Moto Morini

 

 

 

 

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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