Trying to get beloved Sport back on the road- poor idling

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Re: Trying to get beloved Sport back on the road- poor idlin

Postby 72degrees » 08 Oct 2017 19:03

They often go AWOL. The main thing is they are black ones.

I think when the Dutch club say 'width' it perhaps means the length of each metal strip. So that definitely looks like a compatible early red pickup and rotor.

To be fair, my 375 wasn't idling that reliably today on a VMCC run. The Treasurer's electric start Strada was even worse, so I advised him to just screw in the throttle stops a quarter of a turn each side. A bit fast at approaching 2000, but it prevented it stalling.

When I think about it, the 'racer', which idles so well, also has almost brand new (PHBH28) carbs on it.
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Re: Trying to get beloved Sport back on the road- poor idlin

Postby Long_Road » 08 Oct 2017 19:23

'They all do that sir'. Yes I wonder if a lot of Morinis don't idle as well as they used to. I guess PHBH28 carbs are a more modern design too which helps.

It appears everything igniton-wise is correct. The bike itself does seem to be quite original and unmolested. Well, until I started on it anyway...
'I'll get you to idle if it's the last thing I do'
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Re: Trying to get beloved Sport back on the road- poor idlin

Postby Long_Road » 09 Oct 2017 20:48

Now obsessively reading up on 3 1/2 ignition.

My transducers' model no. is 32392, whereas I read that all Ducati's transducers for the Morinis started with 322--. The given model no. for the 350 black, green dot transducer with red pickup is 32292, so I would guess that my ones are, despite the discrepancy, correct.

Finally managed to get a resistance for the stator - 286 ohms, which is impressively good. AC voltage at idle is 77 volts. Tried a spark test again and actually, they are strong and blue - I was wrong before.

I will check and clean the relevant connectors next. I wonder if this is pickup or transducer related.
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Re: Trying to get beloved Sport back on the road- poor idlin

Postby Long_Road » 10 Oct 2017 17:14

Excuse me - have just read that Morini transducers are in fact 323--- part numbers, and mine (323921) are the correct ones for the early 3 1/2s. I'm an idiot - didn't see the '1'.

Going to have a conversation with North Leicester Motorcycles.
'I'll get you to idle if it's the last thing I do'
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Re: Trying to get beloved Sport back on the road- poor idlin

Postby davel182 » 10 Oct 2017 17:21

The numbers of the various transducers are on the Dutch site. The number for the 350 (black with red pickup) is 323921. If you got the 322 prefix from Soren Hansen's video, I think that's just a typo.
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Re: Trying to get beloved Sport back on the road- poor idlin

Postby Long_Road » 23 Oct 2017 18:51

I think I may have made a breakthrough; the old girl is idling better than she ever has, since I first bought it some ten years ago. I’m doing my best not to get over excited – I still need to have a decent ride – but it’s progress.

I had a conversation with NLM about my problem and Stuart was very concise. In essence, I learned that:
a) the ignition timing (which was set 34 degrees too advanced; set correctly now) is probably a red herring
b) the Dellortos are very sensitive, and
c) float level adjustment is not as accurate as the book makes out.
I have told him before that he should write a book on the Lambertini V-twin – his passion is contagious. Spurred on, I moved my attention back to the carburation. The idle jet passages looked clear, but I did notice that the emulsion jets were what I believe to be modified 260Ks. They seem to be okay for the moment so I’ll go back to them once the bike is on the road.

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Another interesting discovery is that the mixture screws had a slightly different profile, which may explain why they needed a different amount of turns. Exact adjustment of these is crucial for a decent idle and pickup. I found a matching spare and swapped them over. I later discovered that this tiny difference did have an effect.

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I still wasn’t having much luck with the idle; the speed would change – hunting fast and slow, and eventually slow to a halt. Giving a good revving would increase the idle speed to 2000rpm, and then it would slow to 1700. A quick blip would kill the engine immediately. Over the past few weeks I had moved down to smaller and smaller pilot jets with no real effect. Remembering this I thought ‘what the hell, I’ll go back from 40 right up to 50. If it makes no real difference I’ll know it’s not the pilot jet’. When this was confirmed I moved to the last adjustable component I thought would affect the idle – the float levels.

