22 replies to this topic

[Ginge620]

18-20 degrees at idle is about same as my 1293 with MD266. Sound a lot but with any less advance it does not idle as smoothly.
 
But to get this I am using about 12-14 deg static advance with very weak primary advance spring in the distributor. And this distributor has 10x2=20 deg of mechanical advance which gives me a maximum of 32-24 deg advance from about 3,500rpm.
 
Would recommend checking your static advance and amount of mechanical advance. There is a number stamped on the advance stop plate in the distributor, should typically be 10 or 12 but can be anything from 7 to 17 depending on the provenance of the distributor. Multiply this number by two to get total mechanical advance in crank degrees, then add static timing to give total advance in crank degrees.
 
If you're over 35 total advance then I would be cautious about using this enthusiastically until you get it set up on rolling road.

There is an 8 stamped on one of the weights. So 8x2 -> 16 + 20 means that it at 36 degrees total. I best retard it then?
Also the springs look different. One thicker/heavy the other thinner/lighted, I imagine that how you get an advance curve rather than straight line ratio?

Edited by Ginge620, 22 August 2015 - 06:09 PM.

[carbon]

Primary spring should be under slight tension, the secondary spring is either same strength as primary, often heavier (thicker wire).

 

The secondary often has bit of slack so this spring only kicks in after a certain amount of mechanical advance is reached, and slows up the rate of the advance curve.

Edited by carbon, 23 August 2015 - 04:16 PM.

[Ginge620]

Primary spring should be under slight tension, the secondary spring is either same strength as primary, often heavier (thicker wire).

 

The secondary often has bit of slack so this spring only kicks in after a certain amount of mechanical advance is reached, and slows up the rate of the advance curve.

Interesting. Neither of the springs are under tension. Would this mean that the total mechanical advance limited due to the distributor always being slightly advanced to start with?

[eean]

I'm running a reprofiled cam (266) in my 1275 midget and fitted a 5° offset key to the timing chain pulley, do you not need to do this or have you got adjustable timing gear?

[Ginge620]

I'm running a reprofiled cam (266) in my 1275 midget and fitted a 5° offset key to the timing chain pulley, do you not need to do this or have you got adjustable timing gear?

I check checked the timing and everything appeared to be in spec. I have a lightend none adjustable duplex gear set.

[KernowCooper]

Were talking ignition timing and advance curves, cam timing would not normally be readjusted once set up on the build

[eean]

Yeh I know that cam timing wouldn't be adjusted once set, just wondered if it would affect setting the ignition

[carbon]

 

Primary spring should be under slight tension, the secondary spring is either same strength as primary, often heavier (thicker wire).

 

The secondary often has bit of slack so this spring only kicks in after a certain amount of mechanical advance is reached, and slows up the rate of the advance curve.

Interesting. Neither of the springs are under tension. Would this mean that the total mechanical advance limited due to the distributor always being slightly advanced to start with?

 

Yes, if both springs are sleck then as soon as it spins even at 200rpm the mechanical advance will take up any slack. So effectively the total mechanical advance in the dizzy will be reduced by that play in the 'slack'.

 

I think it may also mean that any measurement you make of the static ignition timing could be fairly inaccurate.

 

Advance springs can be tweaked slightly to increase or reduce tension.