350 K2 re-commissioning Part 2

[penman]

Well yesterday was a bit of a milestone, my UK registration came through for the Morini so today I was able to take it for a ride. I did about 40 miles and there's an awful lot to like about this bike! It also threw up a couple of problems, not unexpected.

My clutch problems improved all the time I was riding. I can't say it's a good clutch, but it is tolerable now. I still can't get neutral at rest and gear changes are still a bit clunky, but much better. The clutch is still a bit sharp, almost snatchy. I can live with that for now, especially as it seems to be improving.

I seem to have a big fuelling problem. I first thought it was a flat spot in the 4 to 5000 rpm region, but I am beginning to think the trouble starts as soon as I get into the power circuit - it's fine on the pilot circuit, i.e. up to about quarter throttle. As I started to open the throttle further it went very flat and actually felt like fuel starvation to me. But if I change down and push the revs up, it does start to pull strongly again when you get beyond 6000 rpm, even with the throttle on the stop, and I saw over 90mph in 6th (accidentally!). When I got home I did have a look at the plugs:



I think they look too pale, indicating a weak mixture - can anyone else comment? I'm not very familiar with this engine yet! If this was a 1960s British twin, I'd be worried I might hole a piston with plugs that colour!

I did wonder if the fuel cap breather was blocked, so I rode with the cap loose for a few miles. It made no difference. Any ideas?

To end with the good things, I find the bike light and surprisingly comfortable. It turns in really easily and feels nimble and sure footed - a great pleasure on country roads. The fairing is surprisingly effective and you feel pretty well protected from the wind at 70 mph. The rear shocks felt a bit soggy at first, but either that's another thing which improved or I got used to them. Either way, I felt they were doing a pretty good job by the end. The footpegs are a touch too far forward but it's not serious.

Now I just need to get this flat spot issue sorted. Now that I've discovered how to post images, here's a photo of the bike looking cheerful in the sunshine:



Regards,
Joe.
p.s. Why is there no trip on the speedo?

[MickeyMoto]

[/quote]
p.s. Why is there no trip on the speedo?[/quote]

Being a Vagueliar it will just tell porkies, so why bother? I like a trip for fuel purposes.

The later bikes had a trip. Try a Kanguro or Excalibur. Not sure if the drive gearing will be OK.

[EVguru]

The body of the plug is black whilst the nose is light brown. It certainly not white or glassy, so I'd not be too concerned.

You really can't tell much from plug colour unless you've done 'chop', riding at constant throttle and load, then pulling in the clutch and killing the engine.

What grade are the plugs? I run BP7ES and the plugs will always be black (but not sooty) when I remove them.

[penman]

No I didn't do a plug chop, that was after some mixed riding, the last couple of miles being in traffic. Both plugs are the same pale colour. They are BP7ES. I don't know this engine well yet, but generally I would expect them to be fairly dark after a couple of miles in stop start traffic. The insulator is practically white and the electrodes just have a tiny bit of very pale brown deposit. By the mid '80s though, they were moving to leaner running I suppose, so I'm not sure.

I'll try raising the needles one notch. I'm also wondering about fuel level in the carbs. I have fitted the new white floats and I see they are 12.5g against the 14.5g of the earlier black floats - is the 10mm setting the same, or will that result in a lower fuel level in the carb with the white float (presumably) riding a bit higher? I didn't alter the float setting, they were about spot on the 10mm when I checked them.

I'm not sure I'm thinking quite logically here - is there a clue in it coming back to life at higher revs? I did have to nurse it a bit to get up there, but once past 6000 it was pulling like a train.

[EVguru]

Leave the needles alone. These are carburettors, not AMALs.

Ignore the 10mm float setting. Use the information in the Dellorto tuning guide, it's easily found online.

[penman]

Haha, side-swipe at Amals noted! Actually, I'm quite a fan of Mk II concentrics which are trouble-free if correctly set up and the wacky jetting of previous owners is put back to that given in the Amal tuning guide. The same applies to Mikunis and I'm guessing it is the same story with the Dellortos. As it is, the jetting of my carbs is different to that given in the Dellorto document and different again to that given in the Blue Book - I don't know if mine is right or wrong. I also don't know how a 258BD emulsifier (mine) differs from a 260CM (Dellorto guide) or a 260BD (Blue book). Similar story with the needles. To add to the uncertainty, my bike is a US export model, which does appear to have different carburettor settings - but are there other differences to allow for leaner jetting? I don't know! Different cam? Different CR?

With this degree of confusion, you can understand my idea of raising the needles one notch to see if that makes it better, worse or no different. If it seems to improve things, I'll know that it's a bit lean on the power circuit, so I might invest in new main jets - mine are 108, Dellorto and Blue Book give 112. Trouble is, I feel I'm poking around in the dark here with all this conflicting info! Maybe I need to change the main jet, emulsifier tube and needle as a set. And these Dellorto parts are all so expensive!

Anyway, thanks for your comments and the Dellorto set-up for those white floats, I hadn't found that, but I have it now - you never know, that might fix it!!

By the way, do you know if the US models do differ in any other way apart from carb set-up? I'm talking about the engine here, not lights and handlebars!

And to end on a positive note, the Dellortos give excellent cold starting like all these plunger-type enricheners.

[Ralph]

If that's a new exhaust system you may find the
flat spot disappears as you get a few mile on the clock
for a trip I have a cheap cycle computer it gives miles
speed, ave speed and so on spot on once ajusted and only a few £'s

[penman]

No, these are not new exhausts, and this is more than just a flat spot unfortunately.

