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Another timing curiosity...

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Hello,

So I am looking for a little help and an answer to my question. I am trying to set up a new to me 73 2002 with dual dcoe 40s.

I can see that timing is set (25btdc) at 1500rpm for carbs and 2500 for tii and this is whee I get confused. Is there difference because of distributor vac advance vs mechanical advance? IF my carb'd 2002 has a mechanical dist from a tii do I set -25deg at 2500 rpm or at 1500?

Thanks,

Matthew

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1,500 rpm

and if there is a vacuum advance unit on

it's side, disconnect and plug that hose while

making your timing check

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No vac on this distributor, as I mentioned it is from a tii and has mechanical advance...

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I think it should be @2500 as well (at least more than 1500).

Here's some advance curves for Bosch distributors (found this on web, not my own creation). 25deg at 2500 falls within the range.

distributor_curves_183_zps95eb8d01.jpg

Byas[/img]

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2,500 rpm only if you have a tii

DISTRIBUTOR!

If you set a tii distributor at 1500, it'll be too advanced at 2500.

And the whole curve will be too far advanced, too.

The mechanical- only curve has more advance in the weights, since there

is no vacuum advance to add its two cents and 15 degrees.

Now, having said that, you'll probably find that the DCOE's might not like

quite as much advance as the tii did, simply because the tii did such a good

job at fuel distribution. But you might end up pulling 2-4 degrees at most.

The real number I can give you is 36 degrees of total advance at

4500+

Yep, wound way out. That was a totally safe number with any engine

combination I put together under 12:1 compression.

Others have very similar numbers to match.

hth.

t

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here are jpegs of the ignition timing data from the blue book as well as a link to a chart showing distributors with similar advance curves which can help correlate superceeded distributors to the data from the blue book.

A few conversations regarding ignition timing with some tuners has also led me to a similar timing suggestion which Toby gave.

http://www.bmw2002faq.com/index2.php?option=com_forum&Itemid=50&page=download&id=63688&sid=ec789c50cd78d05a0afd1cdcdc074b60

post-19295-13667669861195_thumb.jpg

post-19295-1366766986659_thumb.jpg

post-19295-13667669871242_thumb.jpg

post-19295-13667669875535_thumb.jpg

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2,500 rpm only if you have a tii

DISTRIBUTOR!

If you set a tii distributor at 1500, it'll be too advanced at 2500.

And the whole curve will be too far advanced, too.

The mechanical- only curve has more advance in the weights, since there

is no vacuum advance to add its two cents and 15 degrees.

Now, having said that, you'll probably find that the DCOE's might not like

quite as much advance as the tii did, simply because the tii did such a good

job at fuel distribution. But you might end up pulling 2-4 degrees at most.

The real number I can give you is 36 degrees of total advance at

4500+

Yep, wound way out. That was a totally safe number with any engine

combination I put together under 12:1 compression.

Others have very similar numbers to match.

hth.

t

Confirm on 36* total. +-2*

Since no one actually "recurves" their distributors any more or adjusts the weights on the springs, what a tii dist did in 1970 probably ain't what it's doing now. At worst, set total advance, and see what it is at idle and find something that works in between. Or spin your dist up on a recurve machine and let someone map it and set it.

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this old skol Sun distributor test bench will set you free.

if you had one of these you could rule the World!!

sun_620_640.jpg

and new testers are available today

d14_with_lines-250x250.jpg

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I always wanted to build something like that, just for fun...

t

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Based on advice from Jeff Ireland, I set my timing using the maximum advance method rather than the ball. He recommends 33 deg at about 3200 rpm as a guideline for street engine. This on a 9.3 CR motor, replacement mech. advance dist. and twin 40 webbers. Drive-ability was dramatically improved. No pinging, smooth transition.

I also transposed timing marks (25 and 35 deg) to the front pulley which is easier to see (if you have a front timing peg).

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2,500 rpm only if you have a tii

DISTRIBUTOR!

If you set a tii distributor at 1500, it'll be too advanced at 2500.

And the whole curve will be too far advanced, too.

The mechanical- only curve has more advance in the weights, since there

is no vacuum advance to add its two cents and 15 degrees.

Now, having said that, you'll probably find that the DCOE's might not like

quite as much advance as the tii did, simply because the tii did such a good

job at fuel distribution. But you might end up pulling 2-4 degrees at most.

The real number I can give you is 36 degrees of total advance at

4500+

Yep, wound way out. That was a totally safe number with any engine

combination I put together under 12:1 compression.

Others have very similar numbers to match.

hth.

t

Confirm on 36* total. +-2*

Since no one actually "recurves" their distributors any more or adjusts the weights on the springs, what a tii dist did in 1970 probably ain't what it's doing now. At worst, set total advance, and see what it is at idle and find something that works in between. Or spin your dist up on a recurve machine and let someone map it and set it.

I'm also at 36* total (though, on a megajolt). m10s sure do love their advance!

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maximum advance on a tii dist (jfd4 0231188002) occurs at about 4k rpm?

Should I set 32deg at 4k or 36 at 4500rpm?

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