hanging revs (SOLVED)

[mantaray]

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

When i am driving my Dart and close the gashandle, theres always a 3-5 seconds delay.
The engine hangs on 3000 rpm.
Then the revs are coming down and the engine is dying (if i dont play with the gashandle)

Before i bought the second Dart i had the 2 balance tubes connected to each other.
The " new" bike has a T pipe with a bigger tube (looks like a cranckcase breather from older morini's) leading to the box behind the engine .
I have mounted this bigger tube on my first Dart but it 's getting even worse.

Can i plug the balancetubes (without making a bridge between the carbs) ?

Found some details on Paul's Morini site, but without the "breather tube" the Dart still likes to "hang"

[morini_tom]

Yeah this is quite common with darts (not so much the dying engine but certainly the rev hangup)- and is truly frustrating at times. I find if you drag the clutch a little to bring the revs down then they usually stay down, but that's a nasty workaround, and doesn't help with coasting into corners on a fast idle or mashing the bike through the gears.

I've never found a definitive cause but I suspect something to do with the kokusan ignition not retarding sufficiently at idle and causing the revs to hang. (I don't think it's anything to do with the breathers)

Regarding the breather system- the big tube you describe is part of the breather system. There should be a one way valve in that tube which allows blowby from the crankcase and rocker box covers (these should be connected to the black box behind the engine) to be re-combusted. There are also 4 tubes which come from the float bowl vents on the carbs and go into the airbox intake. Check the one way valve is functioning correctly!

You have a couple of options with the breathers- vent everything to atmosphere as per early morinis (don't forget to add a labrynth to the crankcase breather) or leave it as is. I don't know if there are any measureable benefits either way (other than evaporative emissions). I junked mine when I installed the 501 for packaging reasons. If everything is connected and functioning properly on your bike I would leave the breather system as it is (think of the trees!) -Although de-restricting the airbox is worthwhile (has previously been talked about on the forum and I think on Pauls website)

Anyone else had this problem? (and sorted it out!) My guess would be that someone has adjusted the carbs to try and bring the revs down but that when the revs do drop the engine can't then sustain an idle. I would try retarding the ignition by moving the pickups a fraction (although you then retard across the rev range) and then re balance the carbs.

Let us know how you get on...


Tom

[mantaray]

One more remark: i used the bike in may for the last time (dutch morini club 25 years) and everthing was ok (except a little delay on 3000, but the engine didnt stop)
Here with a visitor from the UK


What i did today:

Tested with the carbs and the balancetubes : hanging at 3000 rpm for 4-6 seconds and dying (if i try to increase the the rpm at the carb(1/4 -1/2 turn)- the revs are going up to 6000 and very very slowly coming down till 1200- impossible to drive
Tested with balancetubes only :hanging at 3000 rpm for 2-3 seconds and dying.((if i try to increase the the rpm at the carb- the revs are hanging 6-8 seconds)

Raised the petroltank a little to look if there was some air in the tubes.
Then i got an overflow of the right carb---Strange-- (not the first time,had it in may after filling the tank)

Then i decided to take the carbs of the "new" Dart --- seemed a little bit better hanging 3-4 seconds and then 1000 rpm , most off the time it keeps running -- but i could not increase to 1200
Around 6000rpm in second gear it seems like it didnt got enough petrol (or to much ?), was shaking and needed several seconds to get to 8000-NOT GOOD

Oh yes , i attached vacummeters and both carbs are syncronised

So far for the carbs
Tomorrow i'll mount the originals again (i have checked the Float assembly and could not find anything special, blowing in the petroltube and moved the float up - then it was closed.)
They looked like new inside and there is a 107 main jet
Renewed 1 o-ring on the choke (little bit damaged)
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On my first bike there is a tiny hole (1mm) in the rubbers on the airfilterside.Why ? No idea
Today i tested with the new ones




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About the ignition.
I have 2 marks on the flywheel 50 and 35.(50 is 5mm more to the left)
Checked with a strob and the 50 mark was inline with the centre off the cam-shaft

Changed it to the 35 mark- no change in behaviour off the bike.
Not sure what the right position is for a 400 engine- the 35 or the 50.
What i noticed ,i from 3000 up, there is only a very little change in timing.



Selling new bikes with this behaviour is a crime - GRRRR Cagiva

[morini_tom]

To be fair to morini & cagiva not all darts do this so it's more setup related than a fundamental design flaw.

Regarding the ignition timing, on both 350 and 400 dart the 35 mark is correct (50 is for the 501 engines which use the kokusan ignition)

there are 2 ways to check the timing:

Statically:
turn the flywheel until the 35 mark lines up with the cam centreline. The rearmost pickup leadinge edge should be lined up with the leading edge of the raised trigger on the flywheel. If it's not then the pickup mounting plate can be rotated to make it line up properly (but you have to unbolt the flywheel for this as the bolts are underneath it)

Dynamically:

This is checked with a strobe on cylinder 1 at 7000rpm. The 35 mark should line up with thecamshaft centreline. Adjustment if it's not is as above.

