350 K2 Re-commissioning Part 3

[penman]

The previous thread had got a bit long and had drifted off into weather comparisons, a more interesting subject, I must admit!

Well I fitted the new carburettor parts and took the bike out for a spin in the sunshine this afternoon. What a disappointment! Well, it's better, no doubt, but it's way short of acceptable. The flat spot (more of a dead spot, actually) starts a bit lower down the rev range, round about 4000 now and extends up to past 5500. I can't really decide what's going on but let me describe it again. If I am accelerating in any gear, say 3rd, it is pulling strongly until I make the up-change when it just gives up, mis-firing and the speed drops and drops. To get out of this, I can change down, when after a few seconds it will start to go again. Or I can twist the throttle right round to the stop when it comes back to life and pulls strongly. When you go to full throttle, two things happen - the needle rises giving you the maximum flow of fuel, and the slide rises giving you the maximum flow of air. Or does it? The air flow also depends on the suction in the inlet ports and the fuel flow depends on the depression in the venturi. I confess I don't really know what's going on here, I'm not sure if full throttle gives you a richer or leaner mixture - or has no effect on mixture.

Whatever, I'm not used to bikes which need this amount of fine tuning to achieve acceptable performance (note - I'm not aspiring to "good" performance yet!). I can't believe the Morini can be this difficult, so what am I missing? Is there some other fault which would produce these symptoms? It has to affect both pots though! I've now spent £200 on Dellorto parts without achieving very much, just a small improvement and I don't feel inclined to spend any more without a cast-iron reason! My experience of carburettors is that if they are clean and have the correct jets, etc, they just work pretty well, no faffing about required. In fact for twins, I don't even bother with the vacuum gauges normally.

I haven't checked compression - I'll do that maybe tomorrow, but it's OK as judged by foot pressure on the kick-start. The ignition timing is correct on max advance and there is a good bright white spark on both plugs. The plugs look a bit pale to me, but probably within the acceptable range. No other signs of running too hot, such as blued exhausts. I've tried it with the balance pipe fitted and with the vacuum ports blanked off (no difference). I've also removed the rubber elbows on the inlet ports, checked them for damage and checked the port stubs for security. I put the elbows back with a smear of rubber lubricant to ensure they seal well. I'm running out of ideas.

For what it's worth, my current (new) carb setup is:

Float: 74502 (12.5g)
Float needle jet: 200
Throttle slide: 50
Throttle needle: E 17
Emulsifier: 260 BD
Main Jet: 112
Pilot jet: 44
Starter Jet: 50

I've changed all the washers, O-rings etc. and adjusted the float height according to the diagram on the Eurocarb website - i.e. 24mm +/- 0.5mm to the outer edge of the float. It's easy to balance the carbs (suggesting no air leaks) and the engine starts and idles very well. I don't think there is any problem while you are purely on the pilot circuit. There's no off-idle hesitation and all is going well until you get up to about quarter throttle. One last point, it gets worse as it gets hot.

Any ideas? Thanks!!

[Daddy Dom]

If you can, I would try it with another set of transducers, either new or proven to be working properly because it sounds like ignition to me. Mine used to do all that but new NLM transducers fixed it.

[EVguru]

Does your idle speed change between blanked off vacuum ports and having the balance pipe fitted?


I don't think this is likely to be a factor here, there's something else going on. The old adage is that all caburation problems are caused by ignition and all ignition problems are caused by carburation, except when it's the other way round, or both! I should have suggested earlier that a rolling road session would be a good idea. It has to be one with a good operator though. An ignition problem will cause the apparent mixture to change, so you need simultaneous monitoring of the sparks on both cylinders.

[penman]

Thanks for the responses guys, believe me, it is helpful.

Paul, as always, your experience is showing through and I think you are probably right to steer me away from the carbs now. I remember that old saying about fuelling problems always being caused by ignition and vice-versa - and wasn't there a quote from Sherlock Holmes along the lines of "when you've eliminated the probable, what's left, no matter how improbable, must be the truth"! So the finger of suspicion is now pointing at the ignition - until that's eliminated of course.

Just to dispose of your question, and try not to laugh, this is an indication of desperation, I have tried no balance pipe, short balance pipe, long balance pipe, plastic and rubber. None of this makes any difference whatsoever. The balance pipe certainly isn't "needed". Actually, the carbs aren't especially sensitive to balance either - so long as the slides are starting to rise in unison, as judged by sticking a finger in the intake you'll get let's say 98% good running in the idle to quarter throttle region - and after that I wouldn't expect it to matter much anyway - not that I'd know based on the way this one runs.

