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  #46 (permalink)  
Old 04-21-2013, 12:45 AM
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what distributor model? vacuum advance?
The distyributor cap/rotor/mag pick up phasing alignment must be within spec or the spark will scatter.
The timing retard box effects the distributor phasing..sometimes with a bad result. ( misfire, cross fire, scatter)
mag pick up wire +/- phasing. Some times it has to be reversed.

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Old 04-21-2013, 12:51 AM
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You should be able to get it to idle at 900rpm and it should not drop rpm in gear more than 100rpm.
The timing must not drop. when in gear 36deg BTDC.
let me know how it works when you get there.
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Old 04-21-2013, 05:25 AM
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Nice link for plugs......saved for future use, thanks
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  #49 (permalink)  
Old 04-21-2013, 05:27 AM
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Quote:
Originally Posted by F-BIRD'88 View Post
You should be able to get it to idle at 900rpm and it should not drop rpm in gear more than 100rpm.
The timing must not drop. when in gear 36deg BTDC.
let me know how it works when you get there.
WOW! A guy sleeps for 6 hours and wakes up to all this great info! I'll do as you say but I can't start until tomorrow. Once I get some of the meaningful information you stated I'll get back to you.
This is gonna be fun! Nothing like pros telling you how to get-r-done! Thanks for all you do!
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Old 04-21-2013, 10:51 AM
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Just so you know: with these AFB carbs it is considered normal to see a slight- short bog/throttle hesitation
when ever transitioning from a fair decent cruise speed part throttle ande then rugging the trhrottle
like say hiway crusing 60MPH and then rug the throttle Wide open. This is the nature of these air door AFB carbs.
This slight short bog is normal. An won't matter if you have 1-2 or 10 edelbrock carbs or what size .

But you will be able to tune the throttle response so it is very sharp from a dead stop, from a very low rpm
with little or no stageing preload. You want to launch right from idle or very close to that. 900 to 1500rpm.
It just takes a bit of work to get it right.
remeber reving the engine in neutral does not tell you about thottle response when driving the car.
No load winging the throttle open does not tell you anything.
What matters is the throttle response when you are DRIVING the car.
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Old 04-21-2013, 10:58 AM
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On that MSD box I would not even bother with the start retard function. I would just use a simple
spark power interupt toggle switch. This box does not actually have a dedicated cranking start retard function.
You have to use the step retard.for it. in "RPM mode" (small pink wire needs 12 volts)

A spark interupt toggle switch is easier and better. Make sure all the retard ramps and delays etc etc are disabled.
You want no retards active.

The simple interupt toggle switch goes on the small red swtiching on/off wire on MSD box.
it just turns the box on and off. You can't screw it up. You will find it second nature in a very short time.
crank it over 1-2-3 count and throw the switch to give it spark. It is just that simple.
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Old 04-21-2013, 11:06 AM
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Did you fix the carb float/flooding/ accelerator pump fuel leak problem?
get the floats set correctly.... first. I don't know why these carbs do not have a sight glass to see the fuel level
in the bowl. They are very sensitive to float setting and fuel pressure.

Remember.... the air cleaners in the blower scoop will have a effect on the carb tune.
They tend to restrict the top end horsepower, but tend to smooth out the air flow into the carbs.
They also affect the action of the secondary air doors. You will have to experiment to find what works best.

Much like the QJET carb these carbs take a bit of patience and tuning to get them right.
Once dialed in they work very well.

