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MG MGA - Plugs and Timing

My 1961MGA is running well but a couple of things seem amiss. The plugs are white ( not light brown ) but the exhaust tip ( not the exhaust colour ) is very black with lots of carbon build up.
The carbs seem to be adjusted Ok but I'm curious as to what may be causing this.

Thanks.
DA MacFarlane

Is the timing right?
Graham V

Hi, it hasn’t changed and had been running fine. I’ll check the floats first...seems to be a carb problem..,
DA MacFarlane

unleaded fuel tends to run with a darker tailpipe colour
With the plug colour you might have picked up some old semi stale fuel or some with a touch too much ethanol in it
If you try to run E10 the plugs go white
There's always the chance of fuels getting mixed up at the petrol station
I,d wait till your tank is nearly empty and try it on some fresh fuel then recheck the plugs
Over here they (whoever they are)are allowed to go up to 5% ethanol in ordinary fuel without having to say and if you get some that is older where that 5% eth. has gone off it causes all sorts of starting and running issues

Best to get fuel from the busiest servo you can find, at least you know it's fresh
William Revit

I use premium fuel here but the tailpipe is sooty - not just dark. I noticed today when I was test driving it, the engine would misfire ( flutter) ) for about 2-3 seconds and then smooth out for 4-6 seconds. It continued this cycle all the way home - about 3km. Its been hot ( 28C- 30 C ) most the week and the car definitely does not run as well in the heat. Lastly, it is very hard to start after being stopped for 30 minutes but with the temperature gauge still at ~ 212F.
Time for some forensics! 😄
DA MacFarlane

Sounds familiar
If you get some fuel out of the car and splash it on something smooth- If it doesn't evaporate off as quick as what you think it should and leaves a slimey feeling residue it's gone off---If it evaporates off nice and dry it's normally ok
If it's laced with ethanol and gone off usually the fuel also takes on a slight milky look
William Revit

Hi. I don’t believe that it’s the fuel. This has happened with a few tanks from different gas stations...alll premium fuel with no ethanol. The sputtering is “ rhythmic “ and if the fuel was off,I don’t think that it would react this way.
I’m dud a little test when it was running poorly. I disconnected the linkage and when I lifted the front car the engine accelerated but when I lifted the rear carb - no change. So apparently a lack of ( or sporadic ) feed of fuel to that carb. I’m guessing that the float is dirty or sticking.
DA MacFarlane

Well !

Confirmed the timing, changed the plugs, but ...the carbs were the culprit.

I disconnected the linkage after starting it up this am. It was not quite to running temp but it started and ran rough. When i lifted the throttle on the front carb - vroom . When I lifted the rear carb throttle - blah, sputter, etc. Scott from Drakes British Parts in Kelowna, BC had a unique ( to me anyway ) "trick". I removed the air cleaners, blocked the intake on the rear carb and revved it up to 3500-4000 rpm.

And viola - worked like a charm. I imagine that there was something plugging the carb intermittently.


Runs like a charm again ...

DA MacFarlane

This thread was discussed between 17/08/2018 and 24/08/2018

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