7 replies to this topic

[gdcarpenter]

1990 Japanese Spec Mini Mayfair 1000 with Cooper Conversion.
Lucas Dizzy 65DM4 AUU 1536 2005 #42664A 0398

Finally got my advancable timing light and timing at idle set, but max. advance only 15 degrees at 2,000 RPM, and does not advance beyond that, even at 4,000 RPM.

Pulled distributor and centrifugal weight stamped "16" which I take to be 16 degrees distributor advance, which I understand should equate to 32 degrees C/S advance, or does it??????

Weights and springs look fine and move freely, sprayed some dry lube. Reinstalled and still the same.

Anything I may have missed or not noticed inside distributor, I did not remove the metal disc with vertical arms for trigger as I was not sure how retainer for that is removed, but pulled the shaft out of the housing.

Thinking I should be closer to 25-30 degrees max for my car. Twin 1 14" SU's per Cooper conversion, "Cooper" stamped head so assuming it's one of the 1989 anniversary performance flow heads, CAM 4810.
LCB running through CAT into R40 side exit at the back.

Runs like a champ but hope there's a bit more in her with better max advance.

Thanks.

[Earwax]

Don't forget total timing is idle plus mechanical ( plus vac if setup).  I always set my ALL IN  figure at 5000rpm at say 30 degrees and then see what that correlates to at idle.  ( Note some ignition curves have slower rate of rise and so could still be rising at 4000 , so I check at 5000 to be sure)   On A series 1275 motors that i am familiar with that usually equates to an idle around 10.  I am not familiar with the Jap spec motor , so all of the above may be not applicable. A dizzy cam with 10-13 degrees should be  plenty of advance- if yours does have 16/32 degrees then theoretically you should be more advanced through the rev range rather than retarded-??? 

[gdcarpenter]

Thanks, current 15 degrees at 2,500 RPM is certainly fine, thought the 'Cooper' head could take a little more. Have read where one could file the weight stops to get a tad more advance, keeping in mind every 1 degree of distributor advance is 2 degrees of CS advance.

Just curious when I saw "16" stamped on the weight. Running manifold vacuum advance so at idle 10 degrees BTDC centrifugal and another 15 degrees vacuum when connected, ergo no vac advance at high RPM.

[gazza82]

VAcuum drops when the throttle is open wider .. so vacuum advance would too

[Spider]

That distributor, unless it's been modified isn't for a 998 engine, but for an MG Spec 1275 Engine.

 

The figures you are seeing on test maybe as a result of it being modified to suit the Cooper 998 Spec Engine, but usually, it would be assigned a different number or be noted in some way on the body that it's been modified, especially given the car's original pedigree.

[gdcarpenter]

That's all, yes the vacuum advance is only at idle, and I never thought of the distributor having already been modified but that makes sense.

[nicklouse]

Not just at idle. Read the info on the side of the vac can.

 

then take the fussy out and do some measurements.

[gdcarpenter]

Mini runs fine so this is now a curiosity and want to understand better exercise.

Pulled the dizzy again this AM and with magnifying glass for older eyes found the 'C' clip holding the reluctaor on. It is a 16 degree unit as I placed reluctor at no advance, marked housing, moved the reluctor to full advance and marked housing, and there was 16 degrees between the marks. Still not giving me that, but as I said, Mini runs fine, and 32 degrees advance all inwould likely be too much.

Back up and idle retimed, used vacuum pump to activate vacuum advance unit, pretty much on spec:
80 mm hg (3+ in hg) 200 mm hg (7+ in hg) 8 degrees distributor advance measured 16 degrees C/S advance.
With dizzy plugged into ported vacuum I got total advance around 25 degrees around 4,500 RPM, had previously run manifold vacuum.
Having switched my vacuum advance line from Manifold to Ported vacuum, I teed in a vacuum gauge and ran it into the Mini.

First gear very little vacuum second more, and by third gear, at part throttle 8-10 in hg. I assume there just is not the same CFM of air moving through the engine in lower gears causing the lower ported vacuum readings, Vacuum obviously drops off to zero when the hammer is down or petal is to the metal. This makes sense to give best fuel efficiency and performance at cruising speed, which, with my 3.44:1 final drive, is about 4,000 RPM @about 70 MPH.

So, in anothe post I explained why I used Manifold vacuum for the advance, I was wrong and stand corrected, ported is the way to go.