Engine breathers

[nickst4]

In light of Paul's comments on the effects the vacuum-balancing pipes can have, both on balancing and subsequent running, I'm intending to ditch them and plug the stubs, opening them only for carb syncing. There's quite a complex breather system on the Dart, and it occurs to me that the big green pipe wiv the baffles that the now-redundant vac-balancer tees into would then be surplus to requirements. Since there is a collector box for the breathers which presumably drains oil down into the cases again, I'm thinking of either venting the the box to atmosphere via the big-green-tube-stub or, preferably, into the airbox downstream of the paper filter so it doesn't get clogged. The latter option seems cleaner, so long as the rings in my motor aren't shot and the carbs fill with oil-mist! That way, breather emissions won't compromise the carb settings.

Anyone care to comment?

This w/e should see the re-float-valved carbs with all-new fuel hoses assembled, installed, and the whole thing come to life! It might be difficult to resist a quick run up and down the lane sans-bodywork if the weather is kind!

Nick

[morini_tom]

When I was running the 350 in my dart I junked the oil collector box and the green tube with one way valve.

I kept the carb float bowl breather pipes routed to the airbox to make sure the float bowls saw the same pressure, although I did move them downstream of the filter.

The stub on the carb outlet which as standard goes between both carbs with a t piece to the green tube I replaced with a single tube linking the two carbs.

The easiest thing to do with the crankcase breather is to vent it to atmosphere via a long large diameter pipe but don't forget to insert the plastic labyrinths to condense the mist. The dart as stock doesn't have these but they were fitted to the earlier 3 1/2s and I'm sure NLM can supply if nobody on the list can.

Rocker box breathers vent to atmosphere via long tube.

Also, modify the airbox as per the article in ATG a few months back.

I don't know if losing the emissions collectors gave any measurable benefit- I did it primarily to make space for an alarm where the oil collector was, but I don't see it doing any harm (other than to the trees) and its no different to the setup in earlier 3 1/2s then.

[nickst4]

Thanks Tom.

Running with the vac stubs blanked off completely caused massive overrun of engine speed with the throttles closed. Reinstating OEM didn't help much, but just connecting the vac-balance between the carbs is better, though the revs don't drop as I'd expect on any other bike. Is it to do with flat slides, which in turn need heavy springs? Having vac stubs integral with carbs is a new one on me, so there must have been a reason...

I did your air filter mod as my first job! At the moment, the Gazelle 'race' exhaust/open airbox seems to be causing lean running despite 115 mains, though raising the needles a notch has helped. Needs more though, I think, but this little motor flies!

As to breathers; Plan A at the moment is to run the big (green) collector-box pipe into the air box courtesy of 16mm silicone pipe, a copper plumbing elbow and a rubber grommet.

However, a more-important consideration is the crack in the fuel tank below the dread airbox-holding screw. As I see it, a separate support off the frame for the airbox will see all stress removed from the tank at that point, and permit some sort of sealed patch held on by the redundant screw, which may then have a better chance of holding fuel in. Unless the GFRP tanks mentioned in ATG are a realistic option, ethanol-containing-fuel notwithstanding.

Nick

[EVguru]

Running with the vac stubs blanked off completely caused massive overrun of engine speed with the throttles closed. Reinstating OEM didn't help much, but just connecting the vac-balance between the carbs is better, though the revs don't drop as I'd expect on any other bike. Is it to do with flat slides, which in turn need heavy springs? Having vac stubs integral with carbs is a new one on me, so there must have been a reason...

It's probably 'hanging' on the ignition advance which is quite abrupt on the Kokusan system. Retarding the static timing will stop that happening, but means you'll run a bit retarded at high rpm. There's a mod than can be done to the trigger block on the flywheel to reduce the advance at idle. http://morinist.dk/morini/lastrega94.php

However, a more-important consideration is the crack in the fuel tank below the dread airbox-holding screw. As I see it, a separate support off the frame for the airbox will see all stress removed from the tank at that point, and permit some sort of sealed patch held on by the redundant screw, which may then have a better chance of holding fuel in. Unless the GFRP tanks mentioned in ATG are a realistic option, ethanol-containing-fuel notwithstanding.

You can get ethanol resistant sealants for plastic/fibreglass tanks.

[nickst4]

[It's probably 'hanging' on the ignition advance which is quite abrupt on the Kokusan system. Retarding the static timing will stop that happening, but means you'll run a bit retarded at high rpm. There's a mod than can be done to the trigger block on the flywheel to reduce the advance at idle. http://morinist.dk/morini/lastrega94.php
.

Very interesting! If I understand the Google Danish-English translation, the effect is not to retard the top-end but advance the bottom end. Has anyone here done this? It looks beguilingly-easy. The writer suggests it's a very significant improvement to the bike's manners....

Nick

[mantaray]

I modified the flywheel last year, it's much better .
Removed 10mm

[nickst4]

I modified the flywheel last year, it's much better .
Removed 10mm

Hi Mantaray,

Thanks for coming in on the discussion.

If you have time, would you like to describe your experience a bit more, please? What did you see as the problem, and what exactly was the outcome? Did you need to make any more adjustments such as repositioning of the pickup, or carbs?

Nick the Newbie

[mantaray]

A little difficult to explain the situation but i 'll try

When i was driving my Dart and closed the gashandle, there was always a delay.
The engine revs stayed on 3000 rpm for 5 seconds or more before going to idle
Changing the ignitiontime didnt change anything.
It's a common Dartproblem.

Till someone from the German Dart drivers discovered that the strip on the flywheel was a little too long
If you cut 10 mm (like shown on the danisch site) the hanging issue is much better or even completly gone.

(Søren, i have stolen your picture )


I hope you understand my Belgian-English

Didnt touch the carbs or ignition after the mod.

[nickst4]

A little difficult to explain the situation but i 'll try

I hope you understand my Belgian-English

.

Perfectly, thanks. I can see that the author of the piece is analytical and thoughtful, so his cure is very credible, but I just feel better having 'spoken' to someone with direct experience! I shall definitely go ahead with the mod as my few minutes experience of the Dart exactly matches your description. I'd prefer to do it with the flywheel off the bike, not least because there's a fair bit of petrol vapour around at the moment and a spark from a grinding wheel might terminate the whole project! I've got a flywheel holder (the nut was worryingly-loose) but just need to get the proper puller from NLM....

I have a good feeling about this bike, and it certainly should ride better than it ever has before. A bit mad I'm afraid, but I even invested in a cheap alternative registration number just so I could legitimately get a much more compact number plate to match the scale of the machine!

Nick

[mantaray]

The author of the piece is owner of a few Dart's and has a wide technical background.
Special intrests Morini's and Motobi's and well known in the German Moriniscene.