Koz

I still have a miss/hessitation/rough idle/ won't hold a steady RPM problem. I replaced the cap, rotor, plugs, fuel filter and now rebuilt carb and I still have the same problem. I put a timing light on all the wires and they all fire.. They mechanic that did the carb said it sounds like a vacuum leak. He suggested I use a pair of plyers and do the pinch test on all the vacuum lines. "There's a lot of vacuum hoses running through these cars" he said.. Well that's a PIA.. Since the miss is noticable at idle and slight acceleration (1500 rpm) would plugging all the vacuum ports on the carb and intake determine if it is vacuum or something else? I tried this on the head light vacuum cause I know I have a problem holding vacuum to close the doors after engine shuts off so I just unpluged the hose by the filter next to the manifold and put my finger over the hose.. Problem still there so no matter what's wrong up front with the reserve tank, that's not causing the rough ride.. Can I do that will all the ports on the carb except the one for the distributor advance to isolate which "line" has the "possible" leak? Would this work or not and why? Any other lines a must have to run smooth at idle?

john's '81 mouse

Start at the carb. and intake and work your way out, away from the engine to find vacuum leak. Make sure you don't have a leak where intake meets the heads, and carb. meets the intake (fairly common, frequent problem). Get a spray can of carb. cleaner and spray by these areas when engine is at idle, and if idle speeds up, smooths out when spraying, then you've found at least one of your leaks.

Also have heard of smokers blowing smoke into vacuum hoses and then looking for where smoke escapes to find leaks in hoses and vacuum related devices on vettes. Use of a hand held vacuum pump also is good way to find leaks.

Good luck!

Sigforty

I traced down my vacuum leaks with a cigar. I first eliminated the reserve tank by using a T to connect the three lines plugged into it. After I knew The tank was not a problem I started blowing smoke throught the lines at the tank. Then I looked for the smoke exiting the car. My problem turned out to be a wiper relay valve in my fender. I may help to have an extra person to look for the smoke. I almost missed it looking at other locations.

Mark B.

Koz

I'll buy a cigar on the way home if it will help me... :) But will pulling hoses off the carb and intake and pluging the carb give me an idea of which line to smoke test or if it's in the lines at all or maybe the intake? I have a can of carb cleaner so maybe I'll spray the bottom of the carb and intake seams first since that may be the easyest test to do.. Any other ideas that could cause my symptoms.?

bigbobbyb

Another trick I learned from a friend who races is to use a propane torch....NOT LIT....and basically just open it up a bit and point at the various vacuum lines/connectors while the car is running. When you hear the engine rev from the propane, you've found a leak. This should be done outdoors!!



[Modified by bigbobbyb, 12:29 PM 5/22/2002]

dlw

In my case, my vacuum leak turned out to be numerous leaks instead of just one. I ended up replacing all the relays and a couple of hoses. I used my air compressor to blow air into the system and just listened for the leak in a very quiet garage. Once I got close to the sound, I felt around the hose/relay with a wet hand untill I could feel the air. Worked for me.

andyg

I am currently working this issue. I plugged the port at the intake and my idle went from shaky to smooth, so I know it was a vacuum leak. I purchased a vacuum pump with a guage to start testing. I found both relays were leaking bad. I am also going to replace as many hoses as possible with a new hose kit. A PITA, but it must be done.

---Andy


[Modified by andyg, 8:53 PM 5/22/2002]

joeveto

The job sounds like a major PIA, but it's really not that bad. I rented a vacuum pump from AutoZone, cracked open a beer, and two hours (and a beer or two later) I knew exactly where my problems were. I'd disconnect each hose, hook up the pump, plug the other side, listen and watch. If the hose was good, I'd move on. If not...

I also tested each relay/switch whatever. My problem was a bad carb to air cleaner gasket and a bad headlight actuator. Now my engine is smooth and my headlights work.

Truly, it only takes an hour or two, and you'll learn a lot.

Koz

It feels so good when you get an idea and it works. I purchased some hose and made stubs about 3inch long with a bolt in the end. I capped all hoses off the carb and the intake to master brake. Started her up and she held a steady idle.. One by one I replaced hoses and when I replaced the line that fed the EGR she wouldn't hold steady. I recaped that line and continued the testing. All the other lines tested fine so I went back, reconnected the EGR line but plugged it at the EGR. Again she ran steady.. unplugged and hooked up the EGR and she wouldn't hold steady.. I found my problem!! Thanks to all that helped.. :cheers: