1970 Buick 455 I purchased 2 months ago. Since I picked it up it idles poorly, low vacuum from carb while trying to tune (about 14 lbs Mercury) I tried a general tun up with no luck. replaced points/condensor, dwell perfect, set timing 8 degrees, new plugs and wires still no help. Added a brand new stock qudrajet carb and still no change. Added HEI pertronix ignition and now added a new problem of large hesitation while acceleration. Tried multiple weights on distributer and switched to manifold vacuum and back to ported and the engine does not respond to any normal tuning specs. I have to run extreme advance timing with some spark plug ping to be able to idle when in drive or reverse. I brought it to a local shop that works on classics and older cars. They tried to tune and told me, I have got it as close as anyone can to running normal. They think that the cam shaft was installed a couple of teeth off or something else in the engine is not built right because it does not react the way it should. They had their entire crew agree that it has an internal engine issue. I thought it was possibly a vacuum leak, but the garage says there is none and I am wrong. Any help would be appreciated.
With 14" I wouldn't think of a vacuum leak. I have large cams in my.motor and they idle at a steady rpm but only have 5"or so. Its not crazy hard to pull the timing cover and look at the cam marks to see where it is
All indications from my observation is this is a stock motor and should pull 17 to 21 in of vacuum. I get a bigger cam would change that, but I just am using my old school logic for tuning of a stock motor. Totally confused and now a garage who works on classics is stumped also.
Well to me if the basic tried and true doesn't work like it should there is a reason. Time to roll the sleeves up and find out why. You can drai. The coolant from the block and have the timing off in a little over an hr I'd guess. Its an easy check and the gasket it like 13us bucks
True, I was surprised that the garage gave up so soon. They state that they are 8 weeks out to get into an invasive engine job that would leave my car there. This is the world we live in today.
One of those self re-profiling camshafts? Flatted lobes can make tuning a bit of a chore, and can result in poor idle, with low steady vacuum. (since we're guessing and not pulling parts)
"Added HEI pertronix ignition and now added a new problem of large hesitation while acceleration." Without wearing out my shotgun, might I suggest another distributor? You've got to do something about this anyway...
When I read this I was thinking cam timing (and/or jumped a tooth on the chain). You don't mention how long since the motor has been rebuilt, but my psychic vibes are telling me to start looking at things like the cam and timing gears/chain. Hopefully I'm wrong and something in the distributor fixes it. -Bob C.
My pet peeve is when guys quote initial timing. That tells you absolutely nothing since timing should change the instant you go above idle speed. My only thought is an ill fitting intake creating a vacuum leak into the valley. An engine with such a vacuum leak will require extreme advance to idle. Pull the PCV valve out of the intake, and plug the opening. Pull all the vacuum lines off the intake and carburetor and cap them. Run the engine and check for crankcase vacuum by putting a piece of paper across the oil cap opening on the valve cover. A stock engine should make 20" of vacuum at idle, fully warm, in Park.
Thanks for all the feed back from everyone I sincerely appreciate it. Based on the input I am going to have the car garage change the intake manifold gasket while closely looking at the manifold as a possible culprit. I have also read that if the previous builder matched the wrong intake to the block there could be issues like this. I will be more looking for cracks, warped or bad gasket. There is a peculiar hot spot about the size of a silver dollar where the exhaust flows through. (see photo) The spring controlled baffle for the exist manifold is gone, so it should not have ever gotten this hot IMO.
Actually it is pretty common for the intake to burn the paint in that area. While you have the intake off, you can plug some or all of those passages.
Drop the exhaust pipe and make sure that "spring controlled baffle" you referred to is completely removed and none of it got down into the exhaust pipe. Put a leaf blower to the exhaust pipe and check for big air flow toward the exhaust manifold. Some exhaust pipe of that era was double layered and the inner layer would buckle inward and seriously block the exhaust flow, causing stumble on excelleration and big power loss. This happened to me at the flattened area at the cross member on one side and the first bend past the manifold on the other side. The outer diameter of the pipe looks perfect and the damage is all inside. When I decided that was the next place to look for my drivability problem, I got out my cutter and started slicing pipe into 2-3 foot sections and bingo! Installed new 2.5" solid tubing exhaust.
I will definitely check that. Was the spring exhaust valve outside of the header manifold? Or was it inside the header manifold. I did not get a clear understanding on line.
