Help with MPG

[Jawelnofine]

Hi Mickey,
I'll have my 2cents of a say...
Often overlooked but very obvious, check your dashpot and piston in the carburettor for full and free movement....no sticking.
I would polish it and the bore and then on reassembly, use about 1/2 a teaspoon of the SU oil in the dashpot.
This and even the slightest of fuel leaks all add up to wasted fuel. Hint....check the braided fuel line...I've had these leak without being visually obvious.
Hope this is of some value.

[bmcecosse]

You should NOT polish the carb piston or 'bell' - as long as it slides up with finger pressure and falls back with a nice clunk - it's fine. Don't fiddle with it. It should be filled up (much more than 1/2 teaspoon) with 3 in 1 oil to within 1" of the top. It will then expel any oil it doesn't need to set it's own level. 1/2 teaspoon is not nearly enough to give the necessary damping. It' s always worth inspecting the petrol tank - it can go porous - especially on the top surface, with obvious loss of fuel - and dangerous fumes! But just how bad IS the fuel consumption???

[Jawelnofine]

Hi BMC,
Polishing the piston and Bell....guess that's just the biker in me (sorry). Mine was all tarred up and sluggish. I had to do something it's a lot better now. But I will add more oil. (thanks for that tip)
I believe Mickey said he was getting 25 mpg. Seems to be a serious loss somewhere.

[bmcecosse]

Oh CLEANING is fine - but polishing suggests use of abrasives which is not a great idea, although may be necessary (Brasso only!) if the piston proves sticky in the bell even when spotless. 25 mpg may be all it will do in cold weather/short runs/town driving.

[rayofleamington]

It's there party as an economy device. If it's not working then the engine will be 'flat' and unresponsive. And poor on economy!

Vac advance doesn't increase power / response at all - it just allows better fuel economy. At light throttle the engine has a reduced tendency to pink, so timing advance gives a bit more power for the same fuel.
If it's not working you get the same mid range power with a tiny bit more throttle, and absolutely no difference at all at full throttle.

[chickenjohn]

I would get ~30mpg out of my 948 (less in winter) but could get 42mpg on a long run at 55-60mph.
That was with everything standard and with crossply tyres. The tyres were not well balanced so I didn't often go over 60mph
Having the wheels balanced was low priority as the car was full of filler and fibreglass and is one of only 2 minors I had to euthanise.

Was the other one the Rusty Raymobile????

[bmcecosse]

If the vacuum advance unit is not working - the engine IS very 'flat' and unresponsive - been there done that. Running along on part throttle - and then flooring the pedal - the pick-up is slow, at least at first. When the vac advance is working, on part throttle the advance is pulled well up, and on flooring the throttle it stays up for a second or too - in fact at this stage my engine pinks lightly, and using this advanced timing - the engine accelerates away. Of course - if the static timing has been wound forward to compensate for the failed vac unit - this effect won't be so prominent - but the engine is then likely to be difficult to start especially on cold mornings....

[rayofleamington]

When the vac advance is working, on part throttle the advance is pulled well up, and on flooring the throttle it stays up for a second or too - in fact at this stage my engine pinks lightly,

Sounds like your vac advance is sluggish/faulty then as it should be a bit quicker than that and you would get less pinking Roy.

Was the other one the Rusty Raymobile????

No - One was a floorless 62 4dr saloon and the other was a 71 Austin LCV with rotten chassis, rotten cab and rotten load bay roof. This was back in the mid 90's. These days the rotten van would have had a resale value.