1977

Member

• Apr 4, 2017

• #1

Hi there
This is a simple one I think. I'm currently getting 6.2 mpg out of my series 3 with overdrive, its been like this for a year now. Before a like for like engine change I had 35-40 mpg!!!! but with the same carb. I have now had to rebuild this engine and there is no real improvement in fuel consumption. The mixture screw is only half a turn from fully tight and it only comfortably idles at 1100 rpm. The garage took the emission control off as they didn't think I needed it. Is it time to rectify another mistake by the garage by buying a new carb?

 

tottot

Well-Known Member

• Apr 4, 2017

• #2

Something is/was wrong either way. low to middle 20's is good for a two and a quarter petrol.Take the plugs out and let us know the colour they are.

 

1977

Member

• Apr 4, 2017

• #3

they are not thick with soot but they are slightly black.

 

1977

Member

• Apr 4, 2017

• #4

they are not thick with soot but they are slightly black.

 

doodle bug

Well-Known Member

• Apr 4, 2017

• #5

1977 said:

Hi there
This is a simple one I think. I'm currently getting 6.2 mpg out of my series 3 with overdrive, its been like this for a year now. Before a like for like engine change I had 35-40 mpg!!!! but with the same carb. I have now had to rebuild this engine and there is no real improvement in fuel consumption. The mixture screw is only half a turn from fully tight and it only comfortably idles at 1100 rpm. The garage took the emission control off as they didn't think I needed it. Is it time to rectify another mistake by the garage by buying a new carb?

Click to expand...

Time for a new carb !

 

tottot

Well-Known Member

• Apr 4, 2017

• #6

Running rich then, should be a light brown. Turning the screw IN [clockwise ] richens the mixture [many think its the other way] Start at two turns out and go from there.

 

1977

Member

• Apr 4, 2017

• #7

I did run for a fue months like that with it 4 turns or something like that and got roughly the same fuel consumption but ill try it again

 

J

John S

Well-Known Member

• Apr 4, 2017

• #8

You have to establish a baseline position before adjusting. Try googling there's loads of stuff on this. It looks like the carburettor isn't set up both the idle jet and the mixture.

 

tottot

Well-Known Member

• Apr 5, 2017

• #9

Doodle bug may well be right.

 

oxides

Well-Known Member

• Apr 5, 2017

• #10

Playing around with the idle mixture won't fix the problem. First of all make sure the ignition system is working properly and the ignition timing is correct. Are you getting much black smoke out of the exhaust? If so try replacing or rebuilding the carb, watching out for any body warping that just lets fuel pour out of the float chamber into the inlet manifold.