Vacuum/High idle issues
Thread Starter
Intermediate
Joined: Mar 2022
Posts: 33
Likes: 1
High idle/Vacuum issues
Got a 72 c3 couple days ago. Blueprint crate 350 was put in a few years ago. Holley 600 carb. auto car. Here’s the issues I’m facing thus far any help is appreciated!
Vacuum- headlights don’t come up nor does the wiper door open (not sure of a leak or what yet, have yet to check)
High idle- car started idling high (intermittently) literally when the guy pulled up the other day (he says it did it for the first time when he pulled up then) when you throw it in park it’ll jump to crazy high rpm like 1800-2k. In Drive it’ll idle at 1k. Messed with the idle screw and such and nothing. I’ll be sitting at a stoplight while idling at around 1k and it’s hard to hold the car back.
I’m thinking all of these issues (wiper door, headlights not coming up and high idle) are coming from vacuum.
It also has a slight oil leak around the front and back of the intake due to a messy looking gasket job. I’m really hoping not to pull the intake right now as it’s unfortunately my daily driver until February. Runs great, 150 mile nonstop trip back home when I got it.
Other issue not drive wise is the dreaded water leak I found out just now before I came to work, water in floorboards and was dripping from the front of the T tops.
Any help is appreciated!
Vacuum- headlights don’t come up nor does the wiper door open (not sure of a leak or what yet, have yet to check)
High idle- car started idling high (intermittently) literally when the guy pulled up the other day (he says it did it for the first time when he pulled up then) when you throw it in park it’ll jump to crazy high rpm like 1800-2k. In Drive it’ll idle at 1k. Messed with the idle screw and such and nothing. I’ll be sitting at a stoplight while idling at around 1k and it’s hard to hold the car back.
I’m thinking all of these issues (wiper door, headlights not coming up and high idle) are coming from vacuum.
It also has a slight oil leak around the front and back of the intake due to a messy looking gasket job. I’m really hoping not to pull the intake right now as it’s unfortunately my daily driver until February. Runs great, 150 mile nonstop trip back home when I got it.
Other issue not drive wise is the dreaded water leak I found out just now before I came to work, water in floorboards and was dripping from the front of the T tops.
Any help is appreciated!
Thread Starter
Intermediate
Joined: Mar 2022
Posts: 33
Likes: 1
Vacuum/High idle issues
Got a 72 c3 couple days ago. Blueprint crate 350 was put in a few years ago. Holley 600 carb. auto car. Here’s the issues I’m facing thus far any help is appreciated!
Vacuum- headlights don’t come up nor does the wiper door open (not sure of a leak or what yet, have yet to check)
High idle- car started idling high (intermittently) literally when the guy pulled up the other day (he says it did it for the first time when he pulled up then) when you throw it in park it’ll jump to crazy high rpm like 1800-2k. In Drive it’ll idle at 1k. Messed with the idle screw and such and nothing. I’ll be sitting at a stoplight while idling at around 1k and it’s hard to hold the car back.
I’m thinking all of these issues (wiper door, headlights not coming up and high idle) are coming from vacuum.
It also has a slight oil leak around the front and back of the intake due to a messy looking gasket job. I’m really hoping not to pull the intake right now as it’s unfortunately my daily driver until February. Runs great, 150 mile nonstop trip back home when I got it.
Other issue not drive wise is the dreaded water leak I found out just now before I came to work, water in floorboards and was dripping from the front of the T tops.
Any help is appreciated!
Vacuum- headlights don’t come up nor does the wiper door open (not sure of a leak or what yet, have yet to check)
High idle- car started idling high (intermittently) literally when the guy pulled up the other day (he says it did it for the first time when he pulled up then) when you throw it in park it’ll jump to crazy high rpm like 1800-2k. In Drive it’ll idle at 1k. Messed with the idle screw and such and nothing. I’ll be sitting at a stoplight while idling at around 1k and it’s hard to hold the car back.
I’m thinking all of these issues (wiper door, headlights not coming up and high idle) are coming from vacuum.
It also has a slight oil leak around the front and back of the intake due to a messy looking gasket job. I’m really hoping not to pull the intake right now as it’s unfortunately my daily driver until February. Runs great, 150 mile nonstop trip back home when I got it.
