340 vibration and hesitation with a short history

[Rockboyz]

Hey fellas! I know that trying to explain and rectify problems over the computer are almost impossible, but I'm looking for some areas to start looking at, with these two problems.
Car history: 1972 Challenger. Owned the car for 33yrs. My first car. 70 340, Edelbrock performer, Holly 750 vacuum secondary.727 / B&M shift kit, 3:91 rear.  Motor was put together back in the 80's by a buddy of mine, which at the time, we were kids. Not sure about all the specs, but I believe it has a "Fireball" cam, if you guys remember those. lol! Has a nice sound at idle. Anyway, I was never really mechanically inclined back in the day, but over the years I have become more fluent with engines. Mostly with snowmobiles, quads, and bikes. rebuilding them, dialing in the carbs, ect...
Since the early 90's the car has really just sat in the garage. Occasionally a start up and back out, but that's about it. Cant have more than 5000 miles on the engine. Marriage, kids, sports, divorce, ect...no time for the car. So around 2001, I had a reputable local guy do a tune up on it for me. Car ran great! break the tires loose, chirp second, fun stuff! But that has gone away. Now that my boys are grown, and my oldest is playing with these rice grinders with coffee can mufflers, I have got the passion and the bug back to start driving this ol hot rod again (maybe).
So here are the two issues:
1) Hesitation off the start, checked the squirters and looks like I'm getting fuel as soon as I touch the throttle. Maybe to much fuel now? Not enough air?
2) Vibration is engine only. Not driveline. I would say 1500 rpms and up. kind of has a wave type / feeling or sound to it. Again, hard to explain, but somethings not right. interior shakes. Thought maybe a miss, so I pulled all the plugs. 1357 have a light tan color to them, 2468 a darker milk chocolate color, which doesn't seem right.
Lastly, I can hear at higher rpm under load a bit of a "knocking" sound. Maybe a bearing?
So if I have a bearing going internally, could that be causing the vibration coming and going like I described?

As always fellas, direction and comments are much appreciated!!!!
Many thanks in advance!!!

[734406pk]

Cool story! Welcome back!
 
 First thing I would do is take a compression test on all cylinders and record the readings. If all good there, tune up replacing Distributor cap, rotor, spark plugs and plug wires. Check your base timing and confirm that the centrifugal mechanical advance is working properly. The vibration you feel may be a dead cylinder i think. Good luck and post back your findings!

[Cazbah362]

Rock - Here are a few things:  Timing sounds in question, under load, higher RPM and the initial stumble as you described is why I would say that.  Also, you may have some fuel issues, meaning old fuel or low octane fuel.  What is your oil pressure? 

If it where mine, first thing I would do is change oil to full synthetic and to a Wix filter - low cost, engine has miles - not sure on oil pressure.

Next, put some good fuel into it - old muscle seems to respond to this.  If your not running a wideband, I would use 5 gallons of high octane leaded, topped off with just good ole 91 - again, good, cheap (low cost) and easy

Next I would check fuel pressure / clean filter and plug wires (tune-up)

Then sit down and set timing - I am an all in guy (36-39) depending, but I would suspect you have vacuum advance and non double pumper.

If you still have the issues, a leak down test would be the best way to begin checking for health of motor.

Also - if you have a automatic, also check your convertor to flex plate bolts - they loosen and sometimes sound like a rod knock

That is my shade tree advice - and I love those old Fireball Cam's - takes me back to being a kid -

Good luck - traction is your friend when running those little fart cans-

CP
   

 

[xtopfuel]

also check the flexplate, if you have a knocking and vibration its possible the flexplate cracked/broke unlikely a bearing will give vibration, tan odd bank chocolate even bank a simple a/f trim out

[Rockboyz]

This is Great!!!! Love this site!! Thanks Guys!!!!
Oil pressure good! just changed oil and filter
New fuel, 91 octane...may need a need fuel filter.

I'll report back as I go...

[cudabob496]

ya, get all the basic tuneup stuff out of the way first, before diving in.
ie plugs, wires, dist cap, timing, and rotor, etc.

[MaxwellW]

Great story. My dad had a 1970 Chrysler 300 and I would love to get my hands on one someday.  Best of luck with your maintenance and getting it up and running again.

[jimynick]

Good luck with the vibration and I remember the Crane Fireball cams well and had one in my 68 340. As you say, a nice lope to the idle. 

[734406pk]

Good luck! I hope it's something simple!

[crash340]

Rock, drop the belts off your engine and start it up to rule out alternator/water pump and power steering if you have it, I had a vibration similar to your description and found the alternator was bad, as soon as I dropped the belts the vibration was instantly gone, I then put one belt back on at a time to check items

[73_Cuda_4_Me]

I also had a 'cycling vibration' on my 340/727... It was the kind that basically massaged you spine as you increased rpm up to around 3k... cycled about every 2-3 seconds... I had some rust issues on driver's front frame rail, so pulled engine/tranny over winter to fix... changed torque converter while out, and replaced LCA bushings, strut and sway bar bushings... have it up and running again, and it's smooth as silk now, and drives SO much better...

My vibration was present in neutral, so I'm confident mine was the torque converter (I found out it was actually a replacement junkyard 73 360 w/weight removed).

Make sure that flex plate and torque converter are 'clocked' per factory service manual, too... that is the only way the balance will even be close...

Terry (Tactransman) has thread in Archives on tranny setup, modification, and proper orientation... Kudos to him for all he did helping others here on this site (me included)...

[Rockboyz]

Thanks Guys!!! I appreciate the info! This gives me a lot to check!

[Bullitt-]

With the right bank plugs looking so different from the left my thoughts go to the heat riser valve in the exhaust manifold on the right side.
If yours still has one make sure it is opening or fixed to stay open. 

[734406pk]

With the right bank plugs looking so different from the left my thoughts go to the heat riser valve in the exhaust manifold on the right side.
If yours still has one make sure it is opening or fixed to stay open.

That's a good idea! especially since the car has been sitting for a while. the heat riser(if the engine still has one) could easily be rusted closed. High exhaust backpressure...

[Rockboyz]

Factory exhaust manifolds are gone...Blackjack Headers were installed back in the 80's!