I see symptoms like what you describe on many governed engines.
The cause is usually an excessively lean fuel mixture.
>>> Richard Gosling <richard.gosling@exprogroup.com> 09/27 8:38 AM >>>
Daffy seems to have an occasional poor running problem.
Most of the time she runs fine, plenty power (for a Spit), smooth (well, as
good as you expect for a Spit), no complaints. The problem occurred
yesterday while driving through stop-go traffic, and was apparent when
pulling away from a standstill. The problem continued until I had been
driving more normally on open road for a few minutes. I also had something
similar on the long drive up to Scotland, I was cruising along happily at
around 70 mph on the motorway, the problem occurred if I tried to accelerate
at all. I stopped to tinker for 15 minutes and when I started again (having
not adjusted anything but taken a couple of things out and put them back) it
was fine, but the problem returned later in the motorway journey. Once off
the motorway and on interesting country roads, accelerating and braking
between 40-70 mph and driving enthusiastically, she was fine.
The symptom is that, when I accelerate (even a little), the engine seems to
miss as often as it fires, so I get a jerk of acceleration, then the engine
misses and the car pitches forward, then fires, and thus I kangaroo down the
road in an undiginified manner, not gaining much speed, until I have enough
speed that I can stop accelerating and let off the throttle, then she will
cruise at constant speed with no real problem, until I need to accelerate
again.
I don't think it is purely an over-heating problem, as she was slightly, but
not exessively warm, and has run smoothly in the past while running hotter
(during the hot summer weather). However, it may be some problem that only
has an effect when the engine bay is warmer than usual. During most of my
driving she runs as well as she ever has.
For info, Daffy is a standard UK 1500 (apart from foam air filters), twin SU
carbs, standard exhaust, standard points ignition. Ignition recently
checked and spark is at 10 BTDC dynamic @800 rpm (as it should be), spark
plugs have biscuity-coloured deposits indicating the mixture, at least most
of the time, can't be that far off.
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