Thanks for the idea of using a cycle computer for a trip, I'll give that some thought - I guess it would be possible to make it quite unobtrusive and they have all sorts of features you wouldn't normally get without a full trip computer as on modern bikes. On my classic bikes I normally reset the trip when I fill the tank, but if I'm touring or attending a rally it's useful anyway. Not the end of the world, but a rather surprising omission on a 1985 bike I thought.

By the way, I checked the float heights yesterday, using the diagram on the Dellorto website. This calls for 24mm +/- 0.5mm from the carb body to the outside edge of the white floats with the carb face down (intake side down) on the bench. Mine were just about 25mm, so I have made that minor adjustment. I doubt if that is enough to account for the major problem I'm seeing. I have also raised the needles from the middle groove to the bottom one. This will bring in the main jet slightly earlier as the throttle rises, making the first part of the power circuit a bit richer. If it makes no difference or makes it worse, I'll know that isn't the problem. If it improves things, I think I'll have to change the main jet, needle and atomiser to the UK spec sent to me by the man at Dellorto. The current setup doesn't line up with any spec or list that I've found, so of course I don't know if it's right or wrong. A pain in the neck! I didn't get a chance to test it yesterday due to thunderstorms! And I won't get a chance today either. Frustrating!

I'll have it going properly in the next week or so one way or another!

[Ming]

You mention it's a US import - I think they may have been jetted differently. Have you looked on the Dutch website?
http://www.motomoriniclub.nl/carb.html

[penman]

Thanks for thelink to the Dutch website. That is the same info I got from Eurocarb myself. I do think the US models were jetted differently, probably to conform to US emissions legislation - but presumably the bike still worked! The Blue Book does give different jetting for US models, but it differs from my bike as well as from the Dellorto data. This is why I feel as if I'm poking about in the dark!

What I don't know is whether there were any other changes to US bikes to allow them to work with leaner jetting. If anyone has any information on that, I would be very grateful. Also, if anyone else has a US bike which is running well, I'd love to know what carb settings they have - jets, needles and emulsifier.

It's quite possible that a previous owner has been playing about with the carb setup and has created the problem I am now seeing, but I have no way of knowing that unless I can find reliable data. For all I know at the moment, the US bikes may have had a different cam, lower compression or whatever. One thing for sure, it's running very badly and the symptoms point to a fuelling issue, so something's wrong.

I'll post again as soon as I've had a chance to test it with the needles raised.

Many thanks to those who have commented!

[pedro]

Just a thought, you seem very clued up so I'm sure you have already eliminated this, but air leaks on the intake side could account for this. The rubbers between carb and head and also between carb and air filter have been known to split with age, in fact some new ones are rubbish. Best of luck.

[MickeyMoto]

I thought the US models had the mixture screw blanked off? Was there anything in the downpipes? The most polluting country in the world strangled bikes!

[penman]

I think the rubber connectors either side of the carbs are in good condition, but it's a good point, I'll double check that. Worth checking that the jubilee clips are tight as well.

My mixture screws were not blanked off. I've seen that on US made lawn mowers - not exactly blanked off, but sealed with a plastic seal. I do need to have the pilot mixture screws 3 turns out, which seems a lot to me, but it starts, idles and runs well up to about quarter throttle, when it goes very flat, misfiring and weak. It all starts to improve if you manage to nurse it up to 6000 rpm and from then on it pulls fine on more or less full throttle.

If we have anything like a dry day tomorrow, I'll give it a run with the needles raised a notch and see it it's any different.

[penman]

Well I checked all the air leak possibilities but everything seems OK. So I took the bike out for a ride, the only difference being the throttle needles raised one notch - i.e. in the bottom groove instead of the middle one. This has improved things quite a lot although it hasn't eliminated the problem by any means. What I am seeing is that I can be accelerating strongly in (say) 3rd gear, then I go to change up and the engine dies. In fact if I de-clutch and shut the throttle, the engine actually stops. If I do a normal up-change, there is a lengthy lag before the engine starts to pull again. If the revs are higher than about 6000, this doesn't happen and it will pull strongly right away. Also, if I give it full throttle (right to the stop) it will always pull strongly. at any revs. I haven't done a plug chop, but the plugs are always very pale, even after slow running in traffic. Finally, if I keep below about quarter throttle it behaves fine - though of course this may not be enough for the road conditions.

Just to eliminate any other factors, I've re-checked ignition timing and valve clearances and I checked that the valve timing is correct according to the timing marks. I have new air filter elements and fresh 97 octane petrol. The engine starts very easily hot or cold and it idles very well - I must admit it idles a bit fast when hot, but it's not ridiculous.

My cautious conclusion (and I'm by no means sure that I'm right) is that it is running too weak on the power circuit - i.e. main jet active. This is based on the pale plugs and the fact that raising the needles has improved it somewhat. This conclusion is a bit speculative and even I can think of arguments against it! Anyone got a better idea?

As I've mentioned before, I don't really know if the carburettor setup is correct for a US model 1985 K2. Unless anyone has a better suggestion, my next move will be to change it to the "European" K2 setup, which is a different emulsifier, needle and main jet. I don't intend to change the pilot jet at this stage, since the pilot circuit seems to be performing OK.

I love the way this bike handles, and it weighs next to nothing, so I need a brilliant suggestion to help me nail this problem so I can enjoy riding it!!

[EVguru]

Just a thought, but do you still have the balance pipe between the two carbs in place?

It's possible to get the bike to run without it in place, or with a leak, but it can give some of the symptoms you're experiencing. A clue would be that the idle speed screws are barely (if at all) lifting the slides.

I normally remove the balance pipe and cap the vacuum ports. I find I get better low throttle response that way.