vacuum advance
#1
12-19-2007, 01:12 PM
Join Date: Apr 2007
Location: Virginia Beach Virginia
Posts: 176
vacuum advance
When I step on the gas pretty hard, my engine pings pretty bad. If I just ease on my gas it speeds up just fine. A friend at work suggested I check my vacuum advance coming off my distributor, he said that it may not be working. I looked at my distirbutor and the "diaphram" (not sure what you call it, where the vacuum hose connects) looks pretty rusty. Also, the vacuum hose runs from the distributor to the passenger side of the carburator (holly 650). Is this correct? If not, where should it connect to? To replace the vacuum advance thing on the side, do I just pop the distributor off and bolt the new one on? I don't want to get into something that is above my head. Thanks.
#2
12-19-2007, 02:31 PM
RE: vacuum advance
Hi again and Happy Holidays.
If the engine pings when you step on it you might have to much timing.
Warm the motor up and disconnect the vacuum line where it connects to the vacuum can and plug the line.
Now loosen the distributor hold down bolt and set the timing to whatever the book calls for, lets say 8*.
Then reconnect the vacuum line and check the timing again, if the can is working you should read about 16* more.
Initial timing= 8*
Vacuum advance adds 16*
Total= 24*
The vacuum advance line should be connected to " Full Manifold Vacuum", if you have a vacuum guage you can connect it where you disconnected the hose at the vacuum can.
When you step on the gas you loose Manifold vacuum untill you get to a steady speed and for these few seconds the vacuum can does not add any timing.
The next thing that happens is as the engine speeds up the Centrifugal advance weights inside the distributor spin out and they ad more timing.
If the vacuum can is no good you will have to pull out the distributor to change it. PG.
If the engine pings when you step on it you might have to much timing.
Warm the motor up and disconnect the vacuum line where it connects to the vacuum can and plug the line.
Now loosen the distributor hold down bolt and set the timing to whatever the book calls for, lets say 8*.
Then reconnect the vacuum line and check the timing again, if the can is working you should read about 16* more.
Initial timing= 8*
Vacuum advance adds 16*
Total= 24*
The vacuum advance line should be connected to " Full Manifold Vacuum", if you have a vacuum guage you can connect it where you disconnected the hose at the vacuum can.
When you step on the gas you loose Manifold vacuum untill you get to a steady speed and for these few seconds the vacuum can does not add any timing.
The next thing that happens is as the engine speeds up the Centrifugal advance weights inside the distributor spin out and they ad more timing.
If the vacuum can is no good you will have to pull out the distributor to change it. PG.
#3
12-19-2007, 02:46 PM
RE: vacuum advance
another way to test ;engine running,remove vac hose from dist and feel for vac. at hose if none raise idle to 1200 and recheck for vac. if ya got vac raise dist. 'door' while looking inside connect vac hose. you will see the plate move if advance is good.check basic timing first.YOU DO NOT HAVE TO REMOVE DIST TO R+R ADVANCE.ill tell ya an easier way but i doubt this is the trouble unless its is bad and someone jacked the timing up to compensate.this just start doing this
#4
12-19-2007, 04:02 PM
Join Date: Apr 2007
Location: Virginia Beach Virginia
Posts: 176
RE: vacuum advance
I checked for vacuum and did not have any. I am changeing out the vacuum can and I will let you know the results. Thanks for the help.
#5
12-19-2007, 06:08 PM
RE: vacuum advance
Whoa, no vacuum? 
Did you check the hose "from" the carb, or did you check "from" the can? No vacuum does not mean the can is bad.
Disconnect the hose from the can to find out if you have vacuum from the carb.If no vacuum, you have a plugged line or the line is not connected to the right place on the carb.
You can watch the vacuum advance linkage at the dist. If it moves while running engine at different speeds,the can isO.K.
Did you check the hose "from" the carb, or did you check "from" the can? No vacuum does not mean the can is bad.
Disconnect the hose from the can to find out if you have vacuum from the carb.If no vacuum, you have a plugged line or the line is not connected to the right place on the carb.
You can watch the vacuum advance linkage at the dist. If it moves while running engine at different speeds,the can isO.K.
