Have also had similar problems with high speed miss a number of times as
engine development has edged forward over the years. I'm sure it's
caused by increasing fuel consumption.
Still running SU's thru this whole story by the way.
First it was as Jack has written, just not enough umph from the little
facet pump. Went to a carter rotary pump in the trunk next to the fuel
cell and a regulator under the hood near the engine. Grose jets in the
carbs worked well until the next little set of head work and then we
think the problem became not enough flow thru the jets. Now using a
viton needle setup in the carb bowl, it seems to easily hold back the 3
psi or so the regulator is set to. On rare occation they will get a
little junk stuck and not seal well but we are living with that
aggravation.
And our most recent problem seems to be not enough air flow. High speed
problems clear up if we take the air cleaner material out of the little
half dome shape cleaners we have. They look very period but I worry
about running with no aircleaners, particularly since we have rather
sandy soil here in Florida.
mike jackson
Jack W Drews wrote:
>
> Chip Bond and others having high speed power loss problems --
>
> Last year I chased this very problem for three races.
>
> I had one of those ice cube sized Facet pumps and a pressure regulator
> on it, regulated to three pounds. The engine cut out part way down the
> straights something awful.
>
> Ended up with the interrupter type Facet pump and no regulator and also
> no more problems, although pressure at the carbs was 5 psi, higher than
> I wanted, using Grose Jets with no problems from them. I purchased that
> pump only because it was available at the track. Ran the last three
> races with no more problems.
>
> This year we again have the same symptoms. Car loses power on the
> straights at Road America and when this happens, EGT goes up, indicating
> leaning out.
>
> We did some head work over the winter and I am theorizing that the flow
> increase is causing enough more fuel consumption that the pressure and
> flow at these high demands is not enough. This theory is based on
> measured mpg for a lap and flow / pressure measurements at the carbs. It
> may be a wrong theory since Triumphs don't respond to well to
> well-thought-out theories.
>
> Since I purchased another identical Facet pump trying to diagnose the
> problem, and I had two on my hands, I have installed them in parallel.
> My measurements of pressure vs. flow with both setups shows, not
> surprisingly, an increase in both. I will see if this fixed it at the
> next event. The guys who don't seem to have any of these problems have
> big Holley fuel pumps and healthy regulators.
>
> By the way, one lesson learned for sure in all of this is that these
> pressure regulators work consistently only when dropping the pressure
> significantly - they do not seem to work when set to drop 5 psi to 3
> psi, for example.
|