Time to get the K2 out of the naughty corner

[penman]

Hi everyone,

I've been busy with other things all summer, but now I think it is time to have another look at sorting out the poor mid-range running on the K2. There is quite a saga recorded in the thread "350 K2 re-commissioning Part 3", but to summarise, the situation is this:

1. The bike starts and idles very well, hot or cold.
2. Both cylinders have a good strong spark and both show normal advance with rpm.
3. Both cylinders have good compression and are identical.
4. The carbs have been thoroughly cleaned and all jets, emulsifier, etc. replaced.
5. Up to about quarter throttle, all is well, the engine pulls strongly and evenly.
6. In the mid range, from around quarter to three quarter throttle the engine mis-fires badly and if you de-clutch and close the throttle, the engine stops.
7. After stopping as in 6, it is reluctant to re-start, though once running, it's fine (though the mid-range problem is still there!)
8. If I put the throttle right round to the stop, the mis-firing gradually clears and the bike starts to accelerate quite strongly and smoothly (for a 350) right up to an indicated 90mph.

To me, this seems like a fuelling issue, I'd say it is too rich in the mid-range and is bogging down. However I've also been told that this is "definitely" an ignition fault. I'm prepared to believe that, though I'd like to understand it! I've carried the strobe with me and re-checked the timing on the roadside at the point when the fault's active, and everything looks fine on both cylinders. I don't think the problem is related to temperature or to the length of time I've been riding for. By the way, I've eliminated fuel starvation as a cause.

Any ideas out there? Please ask any questions you like!

Regards to all, and thanks in advance,

Joe.

[George 350]

Hi. What size pilot jets do you have? Years ago my Sport had a mid range misfire which was almost eliminated by using 43 pilots, down from the standard 50's. It was running around 11:1 afr prior to this at 4500 - 5000rpm. Also it is worth checking your float heights aren't too high.
Also, have to ask if you still have standard air box and exhausts, and do you have the breathers venting externally or into the airbox? Last question is whether the carbs have the balance pipe betwen them or not, or are theports blanked off?
Hope that this helps. George.

[penman]

Hi George,

Thanks for your reply and for giving me questions to think about! Currently my jetting 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 have encountered some differing versions of the recommended jetting! The float height on the new type floats is not easily adjustable, but I have tried varying it up and down with no detectable effect. I've also changed the needle height and needle type - I've tried E17 and E24, but it makes so little difference, I suspect there is a bigger issue hiding it. If I changed the needles on my Bonneville from bottom to top groove it would make a huge difference!

The balance pipe is a puzzle. If I remove it and connect vacuum gauges, the idle speed increases a bit. If I put the balance pipe back, the idle speed drops a bit. I've tried it with the ports sealed, and with a long or short balance pipe - it makes no difference to the main problem. I have repeatedly checked for air leaks in the inlet area and of course I've re-set the valve clearances.

I have the standard airbox, with all the breathers going into the airbox via a "collector" box. Currently I have the rubber seal removed from round the edge of the airbox lid. This about doubles the air intake area. I've tried it both ways though and again it makes no difference.

I should have mentioned, this is a US model, imported from California. It is very low mileage at about 3000 miles, but it has been kicking around in a shed or garage for decades and has picked up quite a number of cosmetic scars. I was planning to make a start on the cosmetics this winter, but I'm not spending another penny on it until I've got it running properly!

Hmm, now that you've mentioned breathers, I think I'll check all that for leaks, though I think I'm clutching at straws here!

As I said, I haven't dismissed the possibility of an ignition fault, but I'm not sure I can explain these symptoms by ignition.

Regards,

Joe.

[smotorboy]

Sounds like fueling is too lean in the midrange to me,,, but first things first:

What type of misfire????

1- silent misfire with black smoke and black sparkplugs means it is way too rich, and a weak spark means misfiring more at large throttle openings than at small throttle openings if the mixture is proper thru the throttle ranges... and weak spark combine with a too lean mixture work together to create massive misfire (Rich mixture light off must easier than lean mixture)

2- misfire with popping in the exhaust means Ignition breakdown

3- misfire with popping in the intake (Carbs) means it is way too lean.

If you have working chokes,, try pulling them on slightly when it is misfiring and that should tell you..

Good luck,
Robert In California

[penman]

Hi Robert,

and thanks for your comments. Let me try my logic on you - and don't hesitate to shoot me down if you disagree! What I am calling a misfire feels like the engine is constantly stopping and starting, the bike is snatching and jerking in the region of 4000 to 5500rpm. with the throttle around a quarter or half open. If the mixture is too lean, I think it would recover pretty well instantly if I change the throttle setting to a richer point. As it is, it takes several seconds to smooth out when I give it full throttle and I'm guessing that's the time it takes to clear the rich mixture. I may well be wrong though!!! The plugs are darkish, but not sooty. Also, if it was too lean, I think that closing the throttle and de-clutching would make it simply drop down to idle rather than the engine stopping and then being hard to re-start. There is no popping in the exhaust though and no spitting back through the carbs.

