Vacuum switch, Diaphragm problems

[B509VTA]

My 1300 maestro has recently started running erratically. I have managed to trace the fault to a broken diaphragm in the vacuum switch.
I have contacted all the local scrap yards to get a replacement without success. I have also contacted the local Rover Parts dealer who has informed me that the vacuum switch cannot be purchased separately but only as part of a complete carburettor at some ridiculous price.

Does anyone have or know of a place where I can get hold of the vacuum switch?

Thanks in advance

[H48HPE]

Hi

When I desperatly needed a new sump for my 1.3 and couldnt find one anywhere I got one mail order from maestro and montego parts and salvage

link (http://www.montego-and-maestro.co.uk/)

give them a ring and they might be able to help.

your alternative would be to convert to a manual choke without an ecu etc. all the parts for that will be in the scrapyard.

Andy

[Simon]

If your 1.3 car is a 1984/5 non-HLE then, from an MG Rover dealer you could order a new one under part number LZX 2072 (Vac switch "P"). If it is an HLE then you could try ordering LZX 2073 (Vac switch "Q"). They will be in the region of £25. These parts were available a couple of years ago when I needed one, but I guess things might have changed since then.

[MGTurbo]

The vacuum switch is more trouble than it's worth. Bypass it by looping a section of hose from port to port. Remember to block off the vacuum take off on the manifold. Problem solved.

Gareth

[G Force]

Originally posted by MGTurbo
The vacuum switch is more trouble than it's worth. Bypass it by looping a section of hose from port to port. Remember to block off the vacuum take off on the manifold. Problem solved.

Gareth

If you modify the carb in this way you are going to introduce a huge flat spot and poor acceleration when the engine is cold, the affect will be more noticable on certain models but will apply to all. I have acheived reasonable results by fitting a small jet into the loop pipe as you are suggesting but never managed to get anything like the drivabillity of a carb with a vac switch fitted, and the jet sizes varied from model to model and car to car making a diy job hard to recomend.

A good switch I found worked ok in most models was LZX 2292 ( Z )

Gary ;)

[MGTurbo]

Originally posted by G Force
If you modify the carb in this way you are going to introduce a huge flat spot and poor acceleration when the engine is cold, the affect will be more noticable on certain models but will apply to all. I have acheived reasonable results by fitting a small jet into the loop pipe as you are suggesting but never managed to get anything like the drivabillity of a carb with a vac switch fitted, and the jet sizes varied from model to model and car to car making a diy job hard to recomend.

A good switch I found worked ok in most models was LZX 2292 ( Z )

Gary ;)

Funny how they deleted the vacuum switch on later models as well as the fuel cut-out switch? This huge flat spot you describe will only happen if the car was set up lean to compensate for the richer mixture produced by the vacuum switch, especially if any adjustments were done whilst the switch had failed. I did this mod to my 1.6 VP and to a mate's 1.6 and it never had a flat spot, although i do know how to use a screwdriver to set up the idle mixture by ear, not every can do that.

Gareth

[G Force]

Originally posted by MGTurbo
Funny how they deleted the vacuum switch on later models as well as the fuel cut-out switch? This huge flat spot you describe will only happen if the car was set up lean to compensate for the richer mixture produced by the vacuum switch, especially if any adjustments were done whilst the switch had failed. I did this mod to my 1.6 VP and to a mate's 1.6 and it never had a flat spot, although i do know how to use a screwdriver to set up the idle mixture by ear, not every can do that.

Gareth

I dont dissagree that the poor reliability of the vacuum switch prompted a change in the design of the system, but the later models did not need a vacuum switch because advances in engine management systems meant that accelaration enrichment could be provided by the ecu indexing the stepper motor additional steps whilst on choke.

You are wrong to suggest that cars modified in the manner you describe will not have a flat spot when cold, and anyone who cares to try it will bear me out on this.

As for the two cars that you modified if the only problem was the vacuum switch then after your mod the idle mixture when hot would not normally need adjusting. I suspect that you set the mixture too rich, but not that I expect you to accept my opinion.

Gary ;)

[topgear]

calm down guys, its just a car!:eek:

[G Force]

Perfectly calm dude :cool:

Gary ;)

[topgear]

:cool:

[MGTurbo]

I dont dissagree that the poor reliability of the vacuum switch prompted a change in the design of the system, but the later models did not need a vacuum switch because advances in engine management systems meant that accelaration enrichment could be provided by the ecu indexing the stepper motor additional steps whilst on choke.

What difference is this going to make when the engine is hot? If the choke comes on when hot there is a problem. The stepper motor will only increase the idle speed in this case, before the point at which the emulsion tube holes line up for extra enrichment when cold.

You didn't state if where this flat spot occurs, i.e hot or cold, which is where we may be getting our wires crossed.

I'm simply making a cost saving suggestion, the valve was troublesome, failing at all times hot or cold, and if people were to get a flat spot when cold, this could be compensated for in the way in which i described, but going on MY past experience, flat spots havent been a problem with removal of the valve, and my idle mixtures have never been above 2.5-3%.

It's certainly worth trying, it's a well known modification.

Gareth

[G Force]

We have always been talking about cold running on choke. Once the car is warmed up the vacuum switch does not have any affect on fuel metering.

All the vacuum switch is, is a pressure operated choke variable air correction jet if you like. if you remove it, it is like fitting one very large air corrector jet the size of the internal diameter of the pipe stub if you get me. This substantially weakens the mixture when cold. ;)

Cheers Gary :)

[BIGLAD]

Originally posted by B509VTA
My 1300 maestro has recently started running erratically. I have managed to trace the fault to a broken diaphragm in the vacuum switch.
I have contacted all the local scrap yards to get a replacement without success. I have also contacted the local Rover Parts dealer who has informed me that the vacuum switch cannot be purchased separately but only as part of a complete carburettor at some ridiculous price.

Does anyone have or know of a place where I can get hold of the vacuum switch?

Thanks in advance

Hi,
I may still have a couple of New 1300cc Carbs. I can't remember if they have the vacuum switch still on them though! I will check later on this week and also check the part number on the carb tag to see if they are suitable for your model.
Thanks Biglad;)

[BIGLAD]

Originally posted by BIGLAD
Hi,
I may still have a couple of New 1300cc Carbs. I can't remember if they have the vacuum switch still on them though! I will check later on this week and also check the part number on the carb tag to see if they are suitable for your model.
Thanks Biglad;)

:)
Hi,
I have a few New Maestro/Montego 1300cc Carbs.
They still have the Vacuum Switch and the Stepper Motors on.
Any one interested, send me a P.M.
Thanks,
Biglad.

[B509VTA]

Thanks for all the info.

I have recontacted my local Rover parts dealer aimed with the part no (LZX 2072).

They are now able to supply me a vacuum switch which I will collect tomorrow.

Seems strange that they cannot supply a vacuum switch but can supply to a part number !!!