Morris Minor Owners Club

At long last and despite my best efforts to sabotage the project my newley rebuilt engine is in and running. OK got a very very slight leak from the rear of the sump but everything else appears great BUT
The engine ticks over quite lumpily if thats the right word. Borrowed all the gear to set up the engine including a 'colour tune' and strobe light.
New Dis Cap, points, condenser, plugs. Plugs confirm that the mixture is correct after setting with the colour tune. Its not a permanent misfire but definately hesitates on idle. I've connected a revecounter multimeter thing which goes to the low tension connection on the coil and you can see it flick repeatedly but not regularly. This shows up with the strobe light as it makes the timing move as the revs drop. Ive set it to 1.5 deg before top as per the book but it does vary a bit

Any suggestions please

Hand back the colour tune and strobe! Both a waste of time. I'm assuming the engine is in good order, with good even compressions (compression check would be good!) and the cylinder head has been torqued down again and the valve gaps have been set correctly. Also assuming the vacuum advance is working as it should - and is connected! Adjust the ignition timing while the engine is idling, 'by ear' until it seems to give the nicest idle, then adjust the mixture to also give the nicest idle (and reset idle speed as you go) - and then test it by using the little 'lift' pin to raise the carb piston about 1/8". If revs increase then it's too rich, if revs drop/falter then it's too weak. If nothing much happens - it's just right. Then road test the car - and listen for pinking. If none -advance slightly until you DO hear pinking, and then retard slightly. After a good run of at least 10 miles - switch off without any 'city' driving, and pull out a spark plug to see the colour. Should be light beige. If white = too weak, and if brown/black = too rich.

Hello BMCE,

"Hand back the colour tune and strobe! Both a waste of time"

A little dismissive, if I may say so. Like all things if used correctly and with some understanding they are both very useful.

Pb, where did you get the 1.5 degrees, that is too retarded, especially if you didn't disconnect the vacuum advance when using the strobe. Depending on the idle speed, it's not unusual to see the timing retard with a drop in revs. Some distributors start their mechanical advance at quite a low speed .

Alec

Roy you old Luddite you
Vizard "The colortune is one of those devices which is so basic it cannot give the wrong answer" "This device will allow very accurate setting of the mixture" "sufficiently accurate that it will pick up the mixture bias between cylinders"

By the way thanks for the advice about the AAA needle it seems near perfect

The SU comes with an excellent idling mixture test device - the lift pin! No need for colour tune - and Vizard doesn't mention it in my A series book! You confirm my point about the strobe Alec - NO ONE 'knows' what ignition setting to use - therefore the 'strobe' is useless. It must be set up initially by 'ear' - and then by detecting pinking.
And -when was I ever anything but 'dismissive' of useless things!!

Tuning the A-Series Engine by David Vizard - 3rd Edition - Chapter 7, Part 2 - Tuning SU Carbs - Page92

Hello BMCE,

both the colour tune and the strobe can be used at other than idle, the latter will also tell you how much scatter there is. I regularly use my strobe and set the timing to a setting I know works determined by driving the car.

Alec

You risk a big BANG if you run the colour tune at anything over idle! And anyway - it won't tell you anything useful - because the engine won't be under load! I do have a strobe - I was given it as a 21st birthday present - I'm now retired - and it still hasn't been out of the box...........