#6
12-20-2007, 05:10 AM
Join Date: Apr 2007
Location: Virginia Beach Virginia
Posts: 176
RE: vacuum advance
I guess I mis understood the whole thing. The can was ok. The guy at advance told me to install a valve into the vacuum line (to hold the vacuum I guess) and it helped a little. I think the timing must be out of wac. Don't have the tools (timing light) to do this so I guess I have to take it to the shop.
Thanks
Thanks
#7
12-20-2007, 07:33 AM
RE: vacuum advance
Ya might think about getting a timing light. They are cheeper than takin' it to a shop, and with a little practice, you can do just as good a job of setting the timing. There is an amount of satisfaction in doing your own work, and ya save a few bucks too. 
I've developed and "ear" for tuning my engines. With the engine running I can set timing, adjust points, and tune in the carb. (and never use a light) All it takes is practice.
I've developed and "ear" for tuning my engines. With the engine running I can set timing, adjust points, and tune in the carb. (and never use a light) All it takes is practice.
#9
12-20-2007, 02:29 PM
Join Date: Apr 2007
Location: Virginia Beach Virginia
Posts: 176
RE: vacuum advance
The Corvette sat for about 2 years before I bought it in July of this year for 7800. The interior is all new and the outside is in real good shape with a few cracks in the paint. I had to put a new carb on it when I bought it (the old one was beyond repair) and replaced the transmisson pan gasket because of a leak. The engine has always started pinging when I step on the gas real hard. I know I have a transmission problem, it does not down shift when I get on it either. That was my next project. Well I was out driving it last night to see if the valve on my vacuum hose helped (it did a little) and started smelling burnt tranny fluid. Brought it home, jacked it up and it looks like the front seal on the tranny is in need of replacement. It is leaking real bad up at the front of the transmission. I guess that will be my christmas present (that is definetly out of my league). I will go out and get a timing light since I plan on keeping the vette. Know of a dependable transmission guy in Virginia Beach Virginia?
Dan
Dan
#10
12-20-2007, 09:48 PM
RE: vacuum advance
ORIGINAL: riley6riley
The Corvette sat for about 2 years before I bought it in July of this year for 7800. The interior is all new and the outside is in real good shape with a few cracks in the paint. I had to put a new carb on it when I bought it (the old one was beyond repair) and replaced the transmisson pan gasket because of a leak. The engine has always started pinging when I step on the gas real hard. I know I have a transmission problem, it does not down shift when I get on it either. That was my next project. Well I was out driving it last night to see if the valve on my vacuum hose helped (it did a little) and started smelling burnt tranny fluid. Brought it home, jacked it up and it looks like the front seal on the tranny is in need of replacement. It is leaking real bad up at the front of the transmission. I guess that will be my christmas present (that is definetly out of my league). I will go out and get a timing light since I plan on keeping the vette. Know of a dependable transmission guy in Virginia Beach Virginia?
Dan
The Corvette sat for about 2 years before I bought it in July of this year for 7800. The interior is all new and the outside is in real good shape with a few cracks in the paint. I had to put a new carb on it when I bought it (the old one was beyond repair) and replaced the transmisson pan gasket because of a leak. The engine has always started pinging when I step on the gas real hard. I know I have a transmission problem, it does not down shift when I get on it either. That was my next project. Well I was out driving it last night to see if the valve on my vacuum hose helped (it did a little) and started smelling burnt tranny fluid. Brought it home, jacked it up and it looks like the front seal on the tranny is in need of replacement. It is leaking real bad up at the front of the transmission. I guess that will be my christmas present (that is definetly out of my league). I will go out and get a timing light since I plan on keeping the vette. Know of a dependable transmission guy in Virginia Beach Virginia?
Dan
Timing light -costs about $60. Get a Dial back, its got a **** on the back and it makes timing a piece of cake.
Vacuum guage-very usefull, theres lots to check on a Vette.
Everyone on this forum will help you every step of the way, so if you need help just ask.
When I first got my Vette every time I wen't for a ride something else broke or needed some work.
I took a ride one day and nothing broke, then I put my turn signal on to turn into my blockand it broke.
Happy Holiday! PG.