Help! Ignition Timing 2.25 Petrol

Recently been having running trouble with a IIa 2.25.

Check7.0:1 engine

75 RON 3deg Before 80-85 R7.0:1 or 8.0:1 engine 75 RON TDC 80-85 RON 3deg Before 90-95 R7.0:1 engine 75 RON TDC 80-85 RON 3deg Before

8.0:1 engine

80-85 RON 3deg AFTER 90 RON TDC

Considering all these engines are the same, use supposedly the same distributor, and have the same valve timing, why the hell is there so much difference? Some of the figures i can accept as being "optimal" and varying slightly (vis 3deg or 6deg for 85RON) but how come the setting for a IIa with 90RON is 6degrees before, but for a III with

90RON it is TDC?

To complicate matters further I have a 1965 IIa engine which has a Lucas 45D distributor fitted, from a 1975 vintage engine. Now what do i set it to?

Cheers

Alex

Reply to
Alex
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You could do it the old way get the engine nicely warm slack off the pinch bolt and slowly adjust for best revs then tweak the throttle to make certain she doesnt bog down if alls well nip up the pinch bolt and have a test run if she pinks retard the ignition a couple of degrees and check again. I admit its not a book accurate way to do the job but if you are running non-standard equipment or there is wear in the dizzy you are likely to get the best result that way . Derek

Reply to
Derek

The engnes are very similar, but the disrtibutors are not necesserily (Early Lucas, Late Lucas & Ducellier, plus any aftermarket ones fitted).

Setting it to TDC will get it running, after that ensure the points gap is correct and move the distributor until it runs nicely!

Richard

Reply to
beamendsltd

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 .

Reply to
m0bcg

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