Intake manifold question

[Michael Oritt]

I recently sent my H6 carbs and intake manifolds off to Tom Bryant for refurbishing. Tom just contacted me asking what was the purpose of the nipples on bottoms of the manifolds (see pictures). I told him that there is a 12 or so inch long copper tube (not shown) attached to each nipple running down past the exhaust manifold.

This is the way the car came to me in 1999. The car was converted to M specs in 1957 by the first owner and I have always assumed these tubes were a part of the M conversion. Tom questions why the fuel system would be vented to atmosphere and though I have wondered about this myself I never thought to investigate further. He is recommending I plug the holes and I agree--at best the tubes make R&R-ing the carbs that much more difficult.

Any input will be appreciated.

 

[TodE]

Michael, I almost feel intimadated answering the guru of Healey's! when I am such a rookie!! I believe they are drains, so if the carbs/intake manifold load up with fuel they drain below the exhaust manifold instead of pouring onto the hot exhaust. Great job on your articles in the "Healey Marque Magazine"

 

[John Turney]

The regular 6-cyl manifolds have those for draining excess fuel. I don't know about the tricarb manifolds. Normally, the drain tubes are so long and thin that little air is drawn in through them.

 

[steveg]

The real question is how much do these drains affect running? If air is only sucked in during high vacuum, i.e. going downhill with the butterflies closed, how much does it lean the engine out during normal running?

Or is none of this a problem because when the carb richness is set, the setting always includes compensation for any air sucked up the drains.

Are Healeys the only cars with these drains?

 

[GregW]

The regular 6-cyl manifolds have those for draining excess fuel. I don't know about the tricarb manifolds.

I'm gonna say no.

 

[Michael Oritt]

John T said "The regular 6-cyl manifolds have those for draining excess fuel." (emphasis added)

Questions:

1. What is "excess fuel" and why, if my float levels are set up properly, would I ever have any unvaporized fuel seeping down into the manifold?
2. How about what Steve asked--do other cars beyond Healeys have these?

 

[Bob_Spidell]

... would I ever have any unvaporized fuel seeping down into the manifold? ...

It can happen. At the start of a long road trip a few years ago we stopped for lunch in Marysville, CA and when we came out of the restaurant, there was a puddle of gas just below both (IIRC) of these drains; enough gas to make a pretty good fire if there was a source of ignition. Car had never done this before--except, maybe when it was a cold day and I had to 'choke' the engine to get it started--and never did it again (when warm). The usual justification for oddball, Healeys-only stuff is "Well, the BMC beancounters would not have allowed such an extravagance if it wasn't absolutely necessary."

A float needle valve stuck open for some reason might raise the fuel level higher than the top of the jet and could cause this. Note we also have overflow drains on the float chambers and, offhand I don't recall anything similar on fixed-choke carburetors.

 

[EricG]

Early Sunbeam Alpines (Series 1+2) had a thin copper drain line at the bottom of the intake manifold. It was long enough to clear the exhaust manifold and it also had a small one way valve at the end of the drain line. Rarely does fuel leak from this. Luckily?!
Eric

 

[steveg]

The regular 6-cyl manifolds have those for draining excess fuel. I don't know about the tricarb manifolds. Normally, the drain tubes are so long and thin that little air is drawn in through them.

...or the early BN4 2-port.

 

[John Turney]

Bob is correct. I'm not an expert on H6s, but on HD8s, the normal fuel level is about 4mm to 5mm below the bridge. If the float valve sticks, the level in the bowl only has to rise by that 5mm to overflow into the carb throat to start into the manifold. The top of the float bowl is at least 7/16" above the normal fuel level where the carb overflows would come into play.

 

[Keoke]

Somewhere on this forum is a drawing of these drains , I tried to resize it to post but none of my programs work on it ???

 

[AUSMHLY]

The regular 6-cyl manifolds have those for draining excess fuel. I don't know about the tricarb manifolds. Normally, the drain tubes are so long and thin that little air is drawn in through them.

I believe both drain tubes should be Z shaped.