I would like to isolate every vacuum line from my intake and carb to confirm if I do indeed have a vacuum leak on my 69 427 AC car.
My car originally idled smooth but something has happened and now my idle is rough.

Correct me if I am wrong, but my theory is to block all vacuum lines from the carb and the intake. If this positively effects my rough idle, I can isolate where a leak may be occurring and focus on it. Most likely I have a leak in the general vacuum that does the headlights, wipe cover and anything else but I like to confirm this and see if it is actually the cause of the idle change.

I uploaded a crude diagram of my intake and carb vacuum lines for reference. I believe I have all the vacuum ports covered. 3 ports (2 on carb and 1 on intake) have been plugged from previous owner. I assume they may have to do with smog equipment and the currently non-connected AC.

So, my main question. Does this sound like a reasonable approach for general check for vacuum leaks? If I plug all currently unplugged ports and see a change in the idle, does the actually tell me I have a vacuum leak?

If I remove and plug the vacuum advance hose, will that affect my idle and should I leave it connected and plug the other 3? Im just wondering if this is a logical approach at all.

thanks
jim

 

your approach sounds good. The line going to the vacuum advance may not have a vacuum signal at idle.
Before you start anything with the hoses, does your idle improve if you partially place your hand over the primary throttle bores? If it does that shows either the carburetor mixture screws are too lean or you have a vacuum leak.

 

If it was me, I'd grab a can of carb cleaner first, and spray it around some of the vacuum fittings and the base of the carb. If it's leaking, the engine will increase RPM or smooth out in relation to the vacuum sucking in carb cleaner. For it to noticeable affect idle, I'd look at the brake booster fitting and around the base of the carb...

If that doesn't find anything, then start disconnecting/plugging vacuum lines one at a time.

 

in addition to what melwff said, I'd:
1. Brake pedal hard or do you hear a hissing noise pushing on the brake pedal? If not, that would rule out that part.
2. disconnect hose at filter and plug and see if that makes a difference.
3. spray carb cleaner at intake to head and see if idle changes

 

Thanks for all the info. I will be trying all these tests tonight.

I also was wondering if anyone knew what quadrajet I do have?

It is labeled 7208210 EE
All the pages I can find, seem to indicate a 7 digit code should start with a 70 as this 70 was the code prefix for rochester carbs.

Anyone have any ideas?

thanks

 

Sprayed carb cleaner at base of carburator today and all around the intake. I didn't notice much of a difference. I also plugged the 4 currently connected vacuum lines and it stayed the same.

While doing this I noticed a water pump leak that seems like a failure there so I am going to start a new thread for this problem.

 

be careful when spraying carb cleaner around distributer.

 

So have you checked things like plugs/plug wires, points? All of those could cause a rough idle, but if marginal, could smooth out when you give it more gas...

 

recheck the number I think you reversed something, should start with a 70 not a 72, are you looking in the correct place?
7028210 would be a 1968 Chevrolet Quadrajet manual or auto trani

http://www.carburetion.com/CarbNumbe...Number=7028210



http://www.carburetion.com/quadnumber.htm