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Rough '64 Riviera


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Since I bought my Riviera about 3 years ago I'm not quite satisfied with the way the engine runs / idles.

It's kind of rough so to say. When I compare it to the 350 in my '68 LeSabre, quite a difference. That 350 purrs like a kitten, doesn't miss a beat.

I've never driven another 64 Riviera with a 425 since they are kind of scarce around here. Heard one run at a meeting a few months ago, and it idled so much smoother than mine.


I was told the engine was rebuilt at some time but that doesn't mean anything. I know there are people that rebuilt an engine with a brush and spay can.

Here are the things I already did to the engine;

New plugs,

New wires

New rotor and distributor cap. Eventually I swapped the points for a Pertronix Ignitor II and flamethrower coil.

New timing chain

New rebuilt carburator (AFB3665S) 


I thought of a vacuum leak but couldn't find one. So I took of the big vacuum hose that starts at the back of the intake manifold and plugged that connection. Thinking that if there was a vacuum leak causing this rough idle plugging that connection on the manifold would take care of this. It made no difference. Correct me if I thought wrong.

When I bought the car it didn't have a vacuum reservoir, they just connected the hoses where they normally are connected to the reservoir. I bought a reservoir last year and it didn't make much of a difference.


Checked the balancer if the outer ring hadn't moved. No, still in the right place.


Now I'm thinking that, if the engine was rebuilt like the seller said, they maybe put in another camshaft that's causing this. But that is not so easy to determine I guess.


Any thoughts on this one? Did I miss something, do something wrong, things I can do, ...... you know. I'm running out of ideas.


Attached a picture of the camshaft I took when changing the timing chain.




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Before assuming you have a vacuum leak it is critical to know that all 8 cylinders are contributing. Isolate each one of the cylinders by cancelling each spark plug. You can pull the wire away from the plug while the engine is running but the "proper" way to do this is to provide an alternative ground instead of the spark plug. If, after pulling the spark plug wire away from the plug, there is no change in the idle RPM that is an indication the cylinder that is cancelled is not providing any power. After you are satisfied each cylinder is mechanically sound move on in the troubleshooting process.

  Tom Mooney

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Well I checked the spark plugs by pulling the wires, they all perform like they should.

Did a compression test, the lowest was 170 and the highest was 180 PSI.


Checked timing (again), 2.5 BTC without vacuum, 30 with vacuum.

RPM in neutral 820, RPM in D 580

It idles rough when it is in D (so at 580 RPM), when it is in neutral it's fine.


I did notice that the timing mark on the balancer is not really steady. It kind of jumps back and forward. Also the RPM's when idling in Drive is not consistent, it kind of varies from 570 to 590.


Maybe a worn distributor bushing or gear??


Checked the idle mixture screws. No matter what I did, turning them in or out, the RPM would drop, so I guess this is the best mixing ratio.  


Just came back from a local cruise night and noticed that after driving the "autobahn" for some time the engine tends to stall when I would stop at the end of the off ramp. It doesn't stall but the RPM's drop until the oil pressure light comes on for a short time (just flickers) and then it recovers itself.   


Oil pressure on the freeway is around 40 psi, 20 psi when idling.

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My '64 had an untenable slight  roughness to it and I had checked all the typical tune up and carb things pretty much the way you have. It seemed to run good but not quite right. I ended up with a piston in pieces in the bottom of the pan. I have seen two other 401-425's break or crack pistons. That was about 14 years ago and those engines are getting older. I would do a minimum of a very thorough leakdown test. It looks like you don't have a problem opening the engine yourself. If I experienced the same situation I would probably pull it down and check the pistons. Sounds like a lot of work but sometimes you have to do it.



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One thing that MANY forget is that, many cars, the vacuum advance post had a rubber bushing on it that limited the amount of travel the vacuum advanced. 30* is TOO MUCH. Should be more like 20*-24* MAX!!! with the initial being set to 2 1/2*.  Guaranteed this rubber limiting bushing has fallen off/deteriorated from being 50+ yrs. old. One thing you can do to check that doesn't cost any $$$ is to retard the initial timing to about 6*-8* retarded & then hook up the advance to see if it runs any smoother. Will ALMOST guarantee it will at .



Tom T.




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@ Bernie.

Don't hope I have to go that far to get this solved. Is one of my last options.


@ Tom.

No play in the distributor shaft whatsoever. Took of the cap and tried to wiggle the rotor. Nothing.  Maybe worn out gear? 


@ Tom T.

That's an easy thing to check.  Maybe I even used the wrong springs for the weights, so I get some  centrifugal advance also.

Going to check that as soon as I get a chance. Any idea if those bushings as sold separately or do I just make one myself.


Going to let you know if playing with the advance makes any difference.

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Mechanical advance should NOT start before 650-700RPM's or so. If it does the springs are TOO light. Some replacement vacuum advances used to come with a rubber bushing. I haven't seen one come with one for awhile now. Make one out of a piece of plastic.

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OK Riviera People: My car was running rough too. It felt like a vacuum leak.  All the diagnostic tests were performed and negative.  Them Wally got out the atomizer.  The a/c vacuum lines were all leaking ever so slightly under the dash and console.  He suggested replacing them and test again. On the second test he hinted I might expect a leaky booster. Yup, coming in from under the dash.  Fixed'em and she is as smooth as a late lo mileage fuel injected car. Old cars...I thought the metal grew back.



My wife loves it!  Mitch.

Edited by lrlforfun (see edit history)
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Haven't really had time to get into this.

I fiddled around with the vacuum advance, and yes this made an difference. But not in the roughness in idling. Really hoped it did because it would be a simple resolution. But I hadn't had a chance to really test it. It startede raining and when the raining stopped I promised my wife and kids to take them on a vacantion. 

So as we speak I'm staying at a campground in Luxembourg. No so bad, but I'm not able to look at the possible causes/ solutions mentioned by you guys.

When I get back home next week I continue my search.


I did notice I had some play in the distributor gears. Is this just a matter of changing the gear on the distributor shaft for a new one (if they are available?)?






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