7 replies to this topic

[cad_man2]

Model:City
Year:1982

Hi , I've recently purchased a 1982 Mini City for my Son to drive. The service history of the car is not well documented, so we thought it would be a good idea to start from basics... new plugs, points, filters, oil etc.... We fitted new plugs & points and carefully checked spark gaps on plugs and gap/dwell on points. Engine starts fine and runs OK with some choke at about 1300rpm, but gets very lumpy when choke is off (even when engine is warm). When driving the car it seems to lack power (Ne plugs & points have so far made things worse!).

The question is what should I do next, I guess the timing probably needs to be set (I have a strobe) - but I'm unsure exactly how this should be done, also the idle speed and mixture settings probably need to be adjusted too (think it's running a bit 'rich' as old plugs were covered in carbon/soot) but I'm not sure how to do this either.

What is the 'normal' sequence of events you'd use is it plugs/points/timing/idle speed/mixture or is there a better way? Is there usually some interaction between all these settings - like if I change teh 'mix' will that effect idle speed, timing etc and will these need to be re-tweaked?

Sorry for these basic questions but as you can guess I'm a novice and have got totally confused by the Heynes manual!
:

[Big_Adam]

If it runs aright with the choke then I want you to try this.

Drive with the choke out. Just pull it all the way and go for a spin. If the cat runs much better then, the problem lies in the fuel mixture.

If you can't drive it (wheels missing, sorn, ETC) then look at the carb from the engine bay, stick your head over the top, left hand side underneith it there is a small spurn pin called a lift pin. While the engine is running lift the pin/push the pin up (into the carb) and see if the engine dies/revs. If it dies then it's mixture is too weak. If it revs up then it's too high. I'm guessing it's low though.

So check the mix. Either use the lift pin, try driving with the choke out (not for long though) or get the mix set on a rolling road. Or be very flash and do it by ear, an ability I've lost.

[Dan]

The Haynes manual gives a very good description of how to perform a service and basic tune of the car. Older manuals do anyway, I haven't seen the latest edition. Regarding the lift pin, the engine should slow but not stop altogether when it is lifted.

[bmcecosse]

To set the timing - just gently move the dizzy back and forth until you get the 'best' idle. Similarly for mixture - try it weak then rich - back and forth and settle at best idle. You can of course use the 'lift pin' - nut only lift it very slightly to get a slowing or speeding up effect - if you lift it right up the engine always stalls! Best to check the valve gaps - and would be a good idea to get a compression check to determine general engine condition.

[cad_man2]

Thanks all for your suggestions... pleased to say that engine is running great now.

Wjhat we did was -

1. Changed points & set point gap, then tweaked for correct dwell
2. Used strobe to set timing by rotating distributor
3. 'Fiddled' with idle speed control & mixture settings on carb until engine appeared to be running correctly

Just wondering whether there is a better way of doing item 3 as it seems a bit 'hit & miss' ? We used a tacho for idle speed adjustment - is there a more scientific way of setting the mixture correctly?

Thanks again!

by the way I couldn't find the 'lift pin' you mentioned, is it possible I've got a different type of carb?

[Wil_h]

The fuelling requirements for the engine is controlled by the profile of the needle. Assuming that the needle is the correct profile, the mixture screw is just for setting the idle mixture. Because of the way the carb works it of course affects the mixture throughout the rev-range.

The only way to really get the mixture right is to fit a lambda gauge and sensor, or take it to a rolling road.

[cambiker71]

Later carbs had no lift pin, the same effect can be applied by undoing the dashpot top and lifting it slightly but this is still a bit hit and miss, best to ask a mini friendly garage to check it on a gas analyser once you have the points and timing set correctly. (As you've already mentioned)

[bmcecosse]

If it's running fine now - just take it for a good run, and then have a look at the spark plugs. They should be light beige colour if mixture is correct. If black = rich, if white = weak.