Back to the sparks. The other day I noticed the earth wires on the transducers were like this:



In fact the actual conductors inside the plastic insulation are corroded all the way along. These are plated copper, looks like nickel plate and the plating is coming off the copper, you can easily scrape it off with a thumbnail. I have replaced the wire up to a point about 2" from the transducer and put heat-shrink up to the point where it enters the potting. I am of course concerned that the damp or whatever caused the corrosion has crept inside the potted coil and electronics, so I am a bit suspicious of the transducers.

At cranking speed, I see a good bright white spark at each plug, but of course that doesn't tell you what they are like under compression - or with a higher speed of repetition. Hmm, isn't there another old saying about spark colour? Something like "white is right, blue will do but red is dead" - these old wives knew what they were talking about!

Moving on as quickly as possible, I have had the magneto winding re-wound, so I must assume that's OK for now. I think the flywheel magnets are OK because the alternator is managing 14.2v with lights on and about 4000 rpm. So, are there any tests I can do on the transducers and/or pickup? Hmm, I think I saw a diagram for the transducer somewhere, it was very simple, I guess I could make one if necessary. I'll see if I can find the diagram again.

As always, ideas and suggestions most welcome!

[EVguru]

Sorry to repeat, but

"Does your idle speed change between blanked off vacuum ports and having the balance pipe fitted?"

It should rise because of the extra air it lets in. If it doesn't rise, then perhaps there is something odd going on. I wouldn't normally expect the mixture screws to be that far out, although there are two styles, one with a short taper and one with a long.

Your earth leads shouldn't really matter as you'll have the white wire from the alternator, which is an additional earth.

The ignition boxes can break down in interesting ways. My 250 2C had a mid range missfire that would develop part way through a ride and go away if it rained! That gave me the clue that it was ambient temperature dependent. I made my own ignition circuit from the information on the Dutch website (which contains a small error) which fixed the problem (although not the misfire above 10,000rpm, which I think was alternator related). There's a correct circuit diagram on my website.

[penman]

Paul, sorry not to have answered your question properly. I just tried it with the engine warm and I ran it with the balance pipe on. I then used pliers to flatten the pipe to close it off. The engine speed falls slightly when you open the pipe - from about 1200 rpm to 1150. I spent a little time tweaking the idle mixture and speed and re-checked it with the same result. Finally I re-checked the ignition timing at 6000 rpm and I noticed some variation in the timing, the timing mark is jittering through about 3 or 4 degrees on the flywheel. That was triggering on the front plug. Is there a timing mark for the rear cylinder as well? I'll have a look. I don't know if it jitters throughout its range, it's a bit hard to tell without being able to see more of the flywheel (I'm just looking through the hole). A question. Does this system use electronic advance? i.e. is the trigger at max advance and the electronics then retards it according to rpm?

By the way, an earlier statement of mine might be misleading. I said the problem gets worse when it's hot - I should have said it gets worse the longer you ride the bike, which is not necessarily the same thing. Next time I ride it, I'll measure the cylinder head temperature, I have an IR thermometer.

I shall have a look at the circuit diagram on your website later on - I'm supposed to be cutting the grass at the moment!
Regards

[EVguru]

I just tried it with the engine warm and I ran it with the balance pipe on. I then used pliers to flatten the pipe to close it off. The engine speed falls slightly when you open the pipe - from about 1200 rpm to 1150.

That's not what I'd expect. I've found the idle speed to rise by 2-300rpm when I take the vacuum gauge off and put a balance pipe back on. It's certainly enough that I'd want to lower the idle speed and that would risk loosing the just achieved balance. That's why I just blank the vacuum ports off, so the idle speed doesn't change. I think the balance pipe was intended to make the bike less sensitive to the balance adjustment.

Finally I re-checked the ignition timing at 6000 rpm and I noticed some variation in the timing, the timing mark is jittering through about 3 or 4 degrees on the flywheel.

That's normal. Some of it will be from slack in the un-tensioned cambelt

Is there a timing mark for the rear cylinder as well?

No, but it's easy enough to create one. Use a piece of paper wrapped around the flywheel to measure the circumferential distance between the TDC and full advance lines for cylinder 1 and use that distance to create a full advance line for cylinder 2.

A question. Does this system use electronic advance? i.e. is the trigger at max advance and the electronics then retards it according to rpm?

Yes and no. Yes, the advance is electronic, but no it's not retarding from a given point. It uses the shape of the curve generated by the pickup, which changes with rpm. The Morini ignition has a very wide range, firing after TDC when kickstarting and going to around 34 degrees BTDC at full advance.

