Bimota Forum

[Lozza212]

Hi all,
Mantra Engine Hoses:
Does anyone know if the fuel tank is pressurised by one of the vacuum hoses from the manifold ?
I used low pressure air to check that all the vacuum lines were clear .
When I blew through the barbed fitting under the rear of the tank the LH one goes to the filler scupper / overflow , no problem there.
When I blew into the RH barbed fitting it pressurises the tank ? weird.
When I open the filler - whoosh- pressurised.
Is this normal ? Why would you need to pressurise the tank ?
With the carbs so high up and only a very weak fuel pump maybe it is normally pressurised to ensure sufficient fuel supply to the carbs? but still weird to me .
Maybe the vaccuum crossed over somewhere ? or maybe the tank cap vent is blocked, next item to check.
But everything looks normal and untouched from new to me .
After all it is a Bimota and different.
Look forward to replies,
Cheers
Laurie

[Lozza212]

Hi again ,
Just had a look in the parts manual for the vacuum hose setup.
This is standard by the look of it as the parts book shows an "idle jet" in the both vacuum lines from each manifold .
Does anyone know why these jets are in the manifold vacuum lines .
I'm presuming something to do with the "idle settings" going by the name of the part in the parts book.
I have only found the one on the RH side, but will have to check the old hose for the left as I have replaced it with a new one. The original hose was rock hard.
Cheers
Laurie

[brian]

To my knowledge the tasnk shouldn't be pressurized. It should be vented to atmosphere via a breather. If its the same as DB4 etc, it just gravity feeds to the little vacuum operated fuel pump on the bottom of the tank.

I have no idea what the 'idle jets' in the manifold vacuum lines would be. On DB4 there is one vacuum line that comes off one of the intake manifolds to power the vacuum fuel pump. The barb on the other intake manifold is capped. These barbs are used for connecting vacuum gauges to synchronise the carbs.
_________________
'99 DB4 #104, '96 SB6 #1165, '94 DB2 J #652, '99 DB4 #088, '08 VTX1800, '93 ZXR750R M1, '95 ZXR750, '95 ZXR750 Race Bike, '94 CBR400rr NC29 Race Bike, '94 CB250, '49 BSA C10 250, '61 BSA A10 650, '89 ZXR750, '91 Ducati 851

[Lozza212]

g'day Brian.
I am thinking this is all part of an emissions system .
This is what have found:
Tank internal vent exits via the barb fitting under the RH side of the tank to the carbon canister in the seat ducktail.
The filler neck scupper ( overflow when filling up too much ) exists on the LH side barb under the tank to the ground.
In the RH hose from under the tank to the carbon canister is a filter/check valve .
There is also second hose that runs to the carbon canister from the LH & RH intake manifolds. Same side of the canister.
This second hose also tee's off to run the fuel pump .
There is an outlet hose on the other end of the canister that vents to atmosphere.
In the hoses from the manifolds ( LH & RH) are the previously mentioned "idle jets - marked 50 with makers logo INC stamped on the end face.
I suspect that when pressure builds up in the tank it escapes through the canister , thus reducing emissions.
One Ducati forum says that the carbon canister can become clogged over time and then the tank pressurises, but i doubt this is the case due very low mileage.
I think that when I was checking all the lines with the airgun I assumed like you would that the tank vents direct to atmosphere.
I don't think this is the case with the Mantra, it is now obvious that it vents through the carbon canister.
Could have something to do with emissions laws in California, but it is a standard part in the parts catalogue, so maybe universal.
I still don't understand the reason behind the "idle jets" in the manifold hoses yet, but working on it. Something to do with pressure reduction / damping to drive the pump and maybe something else with the carbon canister.
Sorry to bore you with all of this, but maybe someone else can shed some tech info on the workings of the system.
Cheers
Laurie

[Lozza212]

Hi Brian,
I forgot to mention that I am using a Carbtune on the bike , hence the removal of the LH and RH vac hoses & fittings on the Lh and RH manifolds.
Does the DD4 have a carbon canister in the tail ?
Cheers
Laurie

[brian]

Hi Laurie,

That now makes a little more sense... I'd say your bike was built to comply with Californian emissions rules. If it were my bike, i would delete all of that stuff including the carbon canister. Might be worth opening the carbs to check the jetting and setup as well. None of my bikes have a carbon canister.
_________________
'99 DB4 #104, '96 SB6 #1165, '94 DB2 J #652, '99 DB4 #088, '08 VTX1800, '93 ZXR750R M1, '95 ZXR750, '95 ZXR750 Race Bike, '94 CBR400rr NC29 Race Bike, '94 CB250, '49 BSA C10 250, '61 BSA A10 650, '89 ZXR750, '91 Ducati 851