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Re: Trying to get beloved Sport back on the road- poor idlin

Postby Long_Road » 23 Oct 2017 18:56

Remembering what Stuart said about adjusting the float levels, I came up with a basic means to measuring the actual amount of fuel in the bowls. Having just a basic setup in the garage I had to improvise with a toddler’s cup marked with pencil(!) but some kind of measuring vial or jug would be more suitable. This method showed me that the L/H carb had more fuel in it, despite me recently setting both floats to the same 11mm from the centre of the float. I then measured and lightly scribed a line to intersect the mould line of the float – not super accurate, but this would give me a consistent reference point for all the float level adjustments I was about to make.

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I dropped the levels way down to a measured 16mm to start with, and found that no fuel would enter the bowls. Okay, let’s go up. 15mm and the bike started and ran better than I could have hoped – I could feel with the throttle that the carburation had improved at low revs, and for the first time I achieved a stable tickover! I may at this point have performed a small dance.

Then came the fine tuning. Wow, these carbs are much more sensitive than their Japanese contemporaries – one example, ½ a turn on one of the mixture screws and the engine slows to a halt within 10 seconds. It was at this point I tried one of the different mixture screws mentioned earlier just out of curiosity and there was a noticeable difference in behaviour, it needing a different adjustment to the one I swapped it with. I ploughed on and half a tank of petrol later found a combination which seems to do the trick:

Pilot, 45
Main, 112
Slide needle, middle slot
Fuel mixture screws, 2 turns

This applied to both carbs, but I found that I needed to set the individual float heights differently (L/H 14mm, R/H 13mm). I believe this is due to the L/H carb being tipped at more of an angle, causing the pilot jet to be submerged further than the R/H carb’s.

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Re: Trying to get beloved Sport back on the road- poor idlin

Postby Long_Road » 23 Oct 2017 19:01

In conclusion, what I think may have been happening to cause the poor idle is the fuel levels were too high, meaning fuel was making its way past the pilot jets and filling the idle/low speed circuit, causing the mixture to be too rich at the low air speeds at idle. Give it a good rev and the excess fuel clears, allowing the bike to idle for a short time before the float bowl refills. What is interesting is that I have needed to set the float levels a fair bit lower than what the manual recommends. A glass or clear float bowl would be an extremely useful tool for setup in this respect – I’d be very interested to see what’s happening in there whilst the bike is running. The Dellorto VHBs, in combination with this small-capacity engine with no flywheel, are very sensitive to adjustment; it sometimes felt like I was tuning some kind of musical instrument, which in some ways it is…

A few other things worth mentioning are that I replaced the spark plug caps with the basic metal terminals, as I believe this is how the Morinis ran back in the day. I wanted to try removing any resistance from the spark, and these were cheap. Perhaps I’m getting a slightly stronger spark at very low engine speeds; perhaps they make no real difference.

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I splashed out on a Morgan Carbtune a few years back, and it has been very useful indeed in setting up the Morini 3 ½. It’s worth getting the carb balance absolutely spot on with this bike, as well the carb tuning.

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The last thing worth mentioning is the o-rings for the adjustment screws that come with the carb seal kits. I didn’t fit the mixture screw ones, but did fit the idle screw ones. I think the latter do play a role in preventing air leaks.


I need to give a decent road test first, but at least I’m on the right track now. Thank you very much everybody for all of your ideas and input in this particular thread. My Morini is ‘the special one’ in my garage and it is a very big deal for me to reach this milestone. All being well we will be back on the road next spring.

Chris
'I'll get you to idle if it's the last thing I do'
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Re: Trying to get beloved Sport back on the road- poor idlin

Postby 3potjohn » 23 Oct 2017 21:02

That's is good news.well worked through. I must have been lucky with mine,though having gone down a size or two? 43 I think, for the idle jet it removed any stumbling. I have always had a good tickover.I've tried to get the carbs as vertical as you can, at least not tilting inwards or outwards.Certainly on my other bikes which both have twin carbs I get them equally vertical. I can measure to fuel voumes using a glass 10 mL measuring cylinder.
As to the plug caps, I regrettably replaced mine with NGK resistor caps and cannot find my originals anymore.
Anyhow well done.
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