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1955 Cadillac 331 spark plug problem HELP!!

Started by Jason L, June 10, 2005, 09:33:45 AM

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Jason L

Can someone please help me, i have 2 cadillacs with the same problem.
A 1955 Eldorado and a 1955 limo.
The plugs only last for a few weeks they get a black type carbon on them and the car starts to run very ruff, in the manual it says to put 43-5 type plug in the Eldorado.
On the limo it says to use a 44-5 plug.
Im located in Australia and i am finding it hard to find those plugs, they do not use these ref. numbers anymore, the equivalent is ngk bp4, but they are not lasting, i think they are the wrong plugs.
The cars have original equipment, but the Eldorado has an electronic ignition kit installed that is the only mod. on the cars.
Can someone suggest the correct plug i could use, the cars have had compression tests and are good, carbis have been rebuilt.
Thanks....
Jason.......

Paul VW

The black type carbon seems to indicate a very rich fuel mixture, which would cause the plugs to foul.  If you can ge ahold of a Gunsons Color tune kit (which is a sparkplug with a see-through top) its an easy and sure way to see (by flame color) if the mixture is too rich.

Bruce Reynolds # 18992

Gday Jason,

Firstly, are you running LRP or Unleaded?

If you are running LRP, then change immediately to Premium ULP, or normal ULP if your compression ratio is less than 9.5 to 1.

Dont forget that without a Cat. using ULP will produce more volatile Pollutants than Super, so dont get anywhere near the tailpipe.   Not good for ones health.

If the answer is LRP, then I wouldnt be surprised if the problem lies there, and if you are running any sort of petrol diluted with Ethanol, then go to the pure stuff.

I also agree that the engines are running rich, but the plugs shouldnt carbon up that much.

The days of reading the plugs as per using Super Petrol, (Leaded), that is a nice grey colour, are long gone, as these days, everything is black.

With the Eldo with thew electronic Ignition, check with the instructions that came with the kit, as I wouldnt be surprised if it recommends that the gaps be widened.   Normally, the reading should be .034, but I have known electronic ignitions to require gaps up to .060.

Bruce,
The Tassie Devil(le),
60 CDV - rund Premium ULP with a Fuel Cat.

Jason L

Hi Bruce
Im using premium unleaded 98 octane, the gaps are 0.28,
also i put in a lead fuel aditive from time to time.
Jason.

Bruce Reynolds # 18992

Jason,

Okay, then increase your spark plug gaps to .035.   .028 is too small and this allows a small spark and promotes carbonning up.

Also, make sure the dwell is within specifications with the engine with the Points.

Bruce,
The Tassie Devil(le),
60 CDV

Jason L

Hi Bruce the gap on the Eldo is 0.32 my mech. told me.
do you think the carbis might have something to do with my prob? The car comes from Canada. With the altitude diff. and climate, do you think this could also be one of my probs?
Jason........

Bruce Reynolds # 18992

Jason,

The Altitude in Canada is the the same as anywhere else in the world.   Water Level is Water Level, where ever one goes, but granted, Canada does have a couple of mountains that are taller than ours.   And, when it is hot in Canada, it is just as hot as it gets here, but, yes, it does get a tad colder.

The only difference between the two hemispheres is the way the water goes down the plug-hole.

But, If your carbies are running richer jets, then the engine will foul-up, but the mixture screws will stop that at idle and off idle.

I would be checking the float levels, and making sure that you have the correct jets installed for the altitude where you are.   Wouldnt have a clue as to what they are meant to be, but John Washburn in Colorado would know.

I still say .035 on the Plug Gap.   I dont know what book the mechanic is reading, but dont close the gaps up too much.

Bruce,
The Tassie Devil(le),
60 CDV

John Washburn

Hello,

Altitude and jets need to be close so that things work well.

Give me a hint about the altitude and the jets sizes and we might be able to see if you have a problem or not.

Sea level to a couple of thousand feet is not big deal, it is when we start to get above this that jets and metering rods need to be looked at.

Oh, what type carburetors do you have? Rochester or Carter?

John Washburn
CLC #1067

Elizabeth, Colorado = 6500 feet

Come see us...

Jason L

Hi we are at sea level it is a 55 eldorado with 2 rechester carbis , i am using electronic ignition with NGK BP4 plugs set at .032.
I keep fowling plugs at the front,not sure  on jet sizes.
The car originally came from Toronto Canada.
Jason...................

Bruce Reynolds # 18992

Jason,

Sounds to me like the front carby is running way, way, way to rich.

And, I still say run the gap at .035.

Bruce,
The Tassie Devil(le),
60 CDV