Various Carb Hoses

[Nasher]

Hi all.

Was tinkering with my 97 M900 today, doing yet more tidying up from previous owners 'mods' and had a good look around the Carbs following a couple of threads on here about Vacuum hoses etc.

As the bike is a 97 model I’m quite sure it shouldn’t have a Vacuum fuel tap fitted and sure enough the inlet manifold for the horizontal Cylinder doesn’t have a Vacuum take off. The Inlet manifold for the vertical Cylinder does have one and it’s connected to the fuel pump.

There is also of course the fuel inlet pipe from the fuel pump to the ‘T’ connection between the carbs.

Then there are the various breather/outlet pipes:

Firstly the Float chamber drain pipes. These I’ve already replaced with Stainless over-braided hose, which is a bit OTT, and I’m thinking of just removing them as I can push a length of hose onto each one to drain the float bowls if I ever need to.

Then I need some wisdom from those more experienced with ‘our’ bikes.

The fuel overflow hose from a ‘T’ piece between the carbs just behind the Fuel inlet ‘T’ has been cut to @3in long and drips onto the top of the Horizontal Cylinder if I leave the fuel tap on too long without the engine running.
How should this be routed?
I’m probably going to add a longer pipe and route it down the left side of the engine.

Next are the two breather pipes from the Diaphragm chambers with the inline valves and over-springs.
These look like they’ve been cut short after the valves and again just dangle over the Horizontal cylinder.
I’m sure these should be protected somehow from low/high pressure around the bike to ensure consistent pressure difference across the Diaphragms, but don’t know what the standard setup is.
Anyone have some images?

Thanks

Nasher.

[Dukedesmo]

Originally Posted by Nasher

Next are the two breather pipes from the Diaphragm chambers with the inline valves and over-springs.
These look like they’ve been cut short after the valves and again just dangle over the Horizontal cylinder.
I’m sure these should be protected somehow from low/high pressure around the bike to ensure consistent pressure difference across the Diaphragms, but don’t know what the standard setup is.
Anyone have some images?

Are these the ones that go to the little plastic boxes? at least on standard bikes. Have they been removed?

[Nasher]

Thanks Dukedesmo, but:

Originally Posted by Dukedesmo

Are these the ones that go to the little plastic boxes?

What Black Plastic Boxes?

Originally Posted by Dukedesmo

Have they been removed?

Probably, but I don't know what's supposed to be there which is why I asked the question.

Nasher.

[Dukedesmo]

Originally Posted by Nasher

Thanks Dukedesmo, but:


What Black Plastic Boxes?


Probably, but I don't know what's supposed to be there which is why I asked the question.

Nasher.

In the pic above a small grey triangular plastic breather box between the frame rails near the headstock, one on each side that the carbs 'breathe' into.

I'm sure many remove them but I think the carbs need to vent somewhere where there's no big air/pressure movements.

[Nasher]

Thanks for that.

Does anyone have any close up images of these breather boxes?

I might make myself a little polished Aluminium version.

Thanks

Nasher.

[Dukedesmo]

I've got a pair that I removed from mine, no use to me as I've got different carbs and bike will never go back to original - it's too far gone and much better as it is.

They're a fairly low-rent item, you can have them if you want or I can take pics if you just want the idea?

[utopia]

I was going to make the same offer.
My diaphragm breather tubes had little plastic "filter" (?) modules halfway along them.
I re-routed the tubes so they terminated behind the battery.
I terminated them in the filter modules (keeps the spiders out ?) which I then cable tied to the coil/CDI mounting bracket.
They seem to be nicely out of the wind there and have been like that for 5 or 6 yrs with no discernible issues.

[Dukedesmo]

I have to say that even if I had the standard carb setup, I'd be ditching the boxes anyway because they are (IMO) ugly and as per Utopia's setup you can do without and still avoid pressure related problems.

Of course if you want to get your bike absolutely original then boxes are required and as I said they're free to a good home, as it would seem, are Utopias.

