Hello everyone,
On this particular Spitfire it idles fine on the "stock needles". Bring the
engine RPM up to 3500 to 4500 RPM and the engine just falls flat like it was
starving for gas on stock needles.
Spraying "Chem-tool" in the throat of the carbs the engine RPM picks up
immediately confirming a "fuel starvation" issue.
Fuel Pressure and delivery is adequate. Fuel quality is good "not stale gas"
(this car had sat for a long time). Fuel tank, has been cleaned fuel filter is
new, fuel lines are clear, fuel pump is OK.
We did find the feed tube from one of the float bowls to the jet tube was
"kinked" after removing the protective spring around the float bowl to jet,
(that would certainly have caused a restriction that would have caused fuel
starvation). Replace jet/tube to float bowl.
Blocked off PCV valve and used a Vacutech smoke machine (basically applies
smoke to the engine, a leak in a manifold gasket or throttle shaft shows up as
smoke leaking out the origin of what would be a vacuum leak, wonderful tool
for looking for vacuum leaks on modern cars).Also tried propane and Chemtool
with the engine running to verify integrity of intake manifold gasket, PCV
valve.
Ignition system is perfect. Ignition coil has great KV output, scope pattern
great on an old Sun machine.
Compression, cylinder leakage all OK.
Even dropped exhaust at the header output thinking what if exhaust was
restricted.
We had even put a vacuum gauge on the intake manifold to see if back pressure
in the exhaust was effecting cylinder filling efficiency as engine RPM
increased.
Ignition total advance is about 36 degrees. Camshaft lift is uniform, (no bad
lobes)!!!
Our conclusion is it has to be the mixture needles as it runs great on rich
needles.
Any suggestions appreciated.
thanks
Pat Mannion
The Engine Room
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