Had my early cast iron Bosch redone by Ed Fall a few years back. I was checking the advance today and when I set it at 5 BTDC (a few mm to the right of Z1) I get 25-30 total advance. Doesn't go to 35.
How much total advance should be in an early cast iron Bosch?
Car runs good....but don't want to miss any top end power because of too little advance.
Oh, by the way, I stink like exhaust big time after dinking with this all night and my wife is not pleased! Haha!!
http://forums.pelicanparts.com/911-e...ed-engine.html
I don't think you should set the idle advance to five degrees-- that will make it idle too fast. If it's really idling at 5 degrees advanced, I wonder what your idle AFR is.
Remember that the springs and weights only have a certain range, so you add the static timing to the distributor timing to get all-in. If you are using 5 to start with, that suggests that there is only 20-25 degrees of advance in the distributor range.
Mike, as you can see from the attached graph, my cast-iron develops about 30 degrees all in. http://forums.pelicanparts.com/911-e...tributors.html That is starting from zero. So there should be at least 30 degrees of advance in the distributor, more as it wears.
Did you lube it up before you installed it? I wonder if a weight is sticking?
1966 911 #304065 Irischgruen
I saw something where PMO recommends setting cars with Webers to 5 degrees advances for the best idle. I think factory setting is right at Z1. Yes I believe I am getting only around 20 degrees advance in the distributor....Ed did send me a graph showing the full 35 degrees of advance. Yes I've taken it out and looked it over and lubed it.
I'll contact him and see what we can do here. Don't want to lose any power power power!
No kidding Mike with only 140 ponies on tap you want to make sure they all show up for work when you get on the loud pedal!
Yeah, if I set to anything other than TDC the thing ends up idling at 2000 rpm and emits a backfire when you shut it off that will bring the Department of Environmental Conservation around to see who's poaching.
1966 911 #304065 Irischgruen
Mine seems to idle pretty good a little advanced and no backfiring (luckily). And in my past car experience I know that you usually want to set timing at full advance and then let the idle advance be kind of secondary. But in this case it just seems I'm being short changed about 10-15 degrees and it can be "felt" when accelerating. When it gets fixed I will know, because the car will have a little more "oomph".
I was thinking a "load" on the engine may help with the advance...but then I remembered that only applies to vaccuum advances, not ones that are totally mechanical like ours.
John the combination of the backfiring and also revving a noisy 911 engine to 6K to check full advance makes neighbors love us. Especially done late at night.
The early Bosch dizzys suffer from weak springs. If you cannot get to the advance you need it usually means that the advance is starting at an rpm range below your idle setting. The only way to do this is to disassemble the distributor and reestablish the spring tension.
Aaron Burnham
Burnham Performance
1071 Avenida Acaso ste D.
Camarillo, Ca. 93012
805-240-6931
_________________________
Aaron thanks, that makes a lot of sense . The springs may be weak or loose. I noticed the idle/advance takes a second to drop back down after hitting the gas also, so I think the springs may be the culprit. I did make sure initial idle is at 900 RPM also. Dwell is right at 38-40 degrees.
Ed Fall emailed me back a few days ago, still need to call him.
Aaron, are the springs available to purchase? The springs Ed used when he rebuilt it a year or two back look new to me.....
Depends on the model. Ed may have used 356 springs if your distributor has the same design. If your distributor is in good shape, all that it needs is an adjustment. Your springs readjusted would last as long as new springs. Do not attempt to adjust the springs by bending arms as this will alter total advance.
Aaron Burnham
Burnham Performance
1071 Avenida Acaso ste D.
Camarillo, Ca. 93012
805-240-6931
_________________________
Mine is a 12/65 early cash iron Bosch. Nope, I would never attempt to bend the spring arms or adjust the springs, I don't have a Sun. He may have checked total advance from 0 RPM starting point and not 900 RPM I am thinking. I'll report back after I talk to him.
Unlikely, what does the printout he included with your distributor show? Anyway, total advance is total advance, it doesn't matter where it starts coming in (for purposes of measuring total advance).
When the springs get weak you end up with MORE total advance not less. That's why old cast iron distributors give you a high idle and backfires-- it's because the distributor advance range is like 45 degrees, so you set the top end to be 35 at 6000 rpm and you end up with 10 degrees of advance at idle, too much. You have the opposite problem.
1966 911 #304065 Irischgruen
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