Vacuum advance issue on roller motor

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Mr. Plater

Mr. Plater

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Hey guys im at a loss here i figured its time to post. i have a 440 4barrel in a 68 cuda. the motor was professionally built. it is bored 30 over, taller pistons, 10:1 compression, roller rockers, roller lifters, hydralic roller comp cam .540 lift from 440 source, 3000 stall converter, using 91 octane. my machinist lost my cam card so i dont know all the specs on it and am not able to find the exact specs on the website. i have my initial timing set at 24btdc with no vac adv hooked up, the car idles great with this setting. then i go to hook up my vaccum advance, and the timing values are all over the place, sometimes it sits at 55 total advance at 2800 which is per mopar specs, and sometimes the timing retards by itself and motor dies as it is idling. i know the timing is slowing down becuase i used the timing light and watched it happen on the balancer. Im about to unhook the vacuum advance all together. when the car is running and the vaccum advance is hooked up, the timing slowly retards itself until the car dies and smoke comes out of the exhaust ports. it does this about half of the time, the other half it runs as it is supposed to. I have the distributer marked in relation to the block and tight so i know that the distrubuter snt moving on its own. When Vac Adv isnt hooked up it idles great and doesnt die on its own like when the vac adv is hooked up. any suggestions?
 
Mr. Plater said:
timing values are all over the place, sometimes it sits at 55 total advance at 2800 which is per mopar specs, and sometimes the timing retards by itself and motor dies as it is idling.
Click to expand...

You need to get to the bottom of this before even worrying about transfer slot position... check to make sure you have the pickup polarity wired correctly first (ask how I know). Then check reluctor gap and rotor phasing.
 
ok guys, I re did my timing once again and she seems to be running well and behaving today and staying in time finally. Perhaps it was something I was doing wrong previously. Vcan is hooked up to the ported vacuum port. ill see how she runs tomorrow. im hoping that it was some kind of fluke.
 
If you need 24 degrees initial it tells me something is wrong elsewhere.
What is the rest of the timing curve like?
What distributor?
What rpm is it idling at?
Is there vacuum present at the ported vacuum nipple at idle?
Are you sure the vacuum dashpot on the distributor is good?
What vacuum level is it pulling at idle? At light throttle cruise?
 
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