[mantaray]

Ok the ignition is on the 35 mark (did it yesterday with the stroboscoop)

Today i refitted the original carbs with the rubbers from the other dart (the rubbers from my original showed a tiny hole on both sides)


Contact on--- and overflow.
Checked the floater and needle -- nothing special.
Refitted- leaking again.
Took floater from another carb and a new needle, ok now

Checked all the tubes and connected only the balancetubes NOT the breather .
Set the carbs to 1mm open .
Cut a piece off the left filter element support (like written on Pauls site)
Started and was running ok ,not hanging at all but if i closed the gashandle the engine died.
Turned the screw 1/4 in and the engine kept running, but now the hanging revs are back but only for a short moment.(1-2 seconds)
And no more problems at 6000 rpm

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The bikes are practical indentical , both 400's and both with airfilter.
My original has 107 jets and the otherone is running on 90 jets (maybe thats the reason why my original didnt run well at 6000rpm with the carbs and 90 jets)

[morinipete]

I know this might be after the event, but I remember the late Phil Smith telling me he had problems with the 'new' type ignition systems, as when trying to set the tickover you were also often in the rev zone where ignition advance was just starting, causing only tiny carb adjustments to create massive rev variations (on earlier systems the advance obviously takes place later/higher ?). As I say probably not entirely related, but perhaps some one could say exactly at what revs the advance curve cuts in, or whether there are any nasty 'steps' in the curve, as surges or rapid drops could be accounted for revs huntimng around such a specific step in the advance curve ?

Again perhaps not related, but on my old british bikes carbs often stuck open, not just due to wear, but due to both vibration and vacuums holding the slides open (the more widely open the throttle the more likely it is to happen). The same happened habitually on big Dukes. Answer, before trying anything else to address revs failing to fall, tension the slide return springs (with big washers, bits of cardboard, anything) to see if this improves things. If the slides are definately 'snapping' shut when you close the throttle and you still have hanging revs you have an arileak problem or 'hunting' ignition timing. If it's an airleak it should be popping or banging somewhere in the rev range, so if not it's ignition.

My 3 halfpence.......
Pete

[mantaray]

Hi Pete, the advance on de Dart with Kokusan ignition starts @ 3000 rpm --- the same the point where the system is hanging.

causing only tiny carb adjustments to create massive rev variations

That's a fact and with the breather attached even more (on my bike)

A friend in Germany (owner of several Darts) also pointed to the kokusan ignition

The slides?
I guess they are ok, because older morinis have the same slides without any problems.
Without running engine you can hear them closing if you let de gashandle go (big noise)

But what about the other morinis with kokusan or the 350's ?
Do they have the same problems ?

[EVguru]

In my experience it's caused by a combination of the sharp advance step, static timing and the breather valve sticking.

Early Morini twins didn't run a balance pipe between the carbs and I think that's the best setup although it's much more fussy about synchronising the idle stops and throttle cables if you want a flawless progression from idle. Simply replacing the T with a straight joiner, or replaceing the whole pipe between the carbs is the first step. The late Ken Philp reported a return to 75mpg after removing the breather valve after I discussed it with him. Modern fuel seems to have a faster burn rate which reduces the amount of advance needed, so the factory timing marks aren't necessarily correct. Retarding the ignition until the revs no longer hang (with the engine fully up to temperature) doesn't seem to have any negative effects.

[mantaray]

Thanks Paul, i have only the balancepipes connected.
Managed to let the engine run at 1200rpm without the 3000 hang.
see you tube
http://www.youtube.com/watch?v=q5aSGS4mqmM
After a while closing the gas resulted in killing the engine again. grrr

a ver y little change ant the screws and now it hangs sometimes on 2500 and drop till 1500.
that's the best i can get
It's a Pita when i deconnected the vacummeters and mounted the balancepipes the bike reacted not the same anymore

[mantaray]

and what about this ?
http://www.elektronik-sachse.de/index_en.htm

[EVguru]

It's a Pita when i deconnected the vacummeters and mounted the balancepipes the bike reacted not the same anymore

Balance pipe, singular?

The rise in revs after fitting the balance pipe is the reason I don't like it. It's letting in extra air from the opposite carb and raising the idle.

I did keep the carb balance pipe on my Darts, but I never got them anywhere as tractable coming off idle compared to my '77 Sport. The MOST important thing to balance is the throttle cables, then the idle stops. The throttle cable splitter on the Dart does make things rather eratic and I think NLM have a better replacement. I used Freccia ones which seemed to be much better made despite the shared Cagiva origin.

What size idle jets do you have fitted and what weight is marked on the floats?

[mantaray]

[quote="EVguru"
What size idle jets do you have fitted and what weight is marked on the floats?[/quote]

i think they are 50 , but not shure
i'll see tomorrow



Btw yesterday we did 200 miles and everything ok

[mantaray]

A sollution for this problem can be found here
viewtopic.php?f=16&t=2285