January 28, 2020

Looking for a Well-tuned Mind

Illustration by George Danby

Illustration by George Danby

• By John F. Chisholm •

When I was a kid in school I didn’t do badly on reading comprehension tests.  Mind you, I’m not a Rhodes Scholar.  I got by.  But the importance of understanding what you read never dawned on me so forcefully as yesterday.

I’ve been having terrible troubles with the Daimler fouling sparkplugs.  I tore my hair out over it ― figuratively speaking.  I cleaned and changed those plugs dozens of times.  I switched them over to ever hotter varieties, trying in vain to burn them free of carbon.  No matter how carefully I timed the engine, how painstakingly I adjusted the carburetors, that dreadful carbon coating always reappeared ― and in very short order, too.

Finally, in desperation, I located and ordered an out-of-print publication, “Tuning S.U. Carburetters.”  From the spelling of ‘carburetors,’ you can tell it’s a British book.  That’s OK.   The Daimler is a British car.  Who better to help me with this problem?

The book arrived.  I dutifully read it.  It’s quite short, only 128 pages.  Shortening it still further, there are elaborate appendixes at the back that take up a great deal of text.   I scanned them.  Then I put the book on the shelf and went back to cleaning sparkplugs, fiddling with the carburetor adjustment screws and swearing.  Yeah.  I did lots and lots of swearing.

At last, completely stymied, I removed both carburetors, pulled out that book again and sat down to understand it with the offending pieces right on my lap beside it.  I slogged through the book, point by point, page by page, determined to find the answer.  Finally a paragraph on the bottom of page 29 leapt off the paper.  If only it had grabbed me by the throat the first time.  I re-read it before re-reading it again, before underlining the following quote:  “The actual setting  of an SU on a tuned engine follows exactly the same procedures as has just been outlined, but with one very important exception.  We cannot assume that the [carburetor jet] needle is correct for the particular state of tune of the engine.”

The light, so long in coming, illuminated at last.  Looking back through the text, I discovered numerous other references to this very issue.  For example, “It needs only minor modifications to the engine to warrant a different needle.”  My engine is certainly modified. It’s completely rebuilt.  I rolled my eyes toward the garage ceiling.  How did I miss this?  Then I read on.  “Carefully select the proper needle from the charts at the back of this book.”  And etcetera.

How many times, in how many variations had I read exactly this thought and blown right by it?

Obviously, it takes a lot to get through to some people.  Me, for instance.
Going to the workbench, I assembled the necessary tools.  Then I removed both needles from those carburetors.  Grabbing a caliper, I compared each to the figures given at the back of the book.  It must be noted that the measurements given are extremely exacting.  In fact, the specifications are listed to the thousandth of an inch.  Some measurements are even provided to the ten-thousandth of an inch.  I had to ignore any figures that far to the right of the decimal.  I haven’t the instruments required to measure anything so accurately.

But it didn’t take more accuracy than I own to see that both of my needles were way out of spec.  That’s because they weren’t even close.

Still, I saved those two needles in the event that I had to put them back in the car, regardless.  Then I located some brass stock to mount in my lathe in their stead.  The set-up took some finagling, the needles being quite small ― each only a little over 2 inches long and, at the base, just 1/8th of an inch thick.  The biggest problem was precisely centering the work.  (My lathe is geared toward much larger stock.  I didn’t  need that six-foot bed for this job.  My 14-inch chuck was of no use.  In the end, I had to mount a chuck within a chuck to neck down to the proper size range.)  Then I turned the brass down until the pieces met the chart specifications.

It took far longer to do than write about.  In fact, it took all day.  Remember, I had to make two.  (As it turned out, I made three.  The first was a dismal failure.  But it showed me what not to do.)

Finished at last, I installed the new needles, shortened the dashpot springs to the length recommended by the book and remounted the carburetors.

It was evening by the time I finally went for a ride.


At last I have a car.  Being tired and dirty couldn’t wipe the smile from my face.

I checked the sparkplugs again this morning.  For the first time, they were still clean following use.

That means I’m still smiling.

But my victory is tempered by a huge dose of humility.  Being blunt, it’s crystal clear that I could have had a car a lot earlier if I’d ever truly mastered that simple grammar school skill:  Reading comprehension.