When I first got the bike, I had the magneto winding on the alternator re-wound and the output is now very good. I get a very good spark on both cylinders, in fact a brighter and bigger spark than I'm used to seeing on other bikes. This is in air of course, not under compression. As I mentioned, the advance seems pretty well spot on, reaching max advance at about 4000rpm. I can't see an ignition fault causing a weak spark in the midrange, but getting better if I open the throttle - I'd be delighted to be proved wrong, but I've no "spare" pickup or transducers to substitute, so I would need a convincing argument to make me start buying these expensive parts.

I will try putting the choke on as you suggest, that's a good idea. These carbs have the plunger-type enrichener, which will be less effective on an open throttle, so hopefully that will just richen it a bit, which should make it even worse if it's too rich, or a bit better if it's too lean. If the weather's OK tomorrow, I'll try to find time to try that.

Regards,

Joe.

[George 350]

Hi Joe.

Max advance at 4000 sounds a bit early. Mine have always maxed out at around 6000-6500rpm. Could your issue be too much advance lower down the rev range?


One other thing to suggest is are you sure that all the airways in the carbs are clear? If it has stood for some time, especially with 'ethanoled' petrol in the carbs, corrosion may have caused a blockage somewhere.

Whereabouts do you live? It is possible that another Morini owner lives nearby and you could try another pair of 'transducers' or carbs to help eradicate one or the other.
Edit:
I see you are in MK. I'm only about 15 miles away in Northampton, and have just installed a new NLM ignition onto my bike, so the old transducers and pick-up are still on the garage floor. These are working 'OK', just don't get as much advance on one cylinder compared to the other hence the NLM system, but they do still work.
PM me with your phone number and I can try and meet up with you to give you some assistance?

Regards,
George.

[Daddy Dom]

To me, this seems like a fuelling issue

I would have sworn the same while mine was showing exactly what you've described. However, a new pair of NLM transducers fixed that particular fuelling issue.
HTH, DD

[penman]

George:

I will certainly take you up on your offer! The carbs are absolutely clean, all drillings, etc have been thoroughly cleaned and all replaceable parts (jets, etc) have been replaced - at great expense - Dellorto parts are not cheap!

I'm not sure about the max advance point. As a general rule, there's little point in advancing above about 4000 rpm, but this engine is not what I'm used to, so there may be some difference that I'm not aware of. I'll check it again though in case I've forgotten - it was some months ago. What I do recall is that it advanced neatly to the line, so the advance range was certainly correct.

Daddy Dom:

Interesting! I still can't see how opening the throttle can make the ignition work better, but I am more than prepared to try substituting the ignition parts. This bike uses the black pickup and grey CDI units. I have seen the circuit diagram of the CDI unit online and I was quite happy to make some - it's a simple circuit. However, a few basic measurements show that the grey ones I have are different to that diagram. Without breaking the units open, I can't tell what the difference is. I did obtain one of the NLM pickup units, but it doesn't really fit on this bike due to the tacho drive and support bearing, so I had to send it back un-tried. Once again though, it measured quite differently to the original pickup.

As I say, I'll follow up on George's kind offer as soon as I can.

Regards,

Joe.

[penman]

Hi All,

I'm not going to get a chance to go out on the road today, however I did get as far as the garage and I put the strobe on the ignition again. The front cylinder reaches max advance at just about 4000 rpm according to the bike's tacho. It's tricky to see exactly where the timing mark stops moving, but it's definitely all over by 4200. The rear cylinder though has me slightly worried. The advance range is much narrower on the flywheel and it never reaches the timing mark, if the mark is at 34 deg btdc, I'd estimate it is stopping at about 29 deg. Again, there is no further advance beyond about 4000 rpm. I think the difference between the cylinders is a bit too much to be comfortable with, though having said that, the engine revs freely and it is quite easy to see 90mph in top gear. I am fairly sure that last time I checked this, the difference was a lot less, just a couple of degrees.

The front cylinder stops advancing about 1 degree past the mark, which is what I remember from last time I checked this, and I was sure the rear cylinder stopped about 1 degree before the mark - now it stops 4 or 5 degrees before the mark. Hmm, I only warmed up the engine for about a minute or so at idle and the blue book does stress checking the timing with the engine fully warm. I don't know if that makes a difference, or if it's just advice against revving a cold engine. I need to repeat this test with it fully warm.

I can try swapping over the "transducers" to see if the timing imbalance swaps as well. That should tell me if it is due to the pickup or to one or other transducer. I have a strong feeling that this is not the cause of the main problem, though it does seem to indicate that all might not be well in the ignition area.

Regards,

Joe.

