My MM won't start

[CJM1945]

My MM has been standing for 3 years and I am preparing her for an MOT. Although in good original condition, she just refuses to start. If I spray Bradex into the carb inlet, she will fire for an instant then die. Fuel pump is working fine. Float chamber level is OK. Carb has new (correct) needle and jet and seems to be fine. Ignition electrics are OK. What's going on? Is she just in a mood or has her petrol "gone off" after 3 years? HELP!

[mike.perry]

Have you tested the piston by lifting it and checking that it drops smoothly on to the bridge?
Have you filled the dash pot with oil?

[chickenjohn]

the float bowl / pipe to the jet from the float bowl may be blocked with silt!

Take the carb off the car remove the piston and needle, clean everything inside the carb and especially the float chamber with carb cleaner (and if you have one- an air line and a blow gun) and blow any silt out via the jet.

your car will then start.

[charlie_morris_minor]

i would be looking to drain the tank and replace it with fresh petrol.

[rayofleamington]

If petrol is getting through the carb (i.e. you can get the plugs damp) but it still won't fire on the old petrol, then it's likely to be stale petrol.

easy check for proof of theory: 'Carefully' splash some neat petrol into the mouth of the carb - the engine should fire up.
splash some of the old petrol into the carb mouth - if the result is no firing or barely firing then the old petrol is your cause.

[bmcecosse]

As above - pour some fresh petrol down the carb throat and crank it - obviously the ignition is working since you say it runs when you spray flammable gas. Once it starts it should burn the stale petrol ok - but fill up with fresh stuff asap.

[micstersmoggy]

petrol has a shelf life of about six months then it goes to a kind of jelly surprising i know but this was told by a man who knows these things petrol chemical main man who said change it after 6 months if not used. although i have never had problems with old petrol he said new petrol is different.

[bmcecosse]

It certainly doesn't go to 'jelly' - my cars stand all winter (9 months in one case) with almost full tanks and always start up just fine when required...... But over a long period the lighter fractions can evaporate -especially in warm weather - and this is what can make the engine difficult to start from cold.

[mike.perry]

The price of petrol today I certainly would not be throwing any away.
I wonder how my jerrycan of 4 star is getting on?

[rayofleamington]

A fully sealed jerry can should be fine - especially if it is full!

A one third full car petrol tank is different - the 'air' in the tank expands and contracts day and night (it's usually warmer during the day..) which causes the tank to 'breathe' (on a Minor it breathes through the filler cap). This exhausts the volatile gases out of the tank allowing more and more of the lighter components to evaporate.

I've only ever had stale petrol once (1996 I think) and it took over a year - I've not had the issue in the last 10 years and many of my cars stand for a very long time so I've always wondered if there were the occasional 'dodgy blend' of fuel that was more susceptible. Probably just paranoia.

[katy]

My MM has been standing for 3 years

That's more than enough time for the fuel to go stale. As others suggested drain or pump it all out and replace with new.
Don't throw the old fuel away, blend it about 1 to 10 with new fuel and use it that way.