Hi Knob (?)
Many thanks for your reponse.
So far I've cleaned the Dino, and did some visual inspections. It all seems in pretty good shape! Including the brake callipers, pads and disks.
I replaced the battery, and removed some accessoiry wiring which was not stock (for a battery charger and navi unit).
Next is the replacement of the shaft drive oil. Seems an easy job to me.
I've ordered new sparkplugs (expensive, allthough the Denso's are much cheaper and 100% compatible?), spark plug caps (updated version) and ET wiring. My hope is that the coils are still OK - I will do some resistance and voltage measurements later on.
Then I will bring the bike to the local bike shop for oil replacement (and both oil filters) and new brake oil.
Also I've my doubt about the fuel - it migt be in there for some years... How do I drain the petrol from the bike to pour in fresh fuel?
Any tips for additives to clean the fuel system?
Changing rear end oil is easy, only thing to pay attention is to keep the bike upright in time pouring the new oil in to get inserted the right amount of oil. Did this yesterday, as a part of 20k km service. And ofcourse the right type and viscosity oil to be used: the DN's service manual say "hypoid oil SAE 80". This kind of single viscosity oil is quite rear nowadays, so I used synthetic 75W90, same german produced oil I used many times and many tens of thousands km's in my Goldwings.
I saw the Denso plugs used on DN (and some other bikes) but somehow those did not convince me. Generally Denso plugs are used more on cars and NGK plugs on motorcycles. It just may be kind of a prejudice, but so it is settled by experience of many years. NGK plugs (those not faked chinese ones) take pretty well higher cylinder pressure common on motorcycles than some other brand plugs.
Yes the plugs NGK SIMR8A9 are quite expencive, but Honda promises those iridium tipped ones to live on DN for 50k km's (while using bike regularly ofcourse, not letting it stand for years). So price per /km in the end will not be so tremendously high.
Spark plugs will clean and so kind of "maintain" themselves while being used regularly (and not used with gasoline octane number too high!). I saw plugs got red isolators by using some gasoline E98 because of the extra octane booster added to this gas. In Europe probably you can get E95 gas and this is better, as DN will run well even on 91 octane lead free gasoline. This probably is not on sale anymore at least in EU.
Regular tip plugs (like CPR8EA9) will survive for about 10k km's. Basically it is possible to use those regular cheaper plugs also, just remember to change them in time. My friend professional bike mechanic says if engine is in good shape, it will run on any plug, so said with little humor. And if you feel you need to fix your engine by changing spark plugs - then the real culprit is somewhere deeper...
Here it seems not overwhelmingly pricy (by means of EU prices):
On older similar engines like on VT600C or XL600V (direct heritage to DN's engine) for example Honda used two spark plugs per cylinder. And demands for spark plugs were lower in this case. I see no good about dropping this practice on the newer 680cc engines using only single spark plug, thus demanding expencive and very good plugs. These Honda's V-Twin engines have quite low and flat burning chamber and igniting the fuel mixture from two places will be a better idea.
If you are keen to try then it seems safe to install the "regular" NGK CPR8EA9 as this plug is used on XL700V and NT700V sharing similar cylinder group engine components. Just remember