vacuum issues with my 68
Thread Starter
Racer
Joined: May 2009
Posts: 316
Likes: 1
vacuum issues with my 68
My 68 327 is pulling 10 on my vacuum gauge. I have done all the checks I can think of to locate any possible leaks including propane and carb cleaner as will as smoke. Still cant find the problem. vacuum gauge suggests late valve timing or leak at intake manifold. What is late valve timing and how does it occur? It has also been suggested to me to replace the carburetor as a solution. Would a carb problem cause a vacuum issue (there are no leaks at the base to manifold that I can find)?
Safety Car
Joined: Sep 2011
Posts: 4,115
Likes: 1,230
From: Madeira Beach, FL
2024 C8 of the Year Finalist - Unmodified
2024 C2 of the Year Finalist - Unmodified
2023 C2 of the Year Finalist - Unmodified
2020 C3 of the Year Finalist - Unmodified
Greg,
carb has its own set of problems and leaks internally.
I recently replaced a crappy commercial rebuilt quadrajet with a new in the box old stock Edelbrock 1401.
My vac went from a fluttering 15-16lbs to 21 lbs.
Before you go crazy and start taking things off, swap out the carb first.
Maybe possible to find a used Edelbrock or Holley just for gauging the problem. If it an orig. carb to car send it out to Lars. He's on this site frequently and his email is all over the forum just search for Lars.
You could also do a leak down test to find out why your vac is low?
Hope this helped. There will be more knowledgeable answers than mine to come. This forum has a wealth of experienced members.
Marshal
carb has its own set of problems and leaks internally.
I recently replaced a crappy commercial rebuilt quadrajet with a new in the box old stock Edelbrock 1401.
My vac went from a fluttering 15-16lbs to 21 lbs.
Before you go crazy and start taking things off, swap out the carb first.
Maybe possible to find a used Edelbrock or Holley just for gauging the problem. If it an orig. carb to car send it out to Lars. He's on this site frequently and his email is all over the forum just search for Lars.
You could also do a leak down test to find out why your vac is low?
Hope this helped. There will be more knowledgeable answers than mine to come. This forum has a wealth of experienced members.
Marshal
Instructor
Joined: Nov 2013
Posts: 131
Likes: 5
When you say 10 psi at what rpm is this at idle. My 427 at 800rpm is around 7-8 pounds of vac and will go to 0 vac after quick wide open throttle for a mil second then goes to 25 pounds vac running around 2000 rpm. My motor does have a few mods like cam and just rebuild from top to bottom. I am not sure what is normal vac which would be nice to know.
Melting Slicks
Joined: May 2012
Posts: 2,192
Likes: 343
From: Allenton Wisconsin
Are you checking the engine vacuum with the accessory vacuum circuit disconnected and plugged. Also you cannot really trust the timing marks on an original balancer to be accurate. The balancers do slip over the years. Try moving the dist and see what that does for your vacuum. Your 327 will run good with 32 to 36 degrees of total timing. T
Thread Starter
Racer
Joined: May 2009
Posts: 316
Likes: 1
When you say 10 psi at what rpm is this at idle. My 427 at 800rpm is around 7-8 pounds of vac and will go to 0 vac after quick wide open throttle for a mil second then goes to 25 pounds vac running around 2000 rpm. My motor does have a few mods like cam and just rebuild from top to bottom. I am not sure what is normal vac which would be nice to know.
Thread Starter
Racer
Joined: May 2009
Posts: 316
Likes: 1
Are you checking the engine vacuum with the accessory vacuum circuit disconnected and plugged. Also you cannot really trust the timing marks on an original balancer to be accurate. The balancers do slip over the years. Try moving the dist and see what that does for your vacuum. Your 327 will run good with 32 to 36 degrees of total timing. T
