I have a 64 riviera with a 425-4 barrel. I can't seem to get the idle to smooth out. I put in a new carb kit, plugs, points and fuel filter. The timing is set @ 2.5 and the dwell at 30. I hooked up a vacuum gage and get a reading between 18 and 21'" with a very fast fluctuation. I have plugged all vacuum lines except the brake and transmission. I sprayed carb cleaner around the intake manifold and carb base with no noticable change in idle. I'm running out of things to try and am thinking it might be a valve problem. I am also pinging at high rpms. Anybody have any ideas?
try this First run a compression test, that will tell you if the engine can be made to run or if you have to correct some mechanical problem. then if that test is good. [90 psi or better on all cyls] ck the vacume diaphragm on the dist. to see if it will hold a vacume. Vac flux suggests that a valve may not be sealing for what ever reason, unless it has a hotter cam. A hotter cam will cause flux at idle.
valve problem I have checked the vacuum at the dist. and it holds. I did a comp. test with the following results: cyl. #1-152psi #2-174psi #3-160psi #4-158psi #5-170psi #6-170psi #7-165psi #8-173psi. I bought the car a little over a year ago, and the previous owner said the engine had about 500 miles on a rebuild. He didn't mention anything about a cam change and I don't know if there was any head/valve work done. I'm going to see if I can find his e-mail and get a little more info. Thanks for the help.
Your compression seems OK. Did you adjust the air speed speed screws for best vacuum at idle. You will have to adjust the idle speed screw while doing this. Cheryl
valve problem Yes, when I set the mixture screws I set them at the highest vacuum I could get. The exhaust also stinks quite a bit which can be a little embarressing sitting in traffic.
Are you setting your timing with the vac advance disconnected? And are you attaching the vac advance can to ported or full vacuum? If it's hooked to full vacuum, then you may be getting too much advance at idle. ...hence the miss and the stinky exhaust.
valve problem I am setting the timing with the vac advance disconnected and the line plugged. The vac line is coming from the carb so I assume that means ported?
exhaust smell When you say stinky exhaust, I am thinking 'rich' smell. also a miss at idle coupled with a rich smell would indicate the possibiity of fuel dripping into the intake from a internal leak in the carb. mabey a high float level also.
Did you change? You did not mention plug wires and distributer cap..did you change these? I also had a similar problem on one of my cars..turned out to be a vaccum canister needed replacing. Good luck.
Didn't the nailheads come from the factory with manifold vacuum to the advance cannister? The initial timing is 2.5* With the vacuum advance hooked up, advance at idle should jump up to 18-20* If the advance unit is hooked to ported vacuum, the engine will not want to idle in gear.
valve problem I have the metal plate between the carb and manifold but it is one I made up from a piece of stainless steel. I have checked the float levels 3 times and they are set to spec according to the manual. I have replaced the dist cap but not the wires because everything I replaced looked almost new. Larry, I am getting 18-21 with the vac advance hooked up, but 18-21 is where my gage needle is bouncing.
18-21" of vacuum is excellent vacuum so you don't have a vacuum leak. Is the gauge fluctuating between 18 and 21"? If so, you may have a sticking valve. What I was talking about is your vacuum advance on the distributor. There are two kinds of vacuum, ported and manifold. Your vacuum advance should be hooked to manifold vacuum. When you disconnect the hose from the vacuum cannister at idle, you should feel a very strong vacuum at the tip of the hose. If you don't feel anything, the hose is hooked to ported vacuum. You need to switch that. Ported vacuum is near or at zero at idle. It rises when you open the throttle. When you hook the hose(with manifold vacuum) to the vacuum advance, the engine RPM should rise. If it doesn't, the vacuum cannister may be bad. At idle, with the vacuum advance connected, your timing should be at 18 degrees BTDC or so. With it disconnected, initial timing will fall to 2 1/2 degrees. I'm not talking about your 18-21" of vacuum, I'm referring to your timing in degrees.
valve problem I have checked the timing again and it is 2.5 degrees with the cannister disconnected. I have no way of checking the timing with the vac. advance connected as the marks don't go that high. I have duel exhaust that runs straight back to the mufflers(they're not joined anymore) and I noticed white puffs of smoke coming out of the right one every couple of seconds. Would this plus the bouncing vac. reading indicate a bad valve on that side of the engine? Thanks again for the ideas.
Point the timing light at the marks when you reconnect the vacuum advance. Does the balancer mark move up and out of sight? Is there vacuum from the disconnected hose?
valve problem yes there is strong vac from the hose and when i reconnect the vac hose the mark moves down to what looks to be @ 20 degrees btc.
fluxing vacume Take a hard look at your valve gear. Start with the pushrods, look for bent or broken. rocker arms, look for the hardened tips broken or missing. valve springs, look for broken. cam, look for wiped out lobe. lifters, look for cupping and wiped cam lobes. Any unusual noises???????
That is what I wanted to know. If the vacuum gauge has a regular downward spike, one of the valves is sticking./ Do what doc says, look at the valvetrain for anything obvious.
valve problem Okay, this is where I thought I was headed from the start. I thought I might have been missing something as far as the timing or vac went but I guess not. Thanks a lot for the help and I'll haul the valve covers and have a look. I'll let you know if I find anything.
valve problem I pulled the valve covers and rocker assembly. Everything on the rocker assy looks ok but I haven't taken it apart to look closely. None of the valve springs look broken. there are 4 pushrods that have thicker shafts and the ends have more of a round ball shape to them than the other 12. They seem to be newer than the rest with less wear on them. Two of the pushrods have obvious wear on the ends. One of them has a lip with a sharp edge where it sits in the lifter. These two are among the thinner/older looking ones. I am trying to avoid removing the intake and heads if possible. Could these pushrods be causing my problem?
