Spark Plug Color

[RonR]

Folks,

After a 500 mile round trip a few weeks ago in my 1959 Austin-Healey 3000, I decided it was time for a tune up in preparation for my favorite driving season (30 to 40 degree top down winter driving).

I must confess that the car has not been tuned up for over 15,000 miles.

I have discovered a strange color to all six the spark plugs. It is a dark reddish brown; almost a rust color.

Any idea what this means as it relates to the air/fuel ratio?

I did discover that at least one of the gross jets for the float chamber was not closing (fuel pump would not stop clicking even at highway speeds).
I have installed new needle and seats, which appears to have solved that problem.

Thanks in advance.
Ron

 

[red57]

If you can post some pictures, it may help us. Particularly close ups of the porcelain and the electrode tips.

If they are all the same, it may simply be down to the brand of fuel you are running.

How does it run? Is the power down? Have you done a compression test?

 

[RonR]

My car needed some tune up work.
I replace the points and condenser, spark plugs, the needle and seat, and adjusted the floats height.
A new distributor cap and rotor are on the way from Toms Import Sales (Moss dealer).
The car runs great.

Attached is a picture of the new spark plugs, after a 30 minute drive. They are all the same color, leaning towards the red/rust color.

The compression is around 155 psi (dry) throughout.

The floats are still in need of fine toning, as I am getting fuel out of the manifold drains.

Thanks.
Ron

 

[red57]

Hi Ron, the picture is a bit blurry but if that represents 20 miles or so, it is way too rich - fresh plugs after 20 miles should still look like brand new plugs. If they are all the same color, that indicates both carbs are set too rich. I still have no guess as to what the reddish color means.

Last year I had one plug out of the six that showed some reddish color. Plug #3 in the pictures below - this was at about 6500 miles. Don't recognize the color as any particular warning so I'm still driving....

I am not a believer in gross jets and prefer stock viton-tipped needles. Your car should have a pair of HD6 carbs and the float valves should be set using a 7/16" test bar as shown in the manual - no fine tuning required. You can easily check that they are shutting off correctly by removing the dashpots and vacuum pistons and looking at the tops of the jets. With the pump on, the fuel should be just below the tops of the jets and none should be flowing out of the jet. If there is fuel flowing out of the top of the jet the needle valve is not shutting off correctly. Make sure this is correct before you try another test drive. Don't worry about whether the pump is ticking or not, they sometimes tick even when the flow is shut off due to internal.

Once you are sure the float needles are functioning correctly, you can proceed to adjust the carbs as outlined in your shop manual.

 

[NutmegCT]

I'm dense ... but what were the plug colors *before* you did that 500 mile trip?

Also, those red/orange tips look like extreme heat.

TM

 

[Michael Oritt]

What are using in the way of fuel and fuel additives, if any.

 

[RonR]

I will adjust the carbs next weekend, or one night this week, and report back.
I have an old Sun exhaust gas analyzer that I use to set the air/fuel ratio. Maybe it is no longer accurate.

I use premium, ethanal free, gas with a lead substitute/octane booster (Instead of Lead Gold, which is no longer available.) The engine was originally rebuilt in the early 1970s, with a 10:1 compression ratio. Then the car sat for decades before it was completed around 2004.

I did not check the plug color prior to the last 500 mile trip.
For the past 550 miles, the engine temperature has not gone above 170 degrees.

 

[Michael Oritt]

I will adjust the carbs next weekend, or one night this week, and report back.
I have an old Sun exhaust gas analyzer that I use to set the air/fuel ratio. Maybe it is no longer accurate.

I use premium, ethanal free, gas with a lead substitute/octane booster (Instead of Lead Gold, which is no longer available.) The engine was originally rebuilt in the early 1970s, with a 10:1 compression ratio. Then the car sat for decades before it was completed around 2004.

I did not check the plug color prior to the last 500 mile trip.
For the past 550 miles, the engine temperature has not gone above 170 degrees.

Ron--

I asked because supposedly the manganese in some lead substitutes can turn plugs red/brown. Perhaps you should check out the additive you are using or consider switching to pump premium and see what effect that produces.