1. Idle Air Jet
Passageways
These get blocked off frequently by incorrect installation
of air cleaner gaskets and/or air cleaner bases. See
diagram in instructions. The problem was corrected in late 2002 by
manufacturing air cleaner bases which
only go on one way and air cleaner gaskets with extra holes. These item are
available from PMO.
2. Float Needle
Valves
We started out with viton float needle valves which have a
somewhat blunt viton tip. Historically, these have been the choice for off-road cars.We changed to the
Weber float needle valves when we found quality control problems with the viton valves. After that, we went to
the double-ball type. Both didn’t work as well as the viton ones for holding
fuel level. Consequently, we went back to viton, but we now individually
inspect every valve. As a footnote, not
even the viton valves will hold the fuel level in some cases where solid motor
and transmission mounts are used. For race cars, we recommend the clubsport
mounts which can be stiffened by modification. WEVO recently
developed urethane motor mounts which should be the best of both worlds.
3. Leaning Out
Cruise and Idle
For street cars, the idle and cruise conditions can be
leaned out if necessary by opening up the air screws to 1 or 2 turns initial
setting. This leans out idle and cruise by giving more air without more
throttle. Ideally, at idle, the cross
section of the throttle plate covers the first transition port and the engine
idles as sufficient speed with 6 to 8 degrees spark advance. Idle speed can be
adjusted with the air screws without disturbing the throttle settings.
4. Reducing
Injection Quantity
We have found that race engines often need varying levels of
injection quantity. Coming out of a turn, too much injection quantity can
actually cause bogging. PMO has different float bowl check valves to adjust the
injection quantity up or down. Rob King at S-Car-Go has cut the injection
quantity down to almost nothing with excellent results. The normally installed
float bowl check valves have a .5 mm side hole for bleed back. The larger the
bleed back hole the less injection quantity. The valves come in increments of
.1 mm up to 1 mm. We have 1.5 mm valves for people who want to almost eliminate
injection quantity but still start the engine.
5. More on Idle
Air Jets.
We made these out of brass for the most part. In humid
climates they tend to corrode because of the interaction of the brass, the
aluminum throttle body and the vegetable material top cover gaskets. We’re
changing to stainless steel on the idle air jets and looking for a durable
paper for the top cover gaskets. If you have a problem with corrosion on the
brass idle air jets, this can be removed by soaking in vinegar. Spray the top
cover gaskets with WD40 before putting top covers back on, or check with us
about stainless steel idle air jets. We should have the new top cover gaskets
by March, 2003.
6. Solid Motor and
Transmission Mounts.
I've noticed a proliferation of advertisements for solid
motor-transmission mounts for
Porsche 911 race
cars. I'm sure they sell well because they are CNC machined out of solid
aluminum and they look "cool". They are also considered
"hardcore". My opinion is that any practical advantage they possess
is vastly outweighed by a myriad of disadvantages.
The basic problem with solid mounts in internal combustion
reciprocating engines is that they introduce destructive harmonics into the
body of the race car and also back into the engine. Everyone has heard the true
stories of cracked sheet metal, loosened nuts and bolts, sheared-off exhaust
systems and broken engine cases.
The excessive vibration often sticks the float needle valves
in carburetors causing flooding and other times aerates the fuel in the float
bowls causing a lean condition.
The intense vibration also can knock out components in EFI
systems leading to the common full-lean-at-full-tilt-equals-fried-engine
syndrome. The additional tooth- rattling vibration and noise increases driver
fatigue and the possibility of a crash. And if there is a hard crash, the solid
mounts increase the likelihood of catastrophic damage to the engine and
transmission.
Given these well known facts, why would anyone use solid
mounts? It is because they stop the engine-transaxle unit from twisting,
thereby improving shifting. This condition is substantially improved by using
the Porsche sport mounts and is totally cured by using a WEVO shifter
along with the sport mounts. Frank Eibell in