mais18

I have my Oldsmobile who acts up to 55 milles constant speed ( and good straight line ) it grazes slightly and when I release the accelerator revving the levels of the pot,
otherwise impeccable city and winding road.
This is an L6 1949

I have set the ignition by a pro


Thank you for your help


I speak very little English

47 Convertible

Does the car act up from 0 to 55 or not until you achieve 55 miles per hour?

Grazing is not a common term for car handling here in the US. I'm guessing you mean it varies from a straight line and you have to steer it back to a straight line. If so the cause is most likely a front suspension and steering alignment problem. The fix is a front end alignment. Replacement of worn parts may be required to get the alignment back to factory specifications.

Again, I don't understand what you are describing when you write: "revving the levels of the pot."

Releasing the accelerator should decrease speed and lower engine revolutions (RPM). Under certain conditions of decreasing speed and rpm, a weight shift can occur putting more weight on the front suspension which could cause slight and correctable steering changes.

It is very typical for cars from the 1940s and 50s to wander a bit requiring the driver to make almost constant small steering corrections to keep the car going straight. Bias ply tires can contribute to this and so can roads that have heavy wear causing slight grooves about the width of tires. But generally it is the wear of suspension and steering components.

You don't notice the phenomenon on curves because the steering is always under tension and any looseness is taken up by the turned steering. Likewise in the city speeds are usually slow so that wandering is not noticed plus you are stopping, starting, changing lanes and turning onto other streets so the car has no opportunity to wander.

Please write again if I am not understanding the problem. Everyone here is helpful but most of us are not professional mechanics and it may take a few tries before we understand your translated terminology. Keep trying, eventually we will help you solve this. What is your native language?
Jerry

DFitz

I'm wondering if he means the throttle is sticking.


If that is the case, very simply, some spray lube should do the trick. Mine used to stick a little. Spray the 4 or 5 linkages that end at the carb. Also, the accelerator pedal has a ball on the back side that may be sticky, spray that with some silicone spray, That will help.

oldcutlass

I'm thinking he means surging. What are the tuneup settings of your engine? Is the carburetor dribbling fuel while looking in the throat while its idling? When is the backfiring happening? Is it backfiring out the exhaust or carb?

jaunty75

I think he means just what he says. The car likes to stop by the side of the road every so often and eat some grass.

47 Convertible

Maybe because its an Olds and not a Pinto or Mustang?

Sorry Mais18, we're not making fun of your problem, just having a little fun with the vagaries of the English language.
Jerry

jaunty75

It IS funny.

I think that you are right about what he means. The car doesn't easily hold a straight line, at least by the standards of modern cars, so he's always having to make steering adjustments just to keep the car in the center of his lane. That's what "grazing" is. Wandering aimlessly around.

Depending on the severity of the problem, it may just be normal for this car and he's just not used to it. Or, it could be bad enough that it needs to be looked at.

B964

I think grazing may be what some techs (and some GM literature) would call "fish biting". A slight surge/stumble at cruise speed. Like the feeling of a fish hitting bait but not yet really grabbing it.

mais18

hello

I will explain my problem a little better

when I drive my car is 55 mph misfire and when I removal the foot off the accelerator that make a noise levels of exhaust.


another question. I want to adjust the valves , should we change the valve stem must

thank you

47 Convertible

Salut mais18,

Your second explanation is much improved over the first and the only question about the misfire is whether it occurs only at 55mph or begins at 55 mph and continues at higher speeds?

Does the exhaust get louder only at 55 mph or does it begin making a noise like pop, pop, pop as the engine misfires?

When adjusting valves there is generally no need to change what we call the valve keeper. Oldsmobile calls it the valve key. I think that is what you are referring to when you call it the valve stem. In America the stem is the long, thin part of the valve and the large round part of the valve is called the head.

Be very careful when you take the valve compartment cover off that you do not tear the gasket as that would cause an oil leak when it was re assembled. I don't know if the gaskets are available but if not and you need a new one, it could be made from a sheet of gasket material which should be available in an auto supply store.
Jerry

mais18

mais18

hello

The misfire begin in 55 mph and the noise the exhaust is when I remove the foot of the accelerator

47 Convertible

________________________________________________

mais18 states in his first post on this subject the ignition was set by a pro. If we take this at face value and given the difficulty of translation from French (presumably) to English, I take that to mean its had all needed ignition components checked, replaced or adjusted so that would cover plugs, plug wires, distributor cap, rotor, points and condenser and ignition timing.

Of the big 3 to make an engine run that takes Spark out of the picture, for now, and leaves air and fuel.

Sufficient Air: Maybe dangerous to presume but I'm going to hazard a guess that the engine is getting sufficient air and that the air filter isn't totally plugged with gunk, is probably oil bath type but not over filled so that oil is being sucked into the carburetor somehow causing engine misfire.

Fuel: That sort of leaves fuel. Clearly its getting enough to drive well in the city and on curvy roads as mais18 states in his original post. I'm thinking these are conditions and driving that require lower RPM and thus less fuel delivery than driving 55mph and faster on roads that allow that. ( 6 cyl Olds of that era probably had the 3.90:1 rear end or the 3.63:1 which would mean fairly high RPM at 55 and over)

At the risk of over simplifying that would seem to leave possible causes as 1) partially plugged fuel filter or, 2) worn fuel pump or worn cam lobe that actuates the fuel pump, 3) poor quality fuel with water in it or just poor quality like very low octane or, 4) dirty or badly worn carburetor--maybe with high speed jet partially plugged? Seems to me any of these could cause high rpm miss.

I don't know what to think about the muffler noise when he takes his foot off the accelerator at 55+ mph. The first thought is just a worn out muffler making noise.

But its possible the muffler may be crudded up with years of moisture=rust and plugging so exhaust can't get through fast enough resulting in strange exhaust noises like a loud hiss? A partially plugged muffler might allow sufficient exhaust to not affect engine performance at lower rpm experienced in city and curvy road driving but cause back pressure issues at higher rpm of highway driving. Seems far fetched speculation on my part but plugged exhaust and resulting excessive back pressure might cause missing.

So what to do to fix the engine misfiring at hgher RPM/speed if its not electrical or air?My shade tree mechanic ideas. Now lets hear from the real mechanics on the forum.
Jerry

mais18

I'll watch it all

I would give you news

thanks

DFitz

My 3 guesses would be:
1. fuel pump
2. Fuel tank. If it is an original tank, possibly gunk in the tank clogging the screen on the fuel pickup. Possibly rust inside the tank clogging up the whole thing. Good analysis, ok at lower RPM, but not enough fuel at higher RPM. It does sound like clogged fuel, or not enough.
3. There is also a screen on the fuel line inlet to the carb. Check that for being clogged.