[EVguru]

The balance pipe is a puzzle. If I remove it and connect vacuum gauges, the idle speed increases a bit. If I put the balance pipe back, the idle speed drops a bit. I've tried it with the ports sealed, and with a long or short balance pipe - it makes no difference to the main problem.

That's sounding alarm bells right there, unless you've got your description back to front.

The balance pipe ports are on the intake valve side of the throttle slide. Air entering these ports is bypassing the slide and would raise the idle (assuming it's not now too lean to run).

Connecting vacuum gauges to the ports effectively blocks any air flow through them and results in a slower idle. Re-fitting the balance pipe then allows a bit more air to flow from the opposite side and idle jumps a few hundred rpm.
I think they were fitted to make the setup less sensitive to ham-fisted carb synch, or as part of the emissions control for US model. I've always got best running by blanking the ports off and carefully balancing the carbs.

Removing the balance pipe and leaving the ports uncapped results in air bypassing the slide and should result in a very high idle. I fixed a bike at the MRC Rally/AGM this years that rode in that way with just a pair of pipes vented to air.


The Dellorto tuning guide is readily available on-line and will give you some idea of which fuel circuit is active at different throttle openings.

When it comes down to it, time spent on a rolling road can be very cost effective. I've seen people spend hundreds of pounds on jets etc. chasing a fault which could have been diagnosed with a single Dyno power run. You need to use a Dyno with ignition analysis kit because an ignition fault can show up as an incorrect mixture due to un-burnt fuel.

[penman]

Hi Paul,
Yes, we had the balance pipe discussion earlier in the year, before I abandoned this project for the summer, that's why I referred to it as a "puzzle". The pilot mixture screw is about 2 turns out, which I gather is more than normal, so perhaps something is happening to make it leaner than it should be. I don't know what that can be however, there are no air leaks and all internal carb passages, jets and so on are definitely clear. At the moment, on your advice I have the vacuum ports sealed.

George has just loaned me a red pickup and matching black "transducers" for a substitution test. I fitted them this morning, but frustratingly I haven't had time to test the bike properly. It starts, runs and idles fine - but of course it did that much before! Hopefully I'll get a chance to test it properly tomorrow. I would like to eliminate the possibility of an ignition problem before tearing the carbs off yet again. Even better, it would be great if swapping those ignition parts cures it, I'm past caring if I really understand why!

I've just returned from the Moto Piston Rally in Northern Spain, and I had some interesting chats with some Dutch Morini enthusiasts who said this is "definitely" an ignition fault, though they were unable to explain exactly why. So, I'm greatly obliged to George for the loan of the pickup and transducers, I'll report the results tomorrow with a bit of luck!

Regards to all,
Joe.

[penman]

Well I managed to get out for a quick test run this morning and I'm disappointed to say that swapping the ignition hasn't made any significant difference to this problem. I suppose that has at least eliminated ignition as the cause.

There are two strange symptoms which I think I need to concentrate on now:

1. The pilot mixture screws are set to 2 full turns out and even if I unscrew it another turn, it doesn't run badly or start to slow down, though the screw is in danger of falling out! I'm told a normal setting is one turn or less, so something odd is going on here.

2. If I fit a balance pipe between the vacuum ports on the carbs, start the engine and then seal the pipe by flattening it with pliers, the engine speeds up slightly - I'm told it normally slows down if you do this.

Both these details seem to point to something making the mixture too lean, and it is affecting both carbs equally. I'm confident that there are no blockages in the carbs, all the jets are new, and there are no air leaks in the inlet area. There is virtually no wear on the throttle slides and they are going right down to the bottom OK. I'm running out of ideas here, any suggestions?

I suppose I should put all the jetting back to what it says in the Dellorto guide before I swap the ignition back, and also put the needles back to the correct groove (centre?) but I'm not optimistic that that'll make any big difference. I'll do it though, it'll be another question mark eliminated.

A final question. A number of people have mentioned mid-range flat spots as something you learn to live with. How bad are these flat spots? I'm not trying to fix a problem which others regard as "normal" am I?

Regards to all,

Joe.

[EVguru]

I haven't got my references to hand, but do you have lighter than stock floats fitted?

[penman]

At the moment I have the new-type floats fitted, these are 12.5g as opposed to the earlier black floats which were (I think) 14g. I adjusted the float height as instructed by a very helpful man I spoke to at Dellorto. Both old and new floats give the same problem.

When I first got the bike, the carbs were very badly varnished up, I couldn't even get the float bowls off to begin with. Once I got them open, it was fairly easy to clean them, but I had a lot of trouble cleaning the last remnants of varnish off the floats - it really sticks well to that black plastic! That's why I replaced the floats, I was unsure how much extra weight the varnish was adding and I convinced myself that the floats were too heavy and making the fuel level too high. Needless to say, it made no difference.

Are you going to Stafford at weekend?

Best regards,

Joe

[EVguru]

I'll be on the stand as usual.