Intake
The Dart was
built to meet emission standards in force in some contries and the
performance suffered as a result. The air filter assembly is the
bigest culprit. The Dart uses a 92 main jet in comparison to the
Strada with 112 and the Sport with 115. Since the Dart cam is about
half way between Sport and Strada profiles it's either running very
lean, or the air flow is so restricted that a 92 jet gives the
correct mixture.
This is
actually an Excalibur 350 airbox, but it's the same as the one on a Dart.
The contents
of the airbox revealed. Top centre is the sleeve that fits over the
filter element (below).
This 'Flower
Pot' is the cause of nearly all the restriction, so much so that
leaving it out results in an unridable bike unless the jetting is
altered to suit. I used a pair of 112 jets, but others have gone as
rich as 118. A dyno run would be the only way to know for sure.
There are two
filter element supports. This is the one on the left in the picture
above. How much it actually effects the airflow is unknown, but it
protrudes into the filter quite a way and can safely be cut back to
just beyond the tapered section and given a generous radius.
The last
intake modification is to get rid of the crankcase breather valve.
There is a balance pipe between the two carburettors and the breather
valve runs off a tee piece in this pipe. The valve tends to get lazy
with age and opens too easily, causing an erratic mixture. It can
also cause the revs to 'hang' which is very anoying and makes riding
in traffic a real pain. Simply replace the balace pipe with a single
piece of tubing and leave the valve out. I hadn't taken enough notice
of fuel consumption to tell, but another long term Dart owner
reported a useful decrease in fuel consumption when he also removed
the valve.
Exhaust
The exhaust
system is also quite restrictive. The first restrictive item is the
collector box. This item is very prone to rotting out ond originals
have not been available for many years. Many people replace the
collector box with a 'Y' piece. I was in a hurry and didn't have
suitable tubing around, so I made a new collector box out of sheet.
Needless to say, this lacks all the restrictive baffles of the original.
I also needed
to replace the silencer, which had completely fallen apart when I
took the system off to replace the collector. There are many modern
OEM or aftermarket silencers that can be pressed into service, but
again I was in a hurry, so made one up.
Despite being
a straight through design it's remarkably civilised, I think this is
down to having used a collector box, rather than a 'Y' piece.
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