Now running rich

[Peetee]

Quick question. Would you expect an engine that ran fine to then run rich after a cylinder head skim?

[bmcecosse]

How much 'head skim' ? - and what else was done (valves ground in ?) - but basically - if it's been apart at all then it will need setting up again.

[Peetee]

50 thou.
The engine had been set up properly on a rolling road and was running well, but power was not up to spec for a A+ 1275 and it was noted that compression was low.
Now it's exhaust is dark and sooty and idle is a bit low and lumpy.

[bmcecosse]

It's been set-up SINCE the head was skimmed 50 thou - or before ?? To set the ignition (after checking it's all working as it should - including the vacuum advance) - advance it till it pinks - then retard very slightly so it's 'not quite' pinking. Set the carb for best idle - then check the plugs after a hard run to see what colour - switch off at speed and drift to a halt . A standard 1275 A+ is not particularly powerful - what size carb does it have - and what exhaust ??

[Peetee]

Rolling road was before the head skim. Spec is 1275A+, alloy inlet,3 branch and large bore exhaust, HIF44, combustion chambers and valve bosses have been relieved.

[bmcecosse]

Just set it up manually then - no need for a 'rolling road' for such a simple engine. Possibly good for ~60 maybe 65 bhp. What's the compression figures now ? The camshaft and small valve cylinder head being the limiting factors. Put in an MG Metro cam and the large inlet valve head (with basic Vizard mods) and would be good for ~ 75 bhp.

[Peetee]

So what is the tuning procedure with an electronic dizzy please?

[MarkyB]

Same difference,"advance it till it pinks - then retard very slightly so it's 'not quite' pinking"

[Mogwai]

If the needle was optimised for the engine before the head modification it may be slightly out now.
Ignition timing procedure for the electronic dizzy is the same as a points one (as you used the same rr as me they may have set it for maximum advance of about 32° btdc somewhere between 2500 3000 rpm)

[bmcecosse]

Did they do anything to the needle at the rolling road session ????? Is it a standard needle now in the carb - if so - do you know what needle it is ?

[Peetee]

So looking down on the dizzy, is advance a turn clockwise or anticlockwise?

[bmcecosse]

Clockwise! Only a tiny amount - then road test.