As the others said, plug off the line at the booster, and then at the check valve to see if they are the problem first. I've had similar problems, but none were ever a blown booster. My booster is a bit newer, but even so, there are other places to check. The booster is really easy to isolate, so do that first.
Next, plug every vacuum port at the carb to see if any other vacuum line, vacuum can at the distributor, or PCV valve is the problem. Next, check the electrical to be sure you have spark at all eight cylinders. You could have burned a plug wire or had something go bad with a plug. Pull the plugs one at a time and ground them to check for spark, and of course look at them to see if they are fouled, oil soaked, gas soaked, etc. Next, check your carburetor. A stuck float or bad needle and seat could cause problems with way too much or too little fuel. Finally, once you have ruled out vacuum, fuel, and spark, you are left with the engine. Pull the valve covers and check to see if all the rockers are on the pushrods. Yes, I have seen this (in a Ford) when the nuts backed out and let one rocker fall off the pushrod. My Chevelle somehow got a bent pushrod that also made the car run really rough in a similar fashion. If lots of rockers are loose, you could have a cam that went flat on you. Not to scare you, but this is just a more complete list of things to check. Since I had the bent pushrod, I got to go through this process pretty much all the way. Of course, it also let me "upgrade" the heads as long as I was at it... Brad Waller ([EMAIL PROTECTED]) '66 Corvette | 327/dead | 4-speed | Wilwood Brakes | 245/45/16 BFG R1 '67 Chevelle | ex-SS396 | 355/700R4 | F-Body Brakes | 275/40/17 Kumho MX > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of John Nasta > Sent: Tuesday, October 11, 2005 8:48 PM > To: The Chevelle Mailing List > Subject: [Chevelle-list] suddenly running really bad > > On my way home today my engine suddenly started running > really bad. In fact, > the only way to keep it running is to leave the choke on so > that it's on > fast idle. Putting it into gear immediately sucks power away > and with my > foot on the brake on the brake it can stall, even at fast > idle. My first > guess is that it's a massive vacuum leak. Can a blown brake > booster cause > that? The booster & master cylinder are among the few things > that I haven't > changed, and I know the booster uses vacuum. > > It was getting dark as I got home so I just parked it for the > night and will > look at it tomorrow in the daylight. It was running great all > day and this > first became noticeable at a stop light about a mile from > home. I had to > keep popping it into neutral and revving the gas at lights to keep it > running. At the light before that I had done a pretty strong > takeoff to get > ahead of another guy, but I doubt that that has anything to > do with it. As I > pulled up to the curb to park, it stalled out. The brake > pedal feels really > hard like it does when the engine dies and you no longer have > the power > assist. The pedal also seems to make a different squeak then > I've ever heard > before when I step on it. So, any chance it could have to do > w/ a vacuum > leak because of a ruptured booster diaphragm? > > Any advice is appreciated. The first thing I plan to do is > check all the > vacuum lines. This is a 1969 El Camino w/ a 1958 283 w/ HEI. > > Thanks, > John Nasta > > > > >
