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  #16  
Old Dec 25th, 12, 04:42 PM
Gar's67 Gar's67 is offline
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Gary
 
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Default Re: Jets and Carbs

I agree with the "Pump Cam" comments. Use this chart as a reference. Just for kicks, I'd throw a Blue pump-cam on her:
http://www.quickfueltechnology.com/I...-41141-100.pdf
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  #17  
Old Dec 25th, 12, 04:50 PM
alanrw alanrw is offline
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Default Re: Jets and Carbs

I'm with Mike on this one. A vacuum advance would help considerably. It is fairly easy to try larger squirters or different acc. cam profiles, Holley has a chart which shows pump volume based on cam plastic color. Just make sure the butterflys are closed and use a rag when swapping out acc. pump jets. It is really a pain when the screw or jet falls into the intake manifold.

alan
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  #18  
Old Dec 25th, 12, 07:52 PM
Melrose RS Melrose RS is offline
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Carb came with a 4.5 power valve and you are running a 3.5 if i understand correctly. And when you are rolling along, low speed, high vac situation and ease into it, as vac drops below your 7", it stumbles. Sounds like it is going lean when the power valve should be coming in. I would go back to the 4.5 and try that. That pv will come in sooner.
I went thru a similar problem tuning a Holley 4360 but i had my A/F meter which was a big help. Tuning the power valve got it smoothed out.


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  #19  
Old Dec 26th, 12, 09:10 AM
MW67RS MW67RS is offline
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Matt
 
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Default Re: Jets and Carbs

If it stumbles at slight throttle openings but is fine when the throttle is opened more it sounds to me like the throttle pump arm isn't in contact with the cam. This results in slight rotation of the cam without movement on the accelerator pump.

What cam and discharge nozzle are you using?
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  #20  
Old Dec 26th, 12, 12:05 PM
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RJBaileyrn RJBaileyrn is offline
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Default Re: Jets and Carbs

No slop in accelerator pump linkage.
As for the mechanical advance distributor, if I had it to do over again, I would get a dizzy with vacuum canister, but I'm probably not going to pull the MSD distributor and spring for big bucks on another one.
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  #21  
Old Dec 27th, 12, 09:27 PM
Truckarm Truckarm is offline

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Default Re: Jets and Carbs

Just a thought with more info. How much vacuum at idle and just off idle? Two words though, Vacuum canister !
This may be applicable to your situation. Just my 2 cents. Its worth a look. This is from a magazine article. Not saying to drill your throttle blades, but you may want to look at your idle transfer slots. How much throttle opening is your carb set to get it to idle ?
Hope this helps.

Setting Idle Speed
The problem with a long-duration camshaft with lots of overlap is low manifold vacuum that requires more throttle opening to set the proper idle speed. The ideal position of the throttle blades in relation to the idle transfer slot is where the primary throttle blades just barely uncover the bottom of the transfer slot-roughly about 0.020 inch. However, long-duration camshafts often demand much more throttle opening. This uncovers too much of the idle transfer slot delivering more fuel from the idle circuit. This creates an off-idle hesitation or bog that is difficult to eliminate. If the curb idle speed position of the primary throttle blades uncover to much of the idle transfer slot, the quick fix is to drill two small holes in the primary throttle blades adjacent to the transfer slot. Start with holes of roughly 1/32 inch in diameter and then readjust the idle speed on the carb. Adjust the hole size, idle speed, and throttle-blade position until you achieve a blade that uncovers no more than .020 of the idle transfer slot.
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  #22  
Old Dec 28th, 12, 07:19 PM
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RJBaileyrn RJBaileyrn is offline
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RJ
 
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Default Re: Jets and Carbs

Thanks for the good ideas and info.
I went back to 4.5 power valve in front and removed the plug in the secondaries and put in 4.5 power valve there too, and upped my primary jets to #74s, and decreased the rears from #84s to #74s.
idol vacuum is 9", and the car now eases of of idol with no hesitation at all, much better than what it was. I still have "roughness" from 1500-on up to 2500 or so, maybe a touch more, and then it runs very smooth from then on up to 6500. The roughness i speak of is similar to the rough cam idol, but I would have thought that would disappear by 1500rpm max, but maybe I'm wrong, I never had this aggressive of a camshaft before, soo wasn't sure what to expect.
Also had a fouled #4 plug. replaced it, checked the resistance on the MSD wires which was good, and then checked the MSD distributor cap and found that the terminals in the cap were quite corroded. I cleaned them with some sandpaper, pup it back together with a new spark plug, and the misfire was gone. That of course helped alot with the idol.
Not sure if the roughness up to 2500 is normal, or if there is further adjustment necessary. I dont have the extra case to spring for a vacuum distributor right now, or I would make the change.
Thanks all.
RJ
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  #23  
Old Dec 29th, 12, 04:55 AM
r_w r_w is offline
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If you are gently rolling up to cruise and getting roughness below 2000 rpm you are running mostly on the t slots and idle circuits. Probably a touch lean. If you have already properly adjusted idle you would have to tweak your IFR's or IAB's to change that. Without an AFR curve I'd just be guessing, I'm not as good as the old school guys...


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  #24  
Old Dec 29th, 12, 06:54 AM
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RJBaileyrn RJBaileyrn is offline
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RJ
 
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Default Re: Jets and Carbs

I was thinking about going up to #76s on the primary and giving that a try. Before, I was having issues with the plugs fouling. That's when I replaced the rear plug with a 4.5 power valve and reduced the rear jet size from #84 to #74. Really cleaned up the plugs after that.
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