adaptor made using threads from 10mm plug.
Plug with adaptor on engine.
The new adaptor
was made using the threaded portion of one of the 10mm long reach
plugs. The 14mm female thread in the adaptor was made the hard
way using a 14mm thread chaser which wasn't designed for threading.
It took a while and a bit of elbow grease but it did make
good threads. The adaptor has a little more volume than the short
one and allows more thread engagement in the head and full engagement
for the plug.
The engine started readily and ran pretty well
but, not being satisfied, I stopped it and removed the 14mm plug and
used the sleeve that I made yesterday to give more volume in the
adaptor. This time, the engine didn't run as well. I think
the problem is that I finally got enough volume between the plug and
the combustion chamber to make the charge at the plug iffy. The
engine would accelerate fine but when it was allowed to idle, it
8-cycled no matter how the fuel mixture was set. I think that,
with the denser charge on acceleration, enough mixture got to the plug
so it could ignite it more reliably but was too rarified at low
throttle settings. I went back to the new adaptor and the engine
ran a lot better.
Then, while I was sitting "supervision", it
began to occasionally run rough, hunting and misfiring. It would
eventually correct itself. The engine skid was sitting on
concrete and I could see it teetering a little. The teetering got
worse when the engine started acting up so, on a whim, I put my foot on
the skid to hold it steady. The engine straightened out and ran
right. I figured (correctly) that the problem was a bouncing
The check valve was removed and the 0.130" ball was
replaced with a 0.200" ball (the biggest that would fit in the
housing). After that, everything was hunky-dory. I refilled
the gas tank and ran it dry, having to occasionally open the needle
valve as the fuel level fell. Just before it ran out of gas, the
temperature was just barely 250F
I tweaked on it until it would
run well at 400 RPM if I kept an eye on it. If I revved it up to
around 1,000 RPM and advanced the timing, it ran really well but I
don't want to run it that fast. I set the speed to between 450
and 500 RPM for the run,
I've got to see what the ignition
timing is when it's running around 500 RPM. I think it is firing
after TDC for best running.
8 May 2017:
I made a new needle valve assembly. The needle has an 8 degree
taper and seats against a #65 (0.035") jet. This gives a much
When tested on the engine, it worked a
lot better than the larger one and the engine is nearly ready for prime
time. After running a full tank of gasoline through it at between
400 and 500 RPM with the timing retarded so it ran well, the
temperature was just a slight amount above 250F. I think if I can
get a handle on the timing issue and get it running with spark advanced
a few degrees, it should run substantially cooler.
400 RPM, in order to keep it from 8-cycling, I have to run the spark
timing retarded 30 degrees after top dead center. I don't know
where this oddball timing is coming from. Too little flywheel
mass? To high compression? Even at 700 RPM the timing is
running about ten degrees retarded. This is a mystery to me.
Anyone got answers?