the tube connected, use rubber vacuum tube caps secured with safety wire so they don't blow off if the engine should backfire.
Click to expand...
When I hook up my Morgan Carbtune Pro sync tool to the inlet balance pipes, there is no longer any connection btwn the inlets and the idle is noticeably poor while performing throttle balancing. Twin Amal concentrics seem to like/need the extra pressure drop when one side is no longer flowing while inlet valve is closed. Supposedly helps to keep fuel up in the pilot circuit ready for next intake stroke.
That said, my single clyinder 500 cc Velocette seems to idle nicely with a 928 Amal concentric.
 
Tornado said:
When I hook up my Morgan Carbtune Pro sync tool to the inlet balance pipes, there is no longer any connection btwn the inlets and the idle is noticeably poor while performing throttle balancing. Twin Amal concentrics seem to like/need the extra pressure drop when one side is no longer flowing while inlet valve is closed. Supposedly helps to keep fuel up in the pilot circuit ready for next intake stroke.
That said, my single clyinder 500 cc Velocette seems to idle nicely with a 928 Amal concentric.
Click to expand...
Just reminded me...
I cut the long pair of brass tubes that came with my old Motion Pro sync stick to use as balance tube stubs on the 32mm Norton intake manifolds I modified for 35mm FCR carburetors on my P11. I don't use the sync stick on anything I currently own, so that worked out.
 

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