318 Poly shakes like a wet dog

[Dave145]

Howdy everyone! Some of you may remember me as the unlucky member with the vibrating '64 Polara. I finally got that sorted out (new rims and tires cured that!), and now it's time to address some other issues. The main one is how this thing idles. I've got the 318 Poly in my car. It was originally a 2bbl. I picked up a nice 4bbl cast iron manifold last fall and finally installed it right around New Years. I topped it off originally with an edelbrock 1406 carb and let it be. It never really idled right then either, but I figured it was just the edelbrock carb that had been sitting on my shelf for a couple years.

So fast forward to now. I got rid of the edelbrock and in its place installed a Summit Racing 500cfm carb. Vacuum secondaries, electric choke and all! It idles better, but still pretty poorly. It goes down the road great, however. I have zero complaints with that. Even the fuel economy has slightly improved. I've adjusted the timing, adjusted the valves and adjusted the carb and I still havent gotten it much better. It used to idle okay with the 2bbl on it, so I'm not sure why it wouldn't with a 4bbl. Here's how it sits today:

- Vacuum is steady but low. 15"-16" at the highest. I have checked everything for leaks and have found nothing. I plugged the vacuum advance hose and the heater control hose as well and that didn't change anything. Vacuum is taken from the base of the carburetor.
- My idle screws are turned out 1.25 turns each.
- My plugs are Autolite 85 plugs gapped to .35 as per my manual.
- My firing order is correct. I have chacked many many times.
- The timing is set at 14* initial. It does not idle any better down at 10* or at 12*. My mechanical advance is set to 28* to give me a total of 38*.
- I have dual exhaust on my car with an H pipe. 2.25" pipe all the way back
- Valves are adjusted on the loose side at .13 and .21. At the advise of someone else I tried .10 and .20 and that almost made it worse.
- I added electronic ignition to the car when I first got it. Spectra Premium distributor, and multiple different ignition modules. None of them have changed how it idles. The first one was a Standard box. It ran okay. Then it randomly started taking forever to crank and eventually died. The second was a box from my nearest Mc.Parts store. It works pretty good but starts to get goofy when warm. The third is currently in the mail and will be the blue box off ebay from Rick E.
- I have the cut to fit Accel plug wires. 8mm. They are all nicely seated on my cap and plugs.
- I have an Accel SuperStock coil. Specs line up with a stock Mopar coil. For grins I swapped it out with another one I had laying around, but it still runs the same.
- I do also run a ballast resistor. It is a 1.2 ohm. It was the one that came with my conversion kit. My spark is still BRIGHT blue/white.
- My balancer is original and has not slipped. I have verified the timing mark on the balancer with TDC.
- Timing chain is pretty new as well.
- The motor and trans munts are new within a couple years. The motor mounts are just whatever brand the parts store had and the transmission mount was bought from Joe Suchy.
- The motor has never been rebuilt or gone through. The heads have never been off. The cam is original as well. It used to run and idle okay, but now it just doesn't want to.

The car shakes like a scared chihuahua at idle. You'd think it has a radical cam in it. The fenders shake all over the place rhythmically side to side. You can even see the shaking at the rear of the car as well. The exhaust STINKS. It smells worse than a fuel injected car. The exhaust shakes around a good bit as well. It does this when it's warm, cold, wet, dry, uphill, downhill, in the rain, on a plane...you name it.

Part of me wonders if I have an internal vacuum leak under the intake or something stupid like that. This ain't my first rodeo, but this one sure is kicking my ***. I'm all for my car shaking at idle if it's got a big nasty cam in it, but this is ridiculous!

 

[Jerry Hall]

Just going on what I am seeing you post in sort of a common sense look. You said the problem started with the addition of the 4bbl intake and first carburetor. Now you have changed to another carburetor with only minimal improvement. My gut is telling me a vacuum leak and intake related. Have you tried spraying carburetor and choke cleaner around the intake to see if there is anywhere where the engine smooths out. I have never been inside a 318 poly, so I cannot relate to an internal vacuum leak. My guess is still an intake problem of some sort.

 

[steve340]

How did it idle/run while it had the 2 barrel on it?

 

[toolmanmike]

You should also do a good compression test to make sure you don't have a weak cylinder or two. A leaky/burned valve will make it shake like a dog poopin' peach seeds at idle and will almost smooth out at 2000.

 

[Dave145]

Prior to the 4bbl manifold and carb swap, it was hit or miss for how it idled and drove. As a 2bbl it had multiple different carbs put on it (couple BBDs and a couple Strombergs) and it always seemed to run decently. It just had no power.

I suppose thinking back what had the biggest effect on the cars idle was the H pipe. Originally I had regular dual exhaust on it, but after I broke a weld on the driver's side pipe my exhaust guy added the H pipe to strengthen it up. Ever since then the car has been a bit touchy with it's idle. Maybe a coincidence or not. I'm not sure. Thoughts?

I have ordered a new intake gasket set along with the correct plugs for the car as well. Unfortunately I won't have them until Tuesday.

In the meantime I will do a leak down and compression test and report back. I'm hoping not to have any bigger issues with the motor but I guess we will find out!

When I pulled my plugs today I did find that one of them (#8) was lean. The plug end was white and powdery. I'm thinking that's my problem cylinder.

 

[Belle66]

Double check the firing order and the spark plug wire placement. Pull the distributor cap and got to #1 cyl at TDC. Look at where the rotor is pointing and go from there. I accidentally swapped 2 locations, got a lean cylinder and a shaky engine.

 

[Dave145]

I've gone around and around in the firing order a couple times today alone (namely because I'd lose track of where I was in the line up!). Going off of my sun sheet from 1964 I have it correct. But I'll certainly give it another look!

