ignition advance curve 25d6

[saltiga]

I have fitted an electronic distributor brand 123, with vacuum advance, I have tried to find the Lucas advance curve for the 25d6 original distributor with no luck so far. In the healey manual it states the advance is 35 deg. at 6400rpm , as the red line is around the 5500rpm I am very reluctant to rev the engine to 6400 . So the advance curve can tell me, say, what the advance will be at 4000rpm, a much safer limit, also how often would a driver sustain revs above this on the open road, Also on reading the advanced search section , have found conflicting advance set numbers, eg. some say no8, some 5 one said f. I feel the only way to check this would be to check the 123 against the original and safe rev range and adjust accordingly . can any one help here? Saltiga

 

[DerekJ]

What 'Healey manual' is that? The 3000's were redlined at 5200 and max advance occurs well before that.

 

[saltiga]

Its a green covered manual. Austin Healey 100/6 ,3000,p/n akd1178H The British corporation limited, BMC service division , Cowley , oxford , England. Mk111, maximum advance 34-38 deg. at 6400 r.p.m.(crankshaft). I have tried to send copy of the page but meet with failure. IF its before 5200 that fine, if I can get onto an advance curve all my problems will be solved, My rev counter has an orange warning section at around 5200 then a red line section starting about 5650. Is this the norm or is it a funny one? saltiga

 

[HealeyRick]

Try contacting Jeff Schlemmer atAdvanced Distributors: https://advanceddistributors.com/wordpress16/ He's an acknowledged expert at setting up Lucas distributors and can probably help you out.

 

[EV2239]

You need about 10-12degrees btdc at tickover, about 25 at 2000 and 35 degrees from 3000 up. Start with this setting and if the car lacks urged at 2000, try another 5 degrees of advance.

People make all this much too complicated, a Google search might produce the original Lucas advance curve.

If you use a sports cam that makes ticking over difficult, you might need more than 15degrees btdc at tickover, but still no more at full advance.

Ive found over the years that if the timing is right at tickover and full advance, but doesn't pull well from 1-3000, it needs more advance in that region, but not further up. If you have too much advance early on the engine will not be as smooth as it should be.

 

[saltiga]

Thanks for the info. I am a little confused with the timing, so many different advance settings. In my manual it says 15deg. at 600 r.p.m.strobscapic. with a 10deg static setting, there is no mention of disconnecting the vacuum . so I assume its left connected, many say disconnect the vacuum to do this, I assume at these revs the vacuum plays little part in the advance. as I have fitted an electronic 123 distributor the 10deg static and 15 deg stobscapic has been done with the vacuum disconnected , if left connected it goes way over the 15 deg. I have been told by a mechanic to leave the vacuum disconnected. This I don't have a problem with if the advance meets the or goes close to the original distributors advance curve. I will try EV2239's suggested advance figures. A google search has not given me an advance curve, , what I have found is only confusing the issue as they all are different. Saltiga

 

[EV2239]

Strobe with vacuum disconnected. Make sure everything is set by the book and the car is ticking over at 650-850 rpm. It should pull well from just over 1000 rpm in top and even better at around 2000 and then pull strongly on up to somewhere past 5000 if it's a BJ8 and 500 less if it's an earlier car.

 

[bdcvg]

Its a green covered manual. Austin Healey 100/6 ,3000,p/n akd1178H The British corporation limited, BMC service division , Cowley , oxford , England. Mk111, maximum advance 34-38 deg. at 6400 r.p.m.(crankshaft). I have tried to send copy of the page but meet with failure. IF its before 5200 that fine, if I can get onto an advance curve all my problems will be solved, My rev counter has an orange warning section at around 5200 then a red line section starting about 5650. Is this the norm or is it a funny one? saltiga

z

 

[EV2239]

It's likely that BMC would have had a machine to measure the advance curve of the distributor they were testing. Back in the sixties in the UK, I'm guessing strobes were rare and that the timing was set statically once the distributor had been tested off the car.

The advance curve I've suggested is based on memory of one I remember from a BMC Healey book. I've googled and not found it, but I'm sure it is right.

FWIW the pre BJ8 cars don't make much power beyond 4500 and don't really like to be revved past the red line. It's an old engine, so be kind.

 

[Airwave]

Hi saltiga

May I ask you kindly which curve you're finally using now with your ignition 123.

I have a phase II BJ8. My 123 ignition is working for + and - grounded vehicles as I changed mine to -. Initially we set up curve "f". But above 2000 rpm i had a lot of misfire interrupts, though i change the curve to "0" (basic setting). I also rotated the 123 ignition unit a bit and i fixed it just before engine shaking. Basically the misfire interrupts got eliminated, unfortunately at approx. 2500 rpm in 2nd, 3rd and 4th gear I can still state some (at constant speed not accelerating). I think as next i will try / test other curves as I do not believe the source is something else.
Many thanks in advance airwave

 

[andrea]

Hi saltiga

May I ask you kindly which curve you're finally using now with your ignition 123.

I have a phase II BJ8. My 123 ignition is working for + and - grounded vehicles as I changed mine to -. Initially we set up curve "f".

My only problem with the 123 distributor is the necessity to remove, to control the the set up, i also have this distributor on my 100/6
with "fast road cam" -more than 6000 miles from the return on the road-SHELL Full Synt 10W60 lube from the re-bird
I remember (not sure, due the age) that I have "B" curve, set up, very good for me, occasionally my rpm exceeds the 6000, no problems occur,
but a rev limiter can be added