1976 02: Shakes violently at 800rpm idle

[ramayah]

Vibrates as if possessed at 800 rpm. By increasing the idle at say 1200-1300 rpm. it calms down and runs smoothly but too high for comfort.

It's has 32/36 Weber carbs.

I really need your help and advice on how to rectify this problem.

[MAD02]

I had a similar problem with my 76. It was the transmission mount. It had broken in two. Also check the engine mounts to see if they are in good shape. Good luck.

David

[ramayah]

thanks David.

I'll check it out tomorrow.

randy

[wegweiser]

Perhaps you're only getting fire, air, and fuel to 2 or 3 of your 4 cylinders. I'd pull plug wires one at a time (carefully - ZAP!) to see if one or more of the cylinders is dead (ie: no change in idle quality).

could be:

a) bad plug wires, loose ends

fouled plugs

c) bad head gasket (especially if two adjacent cylinders are dead)

d) broken rocker arm, not opening valve

e) cracked distributor cap or rotor

Tired or broken mounts will also cause shaking - how's the drivaility and engine performance above 1800 rpm while moving? If it's fine - check for absence of ignition (spark) before tearing into carb or distributor/ignition timing.

Hope dis' heps!

Paul Wegweiser

"...heeeere kitty kitty kitty...."

[Chris_B]

Paul covered most of the potential causes for this problem, but you didn't provide any context. For example, did you inherit the car in this condition? If not, did the probem develop suddenly or over time? The solution could be as simple as adjusting the idle mixture. If the cause is not obvious after doing the check Paul describes or inspection of the plugs/wires, a compression test would provide a wealth of info about whether you are dealing with a sound platform.

Also, just eyeballing the plugs will be informative. Does one look different from the others? If so, suspect that cylinder as the potential cause of your problem.

[ramayah]

Thanks Paul for your advice.

The car runs great at highway speeds. A few months ago I replaced plugs, wires, coil, cap and rotors and it was idling fine. However, after sitting for a while without driving it and now I took it out it started giving me this problem. I'll pull the plugs and checked them for fouling and replaced if needed and see if I have better results. If not I'll check the mounts etc.

PS.

If the plugs are fouled what do I do then to keep them burning clean. And what would have caused them to foul. It's very possible that this might be the cause since it did not vibrate when I replaced the plugs some months ago.

Randy

[ramayah]

Thanks Chris.

When I got the car 12 years ago It never gave me any problem. But over the years and not much driving it started developing hard starts and rough idling etc. Most of the time it sits in the driveway. Many times I changed the plugs because they are black soots on them. I didn't realize that the bad plugs could have caused the vibration. I will re-time it, fool around with the idle mixture and so forth and then it will start to idle normally again. time time it's really bad and I'm about to give up on it.

Anyway, tomorrow i'll check the plugs and report back to you kind people.

I apprecaite it.

Randy

[Chris_B]

From what you have said, it sounds like one cylinder is not firing right, so that would implicate a mechanical or ignition problem with a cylinder. Another problem with cars that sit for a long time is the buildup of shellac in the jets from deteriorating gasoline. You could have a partial obstruction in the idle circuit of the carb.

Black soot on the plugs generally indicates over-rich mixture, if you are talking about fluffy soot rather than oily soot. The could happen if your choke is not properly adjusted. Have you checked to make sure it is open all of the way when the motor is warmed up?

Timing generally doesn't go out of adjustment absent some cause. The most common cause is changing point adjustment, caused by point block wear which changes the dwell.

[Guest Anonymous]

as everyone has said, it sounds like a really bad misfire and maybe bad motor mounts. But never underestimate the effect of loose flywheel or clutch componants. Remove that bottom inspection plate and make sure that your friction pads are inplace and the bolts are all there. Just a thought.

[c.d.iesel]

remove carb top,

clean float bowl, clean all jets,

remove and clean idle jets on side of carb,

replace all tiny o-rings,

adjust dwell & timing

adjust idle mixture and idle sped

adjust valves

quality of gas ???

.....and any or all of the above aforementioned stuff

[Guest Anonymous]

replace all tiny o-rings,???

Besides the idle jets, what o-rings are you referring to?

[Arshloch]

Mine does it after sitting for a long time,hence the aforementioned build of crap in jets is the cause (it clears after some hard driving). And the mounts are pretty soft too! I would replace the motor mounts if they seem to be tired and rebuild the carb, plus tune the ignition seem up.

Also check for vacuum leaks. Sometimes the carb body bushings wear out (literally causing a vacuum leak), making it hard to adjust to lower rpm speeds.

[c.d.iesel]

a car with krap motor mounts

does not shake at idle if the motor is runniing FINE .

[ramayah]

I checked the plugs and all are firing fine. I believe you are right; the carb needs rebuilding. I'll find a good shop and have it rebuilt or buy one on ebay. Meanwhile , I'll run it hard for 30 miles or so and see if the shakes go away.

the mounts are good and don't think it's the problem.

Thanks to all you kind folks.

Randy

[Hammer03]

While you're in there it would be worth doing a compression test. Mine exhibited the same symptoms and had blown the head gasket between cyl 1 and 2. Should be worth the few minutes it takes for the peace of mind to know that isnt it.