vacuum advance

[moggiethouable]

I had one of those intermittent rough running faults on my 1098 and ploughed through all the usual, you know, plugs, points, fuel pump, condenser.Even the coil (sorry BMC)
Anyway it would not smooth out, so in desperation I wondered if I had an air leak on the manifold or some such.
I have access to an audio leak detector and lo and behold the rubber attaching the vac pipe to the carb had split out of sight underneath.
I replaced it and hey presto she runs like a train again.
I consulted the manual but it gives precious little information on what said pipe does and how though, so could some one explain its purpose in life please?
Thanks as always chaps and chapesses.

[drivewasher]

The vacuum created by the inlet air being drawn in through the inlet manifold creates a vacuum. This vacuum is used to pull on a diaphragm in the distributor that pulls the plate the points are fixed to thereby advancing the ignition timing to suit the engine speed and power demand. As the vacuum varies.

Basically!

[moggiethouable]

thankyou.
the small vessel then that is in this vac line, connected by way of mounting to the engine via a mounting bolt, is that simply a reservoir?

[Bidz]

thankyou.
the small vessel then that is in this vac line, connected by way of mounting to the engine via a mounting bolt, is that simply a reservoir?

I think it's some sort of filter! To stop fuel entering the ignition system?

[drivewasher]

It's a flame capture tank iirc so if any fuel vapour ignites in the vacuum tube it doesn't send the advance diaphram in the dissy to the moon!

BMC may be able to enlighten upon this but the later engines had a simple nylon tube from carb to the dissy with rubber push on ends and no vapour trap

[moggiethouable]

Thanks again.
Its funny all these comments ring faint and distant bells.

[bmcecosse]

So - to test the dizzy vacuum unit, you need to suck the pipe - and watch to see the plate in the dizzy move and relax. I guess they just decided a 'fuel trap' wasn't necessary - perhaps the diaphragm was changed to something that would resist petrol .

[drivewasher]

iirc the nylon tube only is push on at the dizzy end as well the flametrap steel one is threaded

[mike.perry]

Interestying result when fuel does get into the vacuum pipe and then the distributor, there is a small explosion when the points spark ignites the fuel and the engine stops. Lifting the bonnet reveals the distributor in pieces

[moggiethouable]

Interestying result when fuel does get into the vacuum pipe and then the distributor, there is a small explosion when the points spark ignites the fuel and the engine stops. Lifting the bonnet reveals the distributor in pieces

Very good, I have a mind to replace the pipe with a new one to ensure good fitment both ends and think I will retain the services of the explosion trap

[dalgrae]

After reading these posts and never been completely happy with the battered run/appearance of the metal pipework on my advance/retard with flame trap I removed it from my car to fit new pipework I had left over from my model steam engineering days ,as I was lifting the assembly from the car petrol poured out of the pipe end that connects to the carb .I know until recently my car has been running rich (now cured) but I shocked to see this petrol it also smelt really bad so I assume it had been sitting in the flame trap capsule for some time

[bmcecosse]

" model steam engineering days " - do tell us more...... with pictures!

[dalgrae]

So far I have built a 3 1/2 gauge Rob Roy saddle tank then I built a 5" gauge Speedy GWR based on the 15XX class which easily pulled 25 passengers on the Ashton Park track the finished weight was approx 80 KGS ,now I am in the process of making a 3 1/2 gauge Southern Schools 3 cylinder engine ,so far the frames are done wheels on cylinders made and attached rods made ,I also decided on this loco to use miniature needle rollers rather than plain bush bearings to try and improve the efficiency of this loco and improve the rolling ersistance the 5" gauge loco was tested behind a dyno car at 3/4 % efficieny which I was told was fairly good

[bmcecosse]

Excellent! I am of course named after 'Rob Roy'.... Some pictures would be great - I'm sure all would appreciate them. I am in complete awe of anyone who can do these things - I can't even drill a straight hole......

[moggiethouable]

Received a new piece of rubber pipe today from ESM for the princely sum of £4.74, the pipe was only £1.20 the rest was carriage.
However I have enough pipe for 3 vehicles, this is the short stubby rubber pipe connecting the carb to the copper vac pipe.
So if anyone has the same problem I can post a bit on F.O.C.

[drivewasher]

I think the pipe you have bought is not to make the conection between carb and the microcopper pipe, as that connector is a seperatley sold one that has a very small end for the micropipe and a larger one for the carb "spout"
I think what you now have is a length of rubber(ish) pipe that will fit onto the microcopper tube so as to extend the shorter version of the flametrap assy thet ESM sell and declare that the shorter end from the capsule to carb is too short as the origonal correct length one is no longer available. That's why the tube is long as it's an extension for the copper tube. I assume you need to cut off a short copper tube to connect the rubber extension into the carb connector.

Oh! Iv'e made myself dizzy now lol...

[moggiethouable]

I think the pipe you have bought is not to make the conection between carb and the microcopper pipe, as that connector is a seperatley sold one that has a very small end for the micropipe and a larger one for the carb "spout"
I think what you now have is a length of rubber(ish) pipe that will fit onto the microcopper tube so as to extend the shorter version of the flametrap assy thet ESM sell and declare that the shorter end from the capsule to carb is too short as the origonal correct length one is no longer available. That's why the tube is long as it's an extension for the copper tube. I assume you need to cut off a short copper tube to connect the rubber extension into the carb connector.

Oh! Iv'e made myself dizzy now lol...

Blimey, I feel a bit off centre myself now.
Thanks for that, the tube is an interference fit both ends though and is almost identical to the tube I removed, it like the original has a 2.5mm i.d. both ends.
The outlet from the carb is a barbed connector, the tube from the flame trap is just 3mm o.d. copper pipe.
I shall give the car a run out tomorrow to make sure its the biz.

[drivewasher]

Thats interesting, I bought the proper short connector and it's only just tight on the copper tube, I'm expecting to have to fettle it sooner or later