Its a mystery

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Ted.3593
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Joined: 01 May 2019 22:13
Location: Chesterfield

Its a mystery

Post by Ted.3593 »

Bear with me I'll get to the point.It started with quick fettling of the carbs being needed due to poor running when pulling away on myX3 Kanguro. A thorough clean of the carbs carried out and all rubbers and seals are in good condition,slides are correct way round. But when started up she is reluctant to run on the front cylinder, though sometimes helped by blipping the choke leaver. Cleaned agained in the ultra sonic bath blown through with air line. Same result .Swopped each carb over to the other cylinder. No better. Check valve clearances. Fine. Swap tranducers and spark plugs between cylinders No improvement.Found poorly fitted diode in the transponders supply wiring thought UREKA but no wrong again. Check compression, was pleased to see 190lb.But with the motor running at around 2000 revs although the vacuem gauge is seen to flutter in sync with the motor its stays around zero whilst the other cylinder climbs with revs from its starting point of 100mm at 2000 revs.I've the choice of connecting gauge to either the carb or inlet manifold both are clear and give the same result.
So the question is what the hell is going on ? How can the vac be so low with such good compression ? (Yes I've tried it without the air box.) Surely this has got to relate to the poor running on pulling away. Ironically she starts on the button.
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72degrees
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Re: Its a mystery

Post by 72degrees »

A foreign body stuck in the inlet port between carb and inlet valve?
Totally blocked exhaust header pipe?

My first thought was a duff ignition pickup but you appear to have eliminated that.

Did you swap the carbs and cables, or just carbs? Certain the front throttle cable is OK at the twistgrip end? Presumably you can see the slide lifting?
Ted.3593
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Re: Its a mystery

Post by Ted.3593 »

NO foreign bodies in the inlet and the exhaust is clear.Slide has been checked and moves in time with its partner.
Must admit having had a nice fat spark I've not inspected the actual pickup got be worth a look for damage, although still baffled with the vacuum.
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72degrees
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Re: Its a mystery

Post by 72degrees »

Ted.3593 wrote: 07 Feb 2022 16:37 NO foreign bodies in the inlet and the exhaust is clear.Slide has been checked and moves in time with its partner.
Must admit having had a nice fat spark I've not inspected the actual pickup got be worth a look for damage, although still baffled with the vacuum.
Not always easy to spot damage. Substitution with a known good one is the sure diagnostic. Or you could swap the sender leads between transducers and HT leads between plugs. If that transfers the problem it points to the pickup. I provided the Forgotten Error with equal length HT leads for just such a paddock test eventuality.

Does the front header get good and hot. Definitely running on two at idle (try pulling the front/rear plug lead off). I once rode my old K2 a surprising distance two up with panniers on one cylinder.
mbmm350s
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Re: Its a mystery

Post by mbmm350s »

Hello Ted
Does the front header get good and hot. Definitely running on two at idle (try pulling the front/rear plug lead off). I once rode my old K2 a surprising distance two up with panniers on one cylinder.
I have had this fault on three occasions in the last few years. bike would start and appear to idle correctly but until about 2500-3000 rpm was only idling on one cylinder only. The spark appears good outside of the engine, but is weak/intermittent and killed by the compression, The fault on all occasions was the pick up unit, the trigger pulse voltage is dependent on engine speed and is quite small. Difficult starting may indicate a degraded ignition generator winding but i think this is less likley in this case. It is very difficult to spot the fine cracks that occur in the pickups and eventually cause the winding wire to break, often though not always the engine drops onto one cylinder when hot.
Very late ignition timing or non existent spark will cause lower than expected vacuum reading, overly advanced the opposite.
Like 72 degrees says - the engine can operate quite happily as a single, so for diagnostics remove one spark plug in turn.
The whole ignition system is not helped by poor earths so definately worth checking these particularly around the headstock area.
The pickup itself doesn't have an earth and relies on continuity through screws to the engine case.

Can you confirm it is the black type Pickup unit with grey or beige transducers i.e standard setup for X3
pictures are here https://www.motomoriniclub.nl/tech.html replacement transducers may be black.

Vacuum take of carb inlet rubbers wasn't provided on X3 Kanguro, as the HS carbs have the vacuum take off tube one of which is teed off for the vacuum tap, so this has been modified? And to be sure any unused vacuum port is blanked off during testing or that will kill the vacuum reading and that there is no connection between the two cylinders inlet manifolds.

After all that it will probably turn out to be a carburettor fault!

Mark
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72degrees
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Re: Its a mystery

Post by 72degrees »

mbmm350s wrote: 08 Feb 2022 09:29 Hello Ted
Does the front header get good and hot. Definitely running on two at idle (try pulling the front/rear plug lead off). I once rode my old K2 a surprising distance two up with panniers on one cylinder.
After all that it will probably turn out to be a carburettor fault!

Mark
On a Morini it's always ignition - except when it's carbs ;)

I have lent my spare known good red type II pickup to a couple of folk as a diagnostic. I know that there is one combination of pickup/transducers that is 'wrong' but will still run. I discovered this on the car park of a 'Mr Bed' hotel on the outskirts of Rheims - after the impromptu K2 175 single journey. The K2 was black pickup and grey transducers but I had borrowed the red/ 1 black items from the 2C as a precaution (prescient or what?). Can't remember which it was, but one permutation brought the dead cylinder back to life along with a functioning second one. Got us home though clearly running a bit 'off' ignition timing wise.
MickeyMoto
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Re: Its a mystery

Post by MickeyMoto »

I used to work with somebody who said in regards to fault finding that it is always something silly... unless it's not.

Or, another colleague who used the trusty poke and hope method.
3potjohn
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Re: Its a mystery

Post by 3potjohn »

Thought I had responded but maybe did not submit.I should have a good black pickup which you could borrow to try if that is your variety. Think some on Mdinas website if it proves to be the issue. Nothing trapped under that fat tank?
Some distance away but could send via some secure postal system. Bit odd that it only followed your earlier fettling.
Ht leads screwed in properly?
John
Ted.3593
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Joined: 01 May 2019 22:13
Location: Chesterfield

Re: Its a mystery

Post by Ted.3593 »

Thanks folk for the help and advice, I'm confident there are no air leaks. Even though I removed all the gasket cement some animal had used when fitting the carb rubbers, so much it was dripping into the carb throat ! (No none caused any blockages) And as the transducer ,plug and HT lead have prooved ok on the other cylinder I can see I need to look into the condition of my pick ups (and again quality of any earths). Mark you've reasured me I wasnt going round the bend, I'd had a conversation with a very qualified engineer where I'd suggested the low vacuum may be caused by a retarded ignition.Needless to say I told I was talking a load of rubbish and sent away with a flea in my ear. And the front exhaust is nearly cool enough to hold when the rear would have your skin off !
John tank is off and she's running on a remote tank.
Should get some time to have another fiddle about after the weekend, will update then .
Thanks again Ted
lemans
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Re: Its a mystery

Post by lemans »

worn down inlet camlobe of rear cylinder.
check valvelift while slowly turning the engine over by hand
Ted.3593
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Joined: 01 May 2019 22:13
Location: Chesterfield

Re: Its a mystery

Post by Ted.3593 »

Well i finally got some free time to look at the bike.Mark you where right there were cracks in the pickup casing with the addition of heavy gouging to its inner surface caused by the magnet breaking up as it span by! Reckon its bust.
As the old saying goes, if you've got a carb problem start by looking at the ignition.
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