1955 Eldorado - what's this exhaust noise?

[Lockhouse]

Hi,

I wondered what the forum thought of this noise coming from the right exhaust on my all original '55 Eldo?

It sounds like a misfire but I thought it may be a fuel issue. It's intermittent, sometimes it can go five minutes without it happening. It happens more warm then cold. It never happens on the left side.

I replaced the plugs, HT leads and coil and it's made no difference. The old plugs were a little black but not too much and all dry. The car is in all round good condition but has been standing for a long time and needs a proper run. The video was taken after a 20 minute run around the block several times. If anything I would say the car is a little low on power but I've got nothing to compare it against.

I'm in the UK and I'm running on high performance (over here it's 98 RON) ethanol free unleaded.

Any ideas what it might be or what I can check?

Thanks,

Andrew

[Cadillac Jack 82]

Timing or valve not fully closing/seating.

[Lockhouse]

Timing or valve not fully closing/seating.

Thanks for the reply.

Assuming the timing is OK, as the car has been sitting for a while is it likely that I've got a stuck valve?

If I have, will taking the car out for a proper run help free it up?

[klinebau]

The idle mixture might be a bit too lean causing intermittent misfires.  You might try enriching the idle mixture screws slightly to see if the issue goes away.  Keep track of the number of turns so that you can set it back if needed.

[Steve Lomas]

Andrew, I noticed the same thing in my '75 Eldorado a few weeks ago- getting progressively worse.

Similarly it was intermittent, happening more the hotter it gets. I also changed the plugs (wires are new) - altered the mixture screws- no difference there.

Then I noticed it smoothed out completely if I half closed the choke plate on the carb. So apparently it was not sucking enough gas- but idle mixture made no difference..

So I poured about half a can of Sea Foam down the carb and let it sit for about 20 mins. Then restarting the issue cleared up noticeably, still not perfect- so I'm guessing the carb just needs a good clean. May be something else entirely in your case but worth closing the choke as a test.

[Lockhouse]

Good suggestions re the choke and carb adjustment thanks. I'm driving to a car show tomorrow so assuming I make it there and back I'll have a much better idea of cause\effect.

[Steve Lomas]

Good suggestions re the choke and carb adjustment thanks. I'm driving to a car show tomorrow so assuming I make it there and back I'll have a much better idea of cause\effect.

Awesome, take some photos!

-is it just happening at idle? or with revs also?

[Lockhouse]

Awesome, take some photos!

If we make it I'll do my best!

-is it just happening at idle? or with revs also?

As far as I can tell just at idle but I'll know more after taking her on the motorway tomorrow.

Thanks

[Lockhouse]

Well she made it! There and back, nearly 100 miles including 90 minutes in stationary traffic. There's a little misfire and a lack of power going uphill over 50 (which I'll look at next week), but all things considered, the old girl done good.

[Steve Lomas]

Beautiful!!  Love the paint. Glad to hear she made the trip OK- and you got some roof-down weather.

If there's a little stumble on a long incline I'd maybe suspect the fuel filter to start with something simple, but plenty guys here who know a lot more about this era than I do.

[Caddy Wizard]

The misfire noise in the right exhaust could be ignition.  Probably not fuel, since it isn't happening on the left side.  Check to see if the plug wires are properly guided (held slightly apart from one another).  If wires are touching, you can get an induced back current in one wire from the current flowing in an adjacent wire.  So for example, when the spark is traveling down one wire toward the plug, it creates a magnetic field that induces a current to flow in the opposite direction in an adjacent wire if that wire is too close to the first wire.  This rearward flowing current can interfere with a spark that is trying to come down that second wire shortly after the first one fired.

Bottom line is that Cadillac used wire separators for a reason.  If yours are missing and the wires are just bunched together, you can get some funny misfires that are hard to track down...

[fishnjim]

What a good engine analyzer was for.  I don't go by sounds, could be anything from a bad muffler hanger to deep in the engine.
I'd tune it up first and see how it goes.  May just need exercised from sitting.
Can always pull that side valve cover and have a look see.