The Morgan ran very well during the Marvelous May races at Eagles Canyon.
Well, for the most part, at any rate...
Those of you that wrench TR engines, please read and comment.
Occasionally, when applying throttle, the TR4 engine seemed to run on two
cylinders. It seemed to happen only after I had used more engine braking than
usual, such as when coming up behind a slower car when approaching a turn, yet
arriving too late to attempt a pass, initially never occurring when I was
running in the clear. Changing up or down a gear would not immediately fix
it. Pushing in the clutch and revving the engine up and down the rpm range
did not immediately fix it. If I held steady throttle and just waited about
7-8 very long seconds (while waving following cars around me), it would
eventually clear. I did not encounter a situation on the track where I was
willing to just try letting it idle to see if that would resolve it, and it
always cleared up before I left the track. The condition was either fully
present or fully absent.
I first thought that perhaps a plug change would fix it. The car has a
Pertronix distributor and all the parts visually appear to be in good
condition. Given that the engine runs strong and that no changes have been
made since it was tuned on a dynamometer I was surprised to find the plugs
somewhat dark. The car felt stronger with new plugs but the condition would
still occur with about the same frequency. I tried avoiding letting the
engine overrun and downshifted at the last second to draw less fuel into the
cylinders, and I also tried a bit of left foot braking at the end of short
straights, maintaining a bit of throttle while in gear. That worked pretty
well at first and the condition happened only once per race after that until
the final race on Sunday. Given all that I'd witnessed far, I reasoned that
it was most likely fuel system-related. The carb dashpots were empty of oil
(this didn't seem unreasonable, having recently read Kas' tuning books) and we
topped them off with 20 weight oil. I couldn't remember when the K&N air
filters had last been cleaned so we removed the air cleaners. No other
changes were made to tuning.
No dice. During the last race I couldn't string more than two corners together
without a return of the condition, so I left the race rather than be a mobile
chicane. I checked to see that the carb slides would drop easily on their own
and those seemed just fine.
What I witnessed seemed most consistently to follow engine braking. During
the last race it might happen if I lifted throttle briefly, say in the middle
of a twin-apex turn. I don't associate these conditions with ignition
problems since it ran strongly otherwise. I considered a loose ignition wire
shifting under deceleration as a possible cause, but this only seemed to
happen after allowing the engine to overrun and did not happen after hard
braking only.
One potential cause for a carb change is that I removed the carbs to add an
intake manifold brace, attempting to avoid changing any adjustments
whatsoever. However, the possibility that I might have inadvertently tweaked
the carb synchronization doesn't satisfactorily explain this condition for me.
It did not correlate to ambient temperature and the engine never ran hot.
I am wondering if a coil can give good enough spark to run the engine cleanly
and strongly when the throttle is wide open yet allow the plugs to load up at
smaller throttle settings. The car has a Bosch blue coil -- and... hmm! It's
still mounted on the side of the engine, which I realize can create conditions
for coil failure.
My plan of attack is to first look for debris in the fuel system, however I
don't expect to find anything, because if running it at full throttle in high
gear didn't precipitate the condition, blockage or restriction would seem
unlikely. If it relates to fuel sloshing forward under deceleration, I reason
that heavy braking would likely have caused the same situation. If I find
nothing there, my second plan is to check out the ignition system thoroughly
before attempting to make any changes to the carbs. The engine ran without
fault in February with the exact same carb settings.
Thoughts? Suggestions?
Duncan Charlton
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