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Author Topic: Please help me figure out this off-idle stumble!!!!  (Read 15970 times)
93reefblueGT
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« Reply #15 on: August 17, 2015, 01:56:12 am »

Once you go lock you never go bock..... needs more timing, i also have a holley 750 double pumper mechanical secondary that 1 year old for sale.
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blackgt85
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« Reply #16 on: August 17, 2015, 02:34:59 pm »

Have you verified where top dead center is and marked your balancer?
Here's a link to distributor recurve
http://www.reincarnation-automotive.com/Duraspark_distributor_recurve_instructions_index.html

Yes, TDC was verified and timing tape is on the balancer so I get nice readings.  Everything is all good there. 

Thank you for the link.  I did some searching last night because I thought I remembered seeing something like that years ago.  The info contained in that site is also used over at http://vb.foureyedpride.com/showthread.php?22229-The-Ultimate-Duraspark-Distributor-Timing-Guide

I am actually kind of surprised I couldn't find anything like that over here.  It would make an excellent sticky. 
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Justin
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« Reply #17 on: August 17, 2015, 03:17:14 pm »

You can't just increase initial timing. As you do, total timing also increases. You will have to modify the mechanical advance arm to limit total timing when you increase the initial.

Have you done anything to the mechanical advance? Different arm? Lighter springs?

And when you increase your timing that much, you will need to reset your idle mixture screws and likely adjust idle speed. I'd expect it to increase vacuum.

Ok, I have done a lot of reading on initial timing, total timing, advance curves, reluctor arms, springs and so on.  I ordered up the spring kit from Mr. Gasket, p/n 925D.  Since I have the day off, I am going to go out in the garage after she gets home to see which arm is in the distributor.  If that needs to be modified, I might need to wait until next weekend to get it welded up.  I am guessing I will probably want to make it equivalent to a 7L, so if needed I can enlarge it, correct?  I appreciate all of the help greatly.  Thank you.
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Justin
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« Reply #18 on: August 17, 2015, 04:55:25 pm »

I am actually kind of surprised I couldn't find anything like that over here.  It would make an excellent sticky. 

I normally just give people that same link.

I've got some pics of other Duraspark mods but haven't had time to put anything decent together. Brazed and modified advance arms, vacuum advance lockout, and a few variations of mechanical advance lockout. I'm also working on a setup to allow for phasing the rotor with nothing more than a small wrench.
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Doing more with less, or something like that.
http://sbftech.com/index.php/topic,20009.0.html

Quote from: Monte Smith
Bottom line, if it was the hot ticket, the fast guys would do it.............they don't

You might need some Titanium rods and a flow bench!  LMAO on floor

I honestly don't get it.

I'm sweating, my heart is racing, my clutch foot is twichin', and my right arm punched the computer screen doing an involentary 2-3 shift while reading all that. 
blackgt85
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« Reply #19 on: August 31, 2015, 02:35:39 am »


I normally just give people that same link.

I've got some pics of other Duraspark mods but haven't had time to put anything decent together. Brazed and modified advance arms, vacuum advance lockout, and a few variations of mechanical advance lockout. I'm also working on a setup to allow for phasing the rotor with nothing more than a small wrench.

Explain this vacuum advance lockout please.  My VA canister isn't adjustable, and I don't know if I want to spend the money on the adjustable canister from Crane...  From what I have read, I will want the VA, but if not needed, I don't mind.  Aren't MSD distributors just a mechanical advance style?  Thanks.
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Justin
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« Reply #20 on: August 31, 2015, 08:19:16 pm »

Explain this vacuum advance lockout please.  My VA canister isn't adjustable, and I don't know if I want to spend the money on the adjustable canister from Crane...  From what I have read, I will want the VA, but if not needed, I don't mind.  Aren't MSD distributors just a mechanical advance style?  Thanks.

It is nothing more than the arm from a broken vacuum canister, thats riveted to a small aluminum bracket. It attaches inside the distributor where the vacuum advance did, and the bracket is held in place by the two screws that held the canister on.

For a engine like that, I wouldn't think that you would want vacuum advance. More so, I don't think it would want much advance at all.

MSD distributors are available with mechanical advance and with or without vacuum advance. They can also be locked out for no advance at all.
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Doing more with less, or something like that.
http://sbftech.com/index.php/topic,20009.0.html

Quote from: Monte Smith
Bottom line, if it was the hot ticket, the fast guys would do it.............they don't

You might need some Titanium rods and a flow bench!  LMAO on floor

I honestly don't get it.

I'm sweating, my heart is racing, my clutch foot is twichin', and my right arm punched the computer screen doing an involentary 2-3 shift while reading all that. 
blackgt85
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« Reply #21 on: September 01, 2015, 12:56:22 am »

So far the mods to the timing have been welding the reluctor arm (or whatever it is called) to both 7L (.332") and 8L (.358").  I have put it on the 7L to see how it acts with 22-24* Initial timing.  I also purchased the Mr. Gasket 925D spring kit, and swapped out the heavier of the 2 original springs with a lighter 925D spring. 

I won't have a chance to play with it again until this coming weekend to see how it reacts and how much vacuum I can get it to pull.  I will also have an AEM wideband showing up tomorrow, so that will be getting installed this weekend to help out with monitoring the A/F ratio...  The weekend after is the 3,500 stall and Silverfox VB install weekend...  Wink 
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Justin
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« Reply #22 on: September 11, 2015, 08:10:52 pm »

Well, I was out in the garage today playing around with the car now that it is back together again.  The reluctor arm is at the "7L" position, initial timing is at 22*, and at 2800rpm the total is all in at 36*.  It seems to like it at that spot so far.  I have readjusted the idle mixture screws to get the most vacuum and I am now pulling 13-14" at idle (1000rpm).  I do not have the vacuum advance hooked up at all, and might just leave it disconnected when I take it out for the test run tomorrow. 

However, I was still getting the nasty spitting and sputtering (or coughing), and backfiring when snapping the throttle open quickly.  I took another peak at my Holley tuning DVD and after watching, checked out the adjustment of my accelerator pump.  It was tight, and I could not get the .015" feeler gauge in between, and when I did, with the throttle wide open, did not make a difference in movement of the arm when pulled out.  I loosened up the screw and nut until I was able to see the arm come up ever so slightly when pulling the feeler gauge out, and the coughing seems to be gone.  It seems to be a bit more snappier when cracking the throttle.  I guess we shall see what the test drive brings tomorrow!

Thank you to everyone for all of the help so far.  It has not gone unappreciated!
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Justin
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« Reply #23 on: September 11, 2015, 11:21:29 pm »

I set them to where the arm first contacts the lever, but without slack. That ensures that the full pump shot is available. With a vacuum secondary, it may be necessary to convert to a 50cc pump to get enough fuel for acceleration.
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Doing more with less, or something like that.
http://sbftech.com/index.php/topic,20009.0.html

Quote from: Monte Smith
Bottom line, if it was the hot ticket, the fast guys would do it.............they don't

You might need some Titanium rods and a flow bench!  LMAO on floor

I honestly don't get it.

I'm sweating, my heart is racing, my clutch foot is twichin', and my right arm punched the computer screen doing an involentary 2-3 shift while reading all that. 
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