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I have tossed this out at a few sites but as yet I have no solution, perhaps there are some answers here.
OK, here are the specs;
331 stroker 9.1 to 1 cr with 150# cylinder pressure
cam is 220 in and out @.050 with 110 lobe separation
Holley 670 Edel performer heads and RPM manifold.
Crane HI-6 box,LS-91 coil and Street and race distributer Dizzy has 3 vacuum and 9 mechanical advance selections
TDC is verified
I have tried in vain to get this set up to run on mid grade and 87 octane. No combination of initial , vacuum and mechanical setting will work, it either will idle nicely and ping on acceleration or will idle rough and not ping.
Crane tech has not offered any solutions so I guess I'm stuck with hi test.
Using 91-93 with 10% eth. and the distributer vacuum advance set at 0, initial at about 12-15 degrees it idles a bit rough but needs to be there to prevent preignition. The car is not raced, it's a driver. So, the question is what kind of advance curve setting should I use for optimum gas mileage when the cruise RPM is 2000 at 70 MPH.
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Have you plotted the ignition curves? What's your total timing at 2000? Sounds like you might benefit from a slower curve. Maybe try starting with 8-10 degrees initial and 20 degrees total at 2000 rpm(with the vacuum advance still at 0). It's also possible you could be a little lean or have a vacuum leak. All the ignition mods in the world won't cure that.
Last edited by at (7/18/2014 12:36 PM)
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may be a carburetor issue. 9:1 compression with aluminum heads ought to run easily and well on 87 octane fuel.
Last edited by Nasty65 (7/18/2014 2:56 PM)
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What is your idle RPM? I'm guessing you should be able to idle around the 700-900 range.
How any turns open are the idle mixtures screws?
You may need to play with the idle mixture and the idle speed adjustments to get to the "right" place.
I'd play with these first, with initial timing in the 10-15 range. Then I would attack the off idle timing curve.
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Try about 20* initial(maybe even more) and a total of 36* @2000RPM. That is -oh no I used a word I shouldn't have--uming the starter will spin it over when hot.
That LSA and duration likes a lot of initial to clean up the idle.
Have the vacuum advance hooked up to manifold vacuum NOT ported vacuum.
With a pile of initial re-adjust the carb and you should be able to lower the idle screw to get the curb idle down where you need it.
A lot of fellows even go with a fully locked out distrib. butt you are not that radical on the camshaft IMHO.
6sal6
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I am having better results with initial 15 advance and the vacuum disabled and a total of 38 degrees.
I am going to substitute the Crane distributer with the original and see what that combo does.
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Rudi.........was the cam degreed when installed?
6s6
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6sally6 wrote:
Try about 20* initial(maybe even more) and a total of 36* @2000RPM. That is -oh no I used a word I shouldn't have--uming the starter will spin it over when hot.
Have the vacuum advance hooked up to manifold vacuum NOT ported vacuum.6sal6
^
The whole reason I'm installing a PMGR starter is that setting mine to 18* initial running ported vacuum the engine wouldn't turn over cold.
Does that HI-6 CD box have a start/ retard function?
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Is the carb new or in "out of the box" condition? Has it had anything changed or done to it, i.e. jetting etc...? how far out are the idle mixture screws?
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6sally6 wrote:
Try about 20* initial(maybe even more) and a total of 36* @2000RPM. That is -oh no I used a word I shouldn't have--uming the starter will spin it over when hot.
That LSA and duration likes a lot of initial to clean up the idle.
Have the vacuum advance hooked up to manifold vacuum NOT ported vacuum.
With a pile of initial re-adjust the carb and you should be able to lower the idle screw to get the curb idle down where you need it.
A lot of fellows even go with a fully locked out distrib. butt you are not that radical on the camshaft IMHO.
6sal6
WHAT!!!!!! ASSUMING is a naughty word?! Gimme a brake(automotive talk for break!)
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The cam was degree'd.
The carb has been tuned and the air bleed screws are set to max vacuum.
The idle rpm is 7-800 in drive.
There are 9 advance settings to choose from I have the preignition under control, all in at 2000.
I'm working on the idle now.
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