Other issue not drive wise is the dreaded water leak I found out just now before I came to work, water in floorboards and was dripping from the front of the T tops.
Any help is appreciated!
Pro
Joined: Feb 2002
Posts: 734
Likes: 51
From: ATLANTIC HIGHLANDS NJ
Yes, many vacuum lines. Easiest method is to first plug all vacuum lines except vacuum advance. Start car, warm it up, choke off. Pull and plug vacuum advance, rpm should drop, indicating vacuum advance is functioning. Now with low idle spray brake clean, or similar, around base of carb, carb throttle shaft, intake sides/ends. An increase in rpm will locate vacuum leak if it's engine related. If not now hook up other vacuum lines one at a time to find source of any vacuum leaks.
I can tell you on my 73 my high idle was the PCV link down to the charcoal cannister.
I summary these C3's vacuum systems seem complicated but can be simple to fine tune thru a step by step approach IMO.
Doug
I can tell you on my 73 my high idle was the PCV link down to the charcoal cannister.
I summary these C3's vacuum systems seem complicated but can be simple to fine tune thru a step by step approach IMO.
Doug
Race Director
Joined: May 2006
Posts: 18,734
Likes: 2,582
check for a vacuum hose that has come disconnected from the intake manifold or carburetor that would cause a massive vacuum loss. Also check the vacuum reservoir located I believe on the drivers side inner fender.
Drifting
Joined: Oct 2020
Posts: 1,567
Likes: 576
From: Wisconsin
Your mention of the messy intake gasketing is a potential clue: you may have a vacuum leak at an intake port on the manifold.
If you exhaust all other vacuum leak sources and still have the issue, its time to pull the intake.
If you exhaust all other vacuum leak sources and still have the issue, its time to pull the intake.
Advanced
Joined: Aug 2022
Posts: 91
Likes: 34
From: North Lincolnshire, England
I had a similar problem. One of the things I had to sort out was the choke was still on slightly when the engine was warmed up, this could mean that the high idle is still activated.
Make sure that once the engine is warm the choke plates are in the fully vertical position and not at a slight angle off vertical.
Once I got that sorted, it was simply a matter of turning down the regular idle on the drivers side of the car and it was just about ready to go.
Make sure that once the engine is warm the choke plates are in the fully vertical position and not at a slight angle off vertical.
Once I got that sorted, it was simply a matter of turning down the regular idle on the drivers side of the car and it was just about ready to go.
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Race Director
Joined: May 2006
Posts: 18,734
Likes: 2,582
watch your tachometer at idle. Disconnect a small active vacuum line behind the carburetor and watch the tach. It's the same as cracking the throttle a little, you let more air in but it goes lean since no additional fuel.
Pro
Joined: Apr 2010
Posts: 603
Likes: 249
From: Carson Valley
The OP's car may have been running ragged and rough, due to a lean condition caused by a vacuum leak, and someone adjusted the idle mixture screws to richen it up.
Introduce enough air through a vacuum leak and the carb idle screw won't be able to compensate.
Le Mans Master
Joined: Jun 2019
Posts: 7,656
Likes: 2,469
From: Indiana
OP..
i would suggest a few things.. first congrats on your car !!
- are the bolts securing the carb snug? not over tight but snug? like hard hand screwdriver tight?
- keep out of rain or cover best you can realizing daily driver.. pretty sure they all will leak eventually..
- if headlights do not work at all it probably is not a leak unless massive.. do you have diagrams? AIM or service manual?
- let's see your ride!!! take lots of pics of the issues you want to resolve as well like angles of carb engine etc..
there are great people on hear eager to help..
good luck!
i would suggest a few things.. first congrats on your car !!
- are the bolts securing the carb snug? not over tight but snug? like hard hand screwdriver tight?
- keep out of rain or cover best you can realizing daily driver.. pretty sure they all will leak eventually..
- if headlights do not work at all it probably is not a leak unless massive.. do you have diagrams? AIM or service manual?
- let's see your ride!!! take lots of pics of the issues you want to resolve as well like angles of carb engine etc..
there are great people on hear eager to help..
good luck!