try the engine with 6 degs advance , if it pinks under heavy load [ ie uphill or full throttle] or runs on after you stop it then go to 3 degs advance .
if this runs ok then leave it as it is and carry on timing it this way .
basically the more advance you use the more power it will make and the cooler it will run , but you need to combine this advance figure against the octane rating of the petrol used.
i think unleaded is 95-97ron but with a 7-1 comp engine you can run it on almost anything as thats a fairly low compression and will run unleaded just fine , but if youre worried about using unleaded and valve recession then buy a fuel additive something like MILLERS VSP or CARPLAN NITROX .
you need higher octane for higher advance settings , but really this only means in high compression [above 9-1 ] and race type engines .
the higher octane rating is for high compression engines to stop them pre igniting and melting pistons . basically lead used to be used to make higher octane , higher octane gives fuel a deadening effect to stop the high comp engines from firing before the piston reaches top dead , ie trying to make engine fire before piston reaches top and then trying to force piston backwards in effect .
youre 1975 distributor is pretty much same as the old one , it may have different advance curve on it but that shouldnt cause you any problems .
what you get when you set the static advance is the engine at a particular revs and advance setting .
as soon as you push throttle and the inlet manifold vaccum drops , this will then pull the advance diaphragm on the distributor and add more advance to the timing , it may add say something like 38degs at
2000rpm .
so for instance at 2000rpm youll have 38degs distributor advance and 6 degs static advance , which gives you 44degs total advance .
this is the point at which the ignition sparks before the piston reaches top dead , so that the fule is ignited at the right time in order to maximise power etc .
the more advance you run , the more likely you are to get "pinking" occurr .
pinking is a problem because it can make the engine "diesel" [like and air rifle if you put oil in chamber] , and very high pressures and temps can occur within the combustion chamber which melt the piston tops or etch/burn them away , and this is not what you want to happen .
so basically if you have a timing light , set the static advance when engine is ticking over to 6degs advance and see how it runs .
if it runs fine , doesnt pink when under load etc and doesnt overheat then you can keep it as it is .
if you find it does pink then back off the advance 3 degs until the time comes it does run ok .
you also need to set the dwell angle but this will be shown in the manual and is in effect the same range for all the 4cyl engines .
you could do with a gunsons dwell meter and a good strobe light , it will pay for itself time after time .
there is probably a hex nut sticking out the side of dizzy for adjusting the dwell angle of the points while engine is running , if not youll have to set the points gap using feeler gauges and then check the dwell , and adjust gap as necessary in order to get correct dwell angle .
the tuning needs to be set at whatever the handbook says idle revs should be , then adjust the advance and set/check dwell angle, and adjust either as reqd until correct values are for both .
the gunsons autoranger dwell/tachometer can be used to set revs , dwell etc , 58 quid approx .
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hope this helps you .