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vacuum advance trouble

3K views 9 replies 7 participants last post by  454C10 
#1 ·
purchased an 86 chevy w/ a 305. has an edelbrock performer intake and 600cfm carb. has an msd ignition box and dist.cap and rotor. changed carb to a quad jet and have timing as close as possible by ear and eng performance. unable to find a timing marker ANYWHERE. removed most vacuum lines needed for emissions. have big line from carb leading to pcv on valve cover. other carb vac line plugged. need ideas for installing my vacuum advance to a vac line that will increase vac w/ increase in acelleration. tried to use small line on carb but it put dist. in advance all the time. thinking of drilling a hole in bottom of aircleaner and running vac advance to it.... any thoughts, suggestions and help is appreciated.
 
#2 ·
vacumn advance

Hi my name is Nial the air cleaner wont supply any vacumn at all. You have two types of vacumn you can use . manifold vacumn, it will decrease the harder you step on the throttle and be highest when off the throttle. This is best for gas mileage.
Port vacumn, It will increase when you got on the throttle.
Manifold vacumn you feel with your finger on the end of the hose. Port vacumn is hard to feel. You will feel it as the engine is accelerating.
Have a good day Nial
 
#3 ·
vac adv.

the only vacuum i have is on the carb and i ran that to the pcv. there is another vac port on carb but when i use that for vac adv it runs high all the time. so i need a port that has minimal vac while idle and increases w/ acceleration. have a few vac ports on manifold but they have no vac at all. ever. they are not working. unless it is such a small amount i cant feel it, but seems unlikely. will try it anyway.

thanx
 
#4 ·
305rocker said:
the only vacuum i have is on the carb and i ran that to the pcv. there is another vac port on carb but when i use that for vac adv it runs high all the time. so i need a port that has minimal vac while idle and increases w/ acceleration. have a few vac ports on manifold but they have no vac at all. ever. they are not working. unless it is such a small amount i cant feel it, but seems unlikely. will try it anyway.

thanx
Use the manifold vacuum port, and re-adjust your base idle speed to your final speed you are comfortable with.

Your base timing is set with it disconnected, and plugged. This may be somewheres between 0, and 12 degrees initial timing.

The amount of advance with it hooked up, will make a huge difference in fuel mileage saving, and performance.

This in turn can cause engine failure, if any detonation/pinging is heard.

PM me with any question's.

Stephen
 
#5 ·
rocker u would be best advised to first find tdc and verify your timing marker with the dampener circumference. search wiki for finding TDC and Making a timing tape, do this and get a timing light and a vacuum gage, then tuning the thing will give results.

The only piece hooked up to the air cleaner should be the air breather on the valve cover opposite the PCV valve, dist vacuum is not sourced at the air cleaner.
 
#6 ·
nialkc said:
Hi my name is Nial the air cleaner wont supply any vacumn at all. You have two types of vacumn you can use . manifold vacumn, it will decrease the harder you step on the throttle and be highest when off the throttle. This is best for gas mileage.
Port vacumn, It will increase when you got on the throttle.
Manifold vacumn you feel with your finger on the end of the hose. Port vacumn is hard to feel. You will feel it as the engine is accelerating.
Have a good day Nial
The ported vacuum will also drop off when you step on the throttle harder.
 
#7 ·
If you are running a quadrajet there is almost always a small vacuum port above the baseplate on front right side of carb for distributor advance. As advised you gotta start with getting it timed properly. You are probably way off if you are timing by ear, Thats like building a house without a level. No vacuum at intake manifold port... WTF?? That sounds impossible to me. I bet your timing is way advanced.
 
#8 ·
not sure if timing is exact, but it runs pretty damn well now. i found tdc and installed dist. had to adv it completely to run. removed dist and found tdc again. turnd the screw under dist 180* and now its close. has good idle, accel and power. put when peddle is fully pressed it stalls. the edelbrock intake manifold has a plugged hole behind carb. and a vac port on top of AND next to therm housing. no vac there. either place. i imagine if ALL vac lines where connected they would work, but most were cut and removed before i bought the truck. wonder if the plugged port would work.... the small vac line on right side of carb put the idle very high ALL the time. does that mean i am advanced too much and it has too much vac?
 
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