 

[Belle66]

Its possible that the distributor is not installed at the factory location...which is ok as long as you adjust for it. That poly is a tough motor, pretty sure you could swap 4 and still get it to run. The key is to use the rotor position and line up #1 plug wire to that.

 

[Dave145]

Well I have no problem checking it again!

I'm hoping the one lean plug I've got on #8 is just an internal intake leak and not a burnt valve.

 

[matthon]

Sounds familiar, except for the part where you added a 4 barrel.

I had a vibrating poly, there were a few other issues that hit during the same time which made it maddening to say the least.

Bottom line, brand new engine mounts, which showed zero signs of being garbage.
I put 1 rock hard old mount back in and removed 95% of the vibration.

I went with an msd early on and it has been great.

https://www.forbbodiesonly.com/moparforum/threads/318-poly-vibration.165145/

 

[Dave145]

I'm glad you chimed in! Right before I posted this I was reading your thread. Seems like you kind of chased the same things I am. I wish I kept my old hard mounts just to see if they'd change anything.

 

[khryslerkid]

My idle screws are turned out 1.25 turns each.

Use a tac or vacuum guage and get the highest rpm out of each screw. Then turn each back in 1/8 to 1/4 turn. Same with your timing, get the highest rpm then back it off a couple of degrees. If it pings back it off a bit more. Factory settings are a base line. Each engine is a little different from one to the next on what they need to run just right.

Checking for a vacuum leak is a good idea also. When you are adjusting the needle jets on the carb and it's not making any noticeable difference, it's a good chance there's a vacuum leak.

 

[BB BELLA]

check the carb float levels and intake sealed 1st.
I'd be confiming cam timing and all rockers are lifting #8 in particular! if the exhaust tube made that big of a difference something in the breathing isn't right!
do a power balance pulling one plug wire at a time looking for the ones that make little difference in rpm when removed!

 

[peabodyracin]

This will sound off the wall but I wanted to mention it. I had one years ago that would idle very rough and smooth out pretty well when you drove it, although it never seemed right. It was an effort to get the car to highway speeds. I don't recall a bad exhaust smell though. I bought the car cheap because the previous owner had given up trying to sort it out.

Anyway, after days of fighting with it I discovered the harmonic balancer was failing and actually moving around (rotating) on the crank snout. I've never seen or heard of another one doing this, and still don't know why it happened, but a different balancer cured everything. The partial rotation on the crank would affect balance and timing adjustments when using a timing light.

 

[Dave145]

So far I have adjusted the carb by both ear and vacuum gauge. Turns out it was pretty much spot on! The highest vacuum I can get out of it is 16" on a dry day (if its humid then forget it).

I have sprayed all around the intake and carb with brake clean (the flammable kind) and found nothing. I sprayed both ends of the intake as well and found nothing there either. I disconnected and plugged all vacuum connections coming off the carb and that didn't change anything either.

I will recheck the valves when I do my compression test today and report back. .

I have checked my balancer to make sure the timing mark is on in the last and it has been. I will triple check today again just to be sure.

 

[Demonic]

Compression test, then if one or more is low a leakdown test.

 

[Ron H]

There are several tests you can do with a vacuum gauge and inserted a link that offers just some general info though you can google for more pin-point information. I had a problem with a valve in my poly before I ended up totally overhauling it as I planned to do anyway. On that cylinder the vac gauge went nuts and factored it might be due to carbon build up. The odor/smoke you find indicates a problem of course and possibly if the motor hasn't been cleaned carbon build up could be a gremlin. Assume you don't find any contamination in the oil or coolant. I ran the old mystery oil in mine for a good 500 miles and that helped quite a bit though there are other cleaners such as sea foam you can run through it right away for clean out. Might not be relevant; but tossing out ideas...especially if you haven't done a motor flush.
https://itstillruns.com/erratic-fluctuation-vacuum-gauge-during-idle-12227649.html

 

[Dave145]

Well guys I think I found the issue. The odd part would be what caused it.

So today I went out and did a compression test. All the numbers came back low, but still all well within each other. All cylinders are right around 90psi. I checked them both wet and dry just to see if I had a ring problem, and that didn't change my numbers a whole lot. When they were wet, they were all right around 95 psi. Two of them came in at 100psi when wet.

Then I moved on to a leak down test. I figured I might as well while I'm here. Two cylinders (5 and 7) leaked a tiny bit of air out the tailpipe. All the rest seemed to be fine and I didn't hear any escaping air.

I then went ahead and triple checked the firing order one more time. It was fine. #1 wire on #1 on the cap. All my plugs seemed to look even after I let it idle a good bit yesterday as well.

Last thing I could think of was to recheck the valves. We adjusted them last July to .13 and .21 HOT. Today, they were a mess and all over the place. One of the intake valves was all the way down to .08, and one of the exhaust valves was all the way up to .25. I have no idea why or how they changed this drastically in only a few thousand miles. Starting to make me wonder if the seats are getting pounded to oblivion since the heads haven't been rebuilt and I'm obviously not using leaded gas.

But either way now with the valves sorted out again it runs much much better. So much smoother at idle and really has some excellent power off the line.

 

[BB BELLA]

if your happy with the drivability now you've accomplished what you wanted, it may get better with more miles. high mileage engines sometimes develop a groove in the guides/stems stopping the valve from rotating allowing deposits to build. the loose valve now lifting more may have a chance to rotate and possibly shed some more combustion deposits. you could try the old coldwater ingestion trick! get the motor completely warmed up,give it a little rpm maybe 1500 and spray some cold water in the carb. sometimes that will knock carbon out of the combustion chamber!

 

[Don Frelier]

Did you repeat the compression test after adjusting the valves?
90psi is pretty low, ok crappy.