Last edited by F-BIRD'88; 04-21-2013 at 11:35 AM.
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Old 04-25-2013, 05:48 PM
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Quote:
Originally Posted by F-BIRD'88 View Post
You should be able to get it to idle at 900rpm and it should not drop rpm in gear more than 100rpm.
The timing must not drop. when in gear 36deg BTDC.
let me know how it works when you get there.
Well, here we go. Been working on changing the stuff you advised. Please look at the attachments when you get the time. It still bogs of-course (when I rug it) but we're getting there. Drive ability is pretty good considering.
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File Type: txt 04251300-Session 2.txt (27.7 KB, 34 views)
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  #54 (permalink)  
Old 04-25-2013, 06:07 PM
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I am going to throw this out - it worked great for me, but you need to be careful. It is all trial and hoping. I had 2 750cfm carters on a tunnel ram, on a 426 wedge. To get it to respond perfect, I took some of the weight of the air doors / butterflies. The transistion did not have any bog at any starting RPM. I launched off an idle (no trans brake) and hit N2O at the same time. It would pull the front wheels (sometimes the left rear too) and never bogged. Car ran low 10's over 138 MPH in the 1/4 on street tires. I had much better response once I took the weight off. This is not for every application - adding weight back on would be a pain, but can be done. I had other motors where I took too much off - you will know if you do - falls on its face.
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Old 04-25-2013, 09:09 PM
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Quote:
Originally Posted by 33Willys77 View Post
I am going to throw this out - it worked great for me, but you need to be careful. It is all trial and hoping. I had 2 750cfm carters on a tunnel ram, on a 426 wedge. To get it to respond perfect, I took some of the weight of the air doors / butterflies. The transistion did not have any bog at any starting RPM. I launched off an idle (no trans brake) and hit N2O at the same time. It would pull the front wheels (sometimes the left rear too) and never bogged. Car ran low 10's over 138 MPH in the 1/4 on street tires. I had much better response once I took the weight off. This is not for every application - adding weight back on would be a pain, but can be done. I had other motors where I took too much off - you will know if you do - falls on its face.
Seems like this would be a very tricky deal. Think I'll keep that as a last resort cause like you said "adding weight would be a pain". I have no way of knowing how much to remove or if it would even help in this case. I'm sure the N2O helped also.
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Old 04-27-2013, 02:52 PM
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Rich 1-3, 2-4, lean 5-7, 6-8

Pulled the new Autolite AR73 .035 gap after the 1st and last ride (about 6 miles) after installing them. 1,3 and 2,4 are showing pretty rich but 5,7 and 6,8 are showing real clean almost like new. No wonder the AFR readings in my post #53 are so screwed up. I didn't find anything wrong with either carb since checking them a week ago other than had to lower float level on the front carb just a hair to get the 7/16 drill bit under it as shown in the carb manual. Didn't find any intake leaks either.
Another question, how much will the plugs clean up after correcting the fuel problem and reinstalling them. Can I depend on the reading from them after that. Good idea to clean them with carb cleaner or ?
The plugs in the pix are lined up as they came out of the engine. 1-7 on top, right to left, 2-8 on bottom, right to left. #1 has been lightly wiped with paper towel before I thought to take the pix.
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  #57 (permalink)  
Old 04-27-2013, 08:32 PM
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The spark plugs show the front carb was clearly flooding.
Dirt in needle seat/fuel pressure/ float setting fuel filter.

Those plugs are now carbon fouled and will not clean up.
You will not be able to further tune , using these now carbon fouled plugs.
They are all now history.

Replace all the spark plugs with new. try again. You cannot tune with fouled spark plugs.

re: secondary air doors...

You are a long way away from playing with the air air door weights.
One thing at a time.
( when if you do get there you will need two spare air doors to work with as it is easier to get it wrong then right and takes work. adding/subtracting weight.. Don't jump ahead.
Get new plugs and get some more driving afr tests.

get the timing sorted out. starting with the idle timing.
Do not allow the engine to idle slow, when it is cold.
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Old 04-27-2013, 08:39 PM
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Quote:
Originally Posted by F-BIRD'88 View Post
The sparl plugs show the front carb was clearly flooding.
Dirt in needle seat/fuel pressure/ float setting fuel filter.

Those plugs are not carbon fouled and will not clean up.
You will not be able to further tune , useing these carbon fouled plugs.

Replace all the spark plugs with new. try again.

You are a long way away from playing with the air air door weights.
One thing at a time.
( when if you do get there you will need two spare air doors to work with as it is eaier to get it wrong then right and takes work. adding/subtracting weight.. Don't jump ahead.
Get new plugs and get some more driving afr tests.
Plugs are getting expensive. lol Rather not mess with air door weights if I can help it. Will get back to u after I get things straightened out.
Thanks for all your help.
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Old 04-28-2013, 10:38 AM
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You got one too many 750's



Duke
I agree totaly.1500 CFM is too much for a 355 even with all the goodies.
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Old 04-28-2013, 10:42 AM
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It's all in the tune. I'm competent a good tuner well have something worthwhile to say.
Even a good tuner will tell you that you need to have the right fuel/air ratio.You have too much air and if you jet it down enough to get the bog out it will be too lean for top end and probably melt a piston.
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