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A
heated air fuel meter will be able to read accurately down to low power
settings. A two wire, not so much. It goes in the down pipe after the
collector and gives an average reading for all housings. This is what
you look at for mixture readings below wide open throttle cruise RPM
mixtures.
For EGT readings (Exhaust Gas Temperatures) install a probe in each of
the three pipes 3 to 4 inches out from the flange face (all the same
distance). They will not fit gas tight, but pressure this close to the
engine is below ambient, so a bit of air will leak into the exhaust
flow if a leak is present. The EGT gage gives you a good picture of
mixture ratio at full and near full throttle. At lower throttle
settings EGT is worthless.
Add fuel until the max EGT is 1600 degrees or less, say 1550 to 1600.
Just a hair rich of best power. Makes apex seals last a long long time.
This will be in the 12s on the air/fuel gage.
Looking at plug color in this age of unleaded fuel is of no value.
Racers used to do a clean cut going into the pits so the engine man
could read the plugs. Looking for light gray color on the intake valve
side of the porcelain. Yes we indexed plugs with a mark to show where
the ground electrode was, and installed plugs that would have the
ground away from the intake valve when installed at rated torque. In
any case, a clean cut was at full throttle at peak power rpm. As you
slow and turn in for the pits, you downshift and squeeze on the brakes
and throttle to hold max power for a half second and cut the ignition.
Slip into neutral. For lower powered cars this is no problem because
they cannot spin the tires. Not possible on bigger engines, but you can
do it on the straight and cut and coast into the pits.
The object is that the engine man wants to see the plugs as they
appeared at the power peak and full throttle. The EGT gage and fuel air
gage did away with the clean cut, and even reading the plugs.
The plug color he was looking for was from lead salts on the porcelain,
and with unleaded fuel there is just a black color no matter the actual
condition of the burn.
If it gets to 4,000 RPM and stops one or more housings are out of fuel. This is with a prop installed?
The unequal length header pipes make each housing happy at a different
RPM. So you have three engines on one crank. This might help spread the
power band a bit but reduces peak power. You always end up with one
housing doing a bit better than another and that has one or two
housings pulling on the third. This will show up as an imbalance
(vibration) that changes RPM with tuning changes.
Most typical is lack of fuel. Lack of fuel pressure. Use a Carter
sliding vane 7 PSI street racer pump and start at 3 1/2 pounds of
pressure.
It must hold that pressure at full throttle, peak power RPM. If you
like the Facet you can put two in series to get more pressure.
If there is a filter under a brass plug at the fuel inlet, discard this filter. Use an in-line filter close to the carb.
Lynn E. Hanover
I have just started running my engine on a test
stand. currently it will only do 4000 rpm. I noticed the rear rotor
exhaust has turned blue. I pulled the plugs and the rear lead and trail
plugs were very sooty. the front rotor trailing plug was clean, lead was
black. I suspect that my trailing ignition for the front plug may not be
running correctly. getting started I have been running whatever jets that
came with the carb. it appears I need to change them, to smaller I
assume. do I need to install a mixture gauge? does it attach to the
exhaust or intake? if so, which pipe(s)? |
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