i have a sbc around 70-75 model with a points type distributor. I had a clutch but just went to a turbo 350 and now show a problem i did not notice with a clutch. engine dwell 28-30 timing 8 degrees with advanced unplugged 12 degrees plugged into manifold vac on edelbrock trk idles around 800-825 rpm fairly smooth. vacuum at idle around 12-13 pounds but eratic reved up to about 1200-1500 steady 18 to 20 pounds compression test great and all balanced within 1% no oil use or smoke now idling at 800-850 and drop in gear she drops idle to 425-450 and shakes like poo. it will stay running though and runs really strong. i have noticed before this new trans at idle watching timing it is eratic also holding steady at say 8 degres and then drop to 6 then bounce back to 8 with no aparant idle change. i thought timing chain sloppy, but when u grap balancer and rock back and forth with dist cap removed rotor shows no slop. thought vacuum leak but cannot find one with carb clean,wd40 or brake clean on carb or intake, unless internal intake. i had issues with no ballast resistor on truck and 12 volts to coil causing it to run like crap till i put resistor and lowered voltage. this made me screw up dwell and had points basically shut and burned them a little but i filed down. do you think points could be giving me these problem? vacuum leak internal intake? coil weak from 12volts being used on it? i want to put hei dist to elimanate ign problems but points dist is tight to fire wall now. open for any help or tips thanks howard trk runs pretty descent on rd, just vibrates so bad with low idle in gear not sure on cam, does not appear high lift. has stock sound. may check for broke valve spring maybe????
yes, temporarly tee into manifold vac with vac advance just to test trans. works fine. no taps on early manifold so will need to drill one soon. this eratic timing was with clutch also.
Worn distriutor bushings? Try checking dwell at idle and in gear, should remain constant. If the dwell changes, then the timing changes. Also only use manifold vacuum. Search for article on the HAMB written by a GM engineer who was designing ignition systems in the 60's and 70's. A very good article and he explains it well. If youu don't like the points and don't have room for an HEI then get a petronix points eliminator IF your current distributor is good.
Keep in mind that you prob never saw this with the stick, as YOU were modulating idle speed when you let the clutch out. PInch the line you ran to the vac modulator and see if the problem improves. If the modulator is blown it can cause a vacuum leak and /or suck oil into the intake. If it's originally a truck distributor, it may be getting on the advance curve by 850 so the timing would be erratic with slight fluctuations in idle speed.
Just had the same problem, leaking modulator. It wasn't sucking oil as others have in the past, so didn't think of it, until the kid brought it up. Plugged the hose, night and day difference.
The Jalopy Journal
