I'm not a carb expert, so I seek the advice of those that are. I believe
one, if not both, carbs have developed flat spot.
My definition of a flat spot is that a certain angle rotation of the
throttle shaft, the gap between the body and throttle shaft is greater than
normal, causing additional air to enter, leaning the mixture, and thus a
loss of power. If that definition has a another name please let me know.
In my case, twin HS6's, when the engine speed gets above 3K, and the
accelerator is at a certain spot, the engine seems to act like fuel
starvation and have a loss of power. Pushing the accelerator beyond that
particular point causes full power. Letting off from that point causes a
"surge". In fact, a suction sound, like a whistle, can be heard while the
accelerator is at that certain point. This certain point of rotation is at
where I drive a lot at on the freeway
The carbs are kind of hard to tune at idle, and seem to adjust on the rich
side (about 3 1/2 turns). A Gunson shows a correct mixture. Lifting the
carb-adjust piston 1/16" shows a lean mixture.
Spraying carb cleaner around the throttle shafts at idle has no effect. As
does spraying around the manifolds, manifold gaskets or any carb. The spark
plugs are a light sand color (actually almost white on the piston side, and
sand colored on the valve side).
Stock cam. 87 MM pistons. Everything else stock. The carbs were rebuilt by
Joe Curto about 10K miles ago. I know Joe bench tests these rebuilds, but
testing under load is another thing.
Any insights, testing, or possible causes would be helpful.
Thanks!
John
'67 TR4A
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