[penman]

I see, there is more to the pickup than just two coils and a spinning magnet then! I must say, it sounds like a very sound design. The problem of the "retard from max advance" design is that when kick starting, the rpm is very difficult to determine and the timing can be badly controlled, and since the only known reference point is 38 deg btdc, it leads inevitably to kick-back, not at all amusing. As soon as it's running, this approach works fine.

So, back to the point, what do I try next? I am moving away from carburetters because they are clean, I have jetting which works for other people, it starts and idles extremely well. I can't think of any reason to blame the carburetters. There is a small question hanging over this balance pipe, but I'm not sure what, if anything it suggests. It looks as if the pickup must be working, unless they tend to "go off" in some way after you've been riding for a while. I'm conscious that if I blame the transducers, it has to be both of them, which stretches credibility somewhat. I suppose both coils could be breaking down after a period of use, but I don't like coincidences!

I suppose I can easily make new transducers (thanks for the circuit diagram) and I've plenty of old but known good Lucas coils which would be good enough to prove the point without the need to spend more money. This is a capacitor discharge system and after 30 years the capacitor could easily be feeling its age, even if the coil's OK.

I'm going to Stafford on Saturday, if I see any nice compact, modern coils at a sensible price I might just get some. Apart from that, I'm out of ideas and my enthusiasm is starting to fade a bit. Clearly there's something wrong but what is it???

[EVguru]

I'll be on the club stand, so come and say hello. I should have enough spare ignition bits that I could lend you some for testing.

[norbert]

As it is a K2 I supose you have a black pickup. What kind of boxes you have, grey with a buckle?

On a trip to England and Irland with my first 3 1/2 back in the early 80ies I had problems when the motor began to get warm. It was the pickup. The red ones are a bit more sensitive I think. It took me nearly a week to find out that the problem disapered when I rode without the cover of the pickup. That way I drove home. A week later the pickup was definetly finished. It´s just an idea to try it without that cover. If you can get another pickup to try, that would be the best to be sure about that thing.

ciao
norbert

[penman]

I'll be on the club stand, so come and say hello. I should have enough spare ignition bits that I could lend you some for testing.

I'll be sure to call in at the club stand it'll be a pleasure to meet you!

well if you have spares you are happy to lend, I'll be more than grateful and I certainly won't say "no"! I see you are just down the road in Luton, so returning things can't be too much of a challenge!

Probably see you on Saturday!

[penman]

As it is a K2 I supose you have a black pickup. What kind of boxes you have, grey with a buckle?

On a trip to England and Irland with my first 3 1/2 back in the early 80ies I had problems when the motor began to get warm. It was the pickup. The red ones are a bit more sensitive I think. It took me nearly a week to find out that the problem disapered when I rode without the cover of the pickup. That way I drove home. A week later the pickup was definetly finished. It´s just an idea to try it without that cover. If you can get another pickup to try, that would be the best to be sure about that thing.

ciao
norbert

Yes, the pickup is black and the ignition units are grey. That's interesting information, I won't eliminate the pickup. Not quite so easy to ride without the cover as it incorporates the tacho drive on this model, but I could do it as a test. Trouble with this kind of fault is that you don't know how long you have to ride it for to be sure the problem really has gone away!

[norbert]

Just leave the "cuentarevoluciones" off, fix the cable to the frame. If the problem with the warm motor disapears, you have to look for another pickup

good luck!
norbert

[penman]

Well I'm still not really getting anywhere with this. I seem to have convinced myself that the fault is ignition based now, and maybe it is, but t is not really proven.

On the K2, both TDC points are marked on the flywheel as well as both max advance marks. Very handy. Both front and rear sparks are advancing but at 4000 rpm the front cylinder is a degree or two retarded and the rear cylinder is a couple of degrees advanced (relative to the max advance marks). I swapped the CDI units over and it made no difference, leading me to conclude that the two units are at least triggering at exactly the same voltage. There is no further advance beyond about 4000 rpm, which sounds OK to me. At idle speed you are well up the advance curve and at 2000 rpm there is about 1cm of the flywheel circumference to go before max advance is reached. Is it normal for there to be that amount of variation between the timing of the two sparks? I doubt if this in itself accounts for my problems, but perhaps it is indicating a slightly dodgy pickup?

Of course I can't reproduce any faulty running when the bike is stationary and maybe it wasn't running for long enough for the fault to show itself anyway.

As it stands, I think there is a possibility that the pickup is faulty. If the problem is with the CDI boxes, they both have to be faulty which seems unlikely, though it's clearly possible. I think,I need to find a known good pickup to try, so unless anyone has a better idea, that's my current plan.