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Old 06-01-2008, 09:45 PM
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help with msd ignition

Hi my name is Jon I have a 70 nova with a 350 in it. just put msd ignition on it and new msd distributor to fix timing problems timing is great now but couldnt fix the problem of it falling on its face off idle when I give it hard throttle. It has an edelbrock 750 on it I know to much but I had a carter 750 before and it ran awesome till the carb just got to crappy. It needs a 600cfm Im sure but if my 750 is fine and not the cause of the problem Ill leave it on there. Please point me in the right direction, thank you.
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Old 06-02-2008, 06:35 AM
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Quote:
Originally Posted by fireman147
Hi my name is Jon I have a 70 nova with a 350 in it. just put msd ignition on it and new msd distributor to fix timing problems timing is great now but couldnt fix the problem of it falling on its face off idle when I give it hard throttle. It has an edelbrock 750 on it I know to much but I had a carter 750 before and it ran awesome till the carb just got to crappy. It needs a 600cfm Im sure but if my 750 is fine and not the cause of the problem Ill leave it on there. Please point me in the right direction, thank you.
I would try a calibration kit for that carb. Give it a little more of a pump shot for starters and maybe some stiffer needle springs to get into power mode a little quicker. First things first. Look down the throat and make sure your accelerator pump is working.
Also, some timing specs would be nice.
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Old 06-02-2008, 06:41 AM
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Did you happen to re-curve the distributor before installation??? I'm pretty sure the come out of the box with heavy springs installed for the mechanical advance.
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Old 06-03-2008, 05:08 PM
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hmmm!!!!!!!!!!

No I didnt recalibrate anything just figured if the 750 before worked fine why not this one. So you think stiffer springs, one guy said they come with stiff ones already, you think perhaps stiffer ones are needed. The accelerator pump is working also I adjusted the lever for more angle to pump more and sooner no defference. Also by saying calibration kit did you mean jet kit with springs and all the goodies? Some one mentioned recurve the distributor yes I did light silver, light blue springs, and blue advance stop bushing. Which causes the curve to start around 1400 rpm and raises to 22 degrees by 3200 rpm and then flattens out till she blows. I really dont think its timeing no matter where my distributor is turned, way advanced or retarded it falls on its face. By advaceing the crap out of the distributor it almost eliminates the falling but barely runs down the road missing really bad. If I put 2 silver springs in the distributor it will start advancing around 800 rpms and be up to 22 degrees but 2800 rpms????? And one last question sorry!! How far should the advace go like I said it goes to 22 degees. I can put in a silver and stop at 25 degrees or a red and stop at 30 degrees. OR a black and only go to 18 degrees. Thank you for any help Im treading water it is very much appreciated!!!!!!!!!!!!!!!!
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Old 06-03-2008, 05:41 PM
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no vacuum advance? and your driving around, on the street? yeah , its gonna suck.

i would set up a ignition system for your proper application, that will give the engine the timming it needs.

at idle you should have 12-16 initail + 15-20 in the can when vacuum pulls. it will crank with 14-16 and pull up to 30ish.

dont try to be fast until you have the engine stable and running right.
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Old 06-03-2008, 06:12 PM
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I have a vacuum advance on the distributor and its hooked up. Are you talking about on the harmonic balancer should be 12-16 advanced from zero, and what do you men 15- 20 in the can??? Man Im either retarded or missing the obvious.
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Old 06-03-2008, 06:34 PM
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I personally would not even be worried about vac advance at this time..(It doesn't do anything at WOT anyway)... You might try one med spring and one lite spring for the mechanical advance with a total timing 30-36 degrees with one lite and one med it should bring it all in around 3000-3500. DO you have any idea what you had the timing set to prior to new distributor? Just curious
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Old 06-04-2008, 07:24 AM
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All carbs are not designed the same. The Edelbrock is supposed to be a clone of the Carter - it isn't. It just looks like an AFB. The primary venturis are totally different with the Carter's usually being much smaller and the secondaries being very big - volumetric efficiancy. Also, that loose set of plates above the secondary throttle plates have different opening timing and lastly, the Edelbrock is easily tunable. One 750 cfm carb is not the same as another and a 750 is way too big for anything but a full out 350 race engine.

Using this formula:

Carb size = CI x RPM/3456 x VE
(Engine efficiancy - VE - and a stock to a mild engine seldom exceeds 80-90%)

= 350 x 5000/3456 x .85 = 430 cfm
or another
= 350 x 6000/3456 x .90 = 546 cfm
or around town
= 350 x 3000/3456 x .80 = 379 cfm

So - you get yourself a 600 and do some tuning. I do use Edelbrocks and have used Carters - and IMHO, are the best streetable carbs. Racing - I'll go with Holleys.

And yes, you do have to tune the MSD distributors. They are set up as "optimum" out of the box, so you will have to spend some time with their owner's manual and decide how you REALLY drive the car.

Dave W
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Old 06-04-2008, 07:40 AM
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Unless the ignition equipment is faulty, it isn't your problem. It doesn't do that. A too-big, poorly tuned carb for sure causes a bog when you stab the throttle. Hopefully your 750 is a vacuum secondary model and not a double pumper. If the latter, get rid of it. You may finally get it tuned to do OK on the street but at the expense of much lower gas mileage. @ ++$4/gal, I don't think you want to go that direction? If it is a vacuum secondary model you have a fighting chance. Get a Holley secondary spring set and put in the strongest spring in the set (black). The bog should go away since the spring should lock the secondaries closed and force the carb to run as a 2-bbl. If that works, start switching in the weaker springs until the bog returns then go back to the next stronger spring. If the strongest spring doesn't cure the bog, you will need to get a smaller carb.
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Old 06-04-2008, 07:43 AM
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Is your 350 almost stock? Heads, cam, intake? That matters in picking and tuning your carb and distributor. A 600cfm carb ok on a stock 350 - 650cfm on a mild 350 - and a 350 making more than 400hp I would put a 750cfm on it if you like having more top-end power. Before you try and adjust anything else - your motor's initial and total timing must be correctly set according to your H/C/I. Then go from there onto tuning your carb.
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Old 06-04-2008, 07:47 AM
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Quote:
Originally Posted by willys36@aol.com
Unless the ignition equipment is faulty, it isn't your problem. It doesn't do that. A too-big, poorly tuned carb for sure causes a bog when you stab the throttle. Hopefully your 750 is a vacuum secondary model and not a double pumper. If the latter, get rid of it. You may finally get it tuned to do OK on the street but at the expense of much lower gas mileage. @ ++$4/gal, I don't think you want to go that direction? If it is a vacuum secondary model you have a fighting chance. Get a Holley secondary spring set and put in the strongest spring in the set (black). The bog should go away since the spring should lock the secondaries closed and force the carb to run as a 2-bbl. If that works, start switching in the weaker springs until the bog returns then go back to the next stronger spring. If the strongest spring doesn't cure the bog, you will need to get a smaller carb.
You can also tune better in those cases using carb spacers without getting another carb.
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Old 06-04-2008, 02:24 PM
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Thank you very much

this was a real help I didnt know there was such a big difference between cater and edelbrock. The engine is far from stock but by no means a race motor either. I think life will be better if I put a 600 on it then stat tuning from there, better chances any way.
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