Ground off the lugs for mine so even when I'm running stock carbs I won't be having those bits of tat sticking out the sides

If I've still got then you are welcome to them

[Nasher]

Guys

Thanks for the input and offers of parts, I'm sorry I should explain myself better.

The bike isn’t standard, and I have no intension of putting it back to standard.
It doesn’t have any Breather boxes, airbox and a few other bits.

I am in the process of making good and tidying up various mods(often bodged) that have been carried out by previous owners, and often my trouble is I’ve never owned a standard M900 so don’t understand what’s missing or has been modified.

On top of the cosmetic stuff there are a few mods that have been done badly enough to actually hinder performance, or are just dangerous.
Mostly daft stuff like all the current to the coils going through a length of VERY thin wire, the up-rated regulator connectors melting because they had been bridged with too small cable, and the bracket that had been made to support the battery box once the airbox had been removed which didn’t support anything as it just flexed and the battery was held in place by the underside of the tank. The routing of the throttle cables around the headstock was wrong to the extent that the engine revved on full right lock, the back wheel being in the swinging arm diagonally and the Vertical cylinder HT being pinched and split, etc etc.

The bike is running so much better than it did but I want to make sure nothing else is causing problems.

The fuel overflow pipe is easy, I can just extend it down rather than it drip onto the top of the horizontal cylinder which I think is dangerous.

I wanted to understand how the breather box for the other two pipes protected the ends, plus how and where it is vented to atmosphere in a ‘still’ environment.
I don’t want ugly Black Plastic boxes sticking out the side of the bike, but a small polished aluminium canister in the right place wouldn’t look out of place.

Nasher

[Mr Gazza]

When I owned my '98 carbed M900 I hated those little grey boxes.

I reckon you could shift a few if you made some nice ally replacements Nasher...Nobody seems to like the originals.

Or maybe an opening there for someone who could make carbon ones?

[Darren69]

I'd just do what Utopia has and route them behind the battery or somewhere out of a strong air flow.

[Dukedesmo]

Out of curiosity I've just been looking at the boxes and noticed that they are very different in terms of fitting, not sure why as I never ran the bike with them.

One has a push-on pipe fitting where the other has 4 holes, both have what I assume are drain holes, presumably there is a reason for the difference and maybe someone can shed some light on this?

here's a pic;

[Darren69]

I never fully understood why they were there tbh. I never had any on my 750 and 900SS which had the same carb setup.

At least as far as my addled brain will let me remember. There were later float bowls with oil heaters (which I retrofitted and did nothing btw )

[Nasher]

Had an interesting effect of tidying up some of this over the weekend.

As mentioned the overflow/breather pipe from the Carb float bowls was just a few inches long and directed straight down on top of the horizontal cylinder.
I replaced this with a longer length of the correct bore pipe and ran it down the left side of the engine.

When I went out for a ride everything was OK until I got onto the motorway, then after @1/2 a mile or so the bike slowed down, wouldn’t rev, became hesitant and felt like it was running out of fuel.
I pulled over onto the hard shoulder, checked the fuel tap was fully on etc and tried again. As before it was OK for @1/2 Mile then started to hesitate etc.

I pulled over again, and knowing the only thing I’d changed was the breather pipe, I cut it off with my penknife under the Carbs where it was before.
Of course the bike was fine after that and ran like a train for the rest of my ride.

Obviously the position of the end of the breather hose is critical, in that there will be areas of high and low pressure around the bike that will travel up the pipe and effect the float height in the Carbs, and possibly even the pressure differential across the Diaphragms.
At higher speeds the float height was obviously effected to the point where it was so low, after being used up and not replenished, that the bike was starved of fuel.

I can honestly say I’ve never seen this with a modified Carbed bike in all my 30yrs of mucking about with them.
I have seen a Carb breather pipe from a tuned outboard boat engine suck splashed seawater up into the float bowls when the owner decided to route the pipe through the tray instead of letting it drain into the tray and down the leg.

Nasher.