Engine vibration/missing after hibernating 10 weeks
 

12a Stock
84 GSL
164k miles, engine rebuilt at 160k.

Stored in the garage Jan 1 to March 15.
Only thing I did this year as it was anticipated to be a short time was a can of Seafoam in a nearly full tank of gas.

It idles rough when full choked at startup, but smooths out as it warms up and less choke.
Usually a big puff of smoke when starting cold, much more than before, but does not last.

It is in the engine: at 4k on the highway I can feel the vibration, then in neutral without dropping speed, the vibration is gone.

It runs and acceleration is good. I don't see much difference, but it may be a little less performance, but that could be subjective memory.

Things done already:
Changed fuel filter. It only had 4k miles and 1 year of driving, but was yellow discolored.
To eliminate the obvious ignition factors: replaced plugs, dizzy cap and rotor. Verified correct timing.
I do not know the age of the ignition wires. Maybe 34k.
Coil resistance: Leading 7.68 k ohms, Trailing 6.68 k ohms.

Battery is now 7 years old. Trickle charged when in winter storage.

Fuel line from tank to filter had a slow driping leak at the fuel filter. The first 3/4 inch of the line was cracked. Shortened the hose and now no leak.

I've only run 2 tanks of gas through it so far after adding the Seafoam.

Question:
Could the vibration be a result of the Seafoam sitting in the gas tank for 10 weeks loosening up all sorts of crud that now is in the fuel system?

Or another cause I've not looked into.

Any suggestions would be most welcomed.

The next thing I'll try is a compression test, just in case.

Well, since putting it in neutral at speed caused the vibration to go away, I would
suggest ujoints on the driveshaft or something in the clutch area. Check the
ujoints since they are easy to see.

Seems like you have two issues tho; the vibration at speed and the complaint
about a rough idle when choked. I suspect you may have old engine-itis, the
seals are sticking a bit when cold and finally pop when it warms up. Run a bunch
of seafoam directory in the carb and drive it. Another option is redline the crap
out of it, maybe it just has carbon built up internally causing these issues.

Thanks.

I'll check the U-joints. That makes sense as the vibration is also more noticeable under load such as going up a long hill.

The apex seals & springs, side seals and springs were all replaced in the rebuild.
The apex rotor gap was within spec, but those are the original rotors.

Thanks.

Try rotating the wheels. I'm serious.

And I believe you.
Absolutely. That's would be the easiest fix.

Road test later.

The rear U-joint is solid, no free-play.
I'll need to raise the front end to get to the front one. It's not as easy as sliding in under the gas tank.

You are too sensitive Tim. A Worry Wart.

https://encrypted-tbn3.gstatic.com/i...LHvP3GYsOB6XJL

Just drive the damn thing and when it breaks, let us know.

We'll take it from there.

You're right Ray.

Its still a blast to drive.

Oh, I checked my trany in the 84 GSL, K 16682, not even close.
Searched the internet, found nothing.

Not quite broke, but not right either.

Start up: White smoke, but goes away. Not an oil burning smell.

Today, choke out: 2000rpm, drops to 1000, then back up again. Did that 3 times.
Happened last night at gas station. Engine warm. Started, normal idle, then dropped to 300, then died. Got home and it died in the driveway. Restart and normal idle.
Did the same thing last Wed at a drive through, but I kept the rpm's up until I got home, but then the idle was fine and I could not replicate.

I let it idle for 15 minutes, it keeps dipping rpm's down to 300 or so, then back up.

Still rough idle.

Could be an accessory, like an alternator or water pump issue or it might be the pilot bearing acting up.???

Swap your coil wires and see if it improves. Sounds like a coil/ignitor problem to me

I think you'll solve it, Tim. Once you've gone through every system and confirmed that they are all working, of course.

It runs worse today.
Had to go to the secondaries going up a steep hill to keep from slowing down, then it was OK again.

The trailing coil was replaced 32k ago as it was arching to the body and I failed the emissions test. The leading coil as far as I know is original at 164k.

I'll swap the coils and see if it improves.

Thanks.

[QUOTE=TimWilbers;12044331]It runs worse today.
Had to go to the secondaries going up a steep hill to keep from slowing down, then it was OK again.

The trailing coil was replaced 32k ago as it was arching to the body and I failed the emissions test. The leading coil as far as I know is original at 164k.

I'll swap the coils and see if it improves.

I.do think you should rebuild/clean that carb too. One of my carbs I was selling sat with the crap gas they sell now for 6 months, and now the metering block gaskets are leaking and the metering body itself is pitted. Did you run an enzyme treatment in the tank to keep the gas from breaking down?

Swapped the coils: no change.
Swapped the coil wires: no change.

I've never had a fuel pump fail, can it be intermittent in volume?

When I changed the plugs last week they were a light brown/tan color on the electrodes. After running today they were more black which was easy to wipe off.
Image of the same two trailing plugs before and after wiping off.

There is no noticeable drop in coolant level, and the intake manifold O-rings were replaced at the rebuild 4k ago. That might be the white smoke at start up. But this is a recent development so I would not see a noticeable drop and I would think it would be more continuously drinking coolant not intermittent.

There are no oil droplets in the coolant as there was when the engine failed before.

Gas line to fuel filter replaced, along with fuel filter.

Sprayed carb cleaner on the outside and inside.
Would a carb/fuel system cleaner in the gas do any good, or harm?

I do not know if the carb has ever been rebuilt. I know not in the past 10-11 years, 36k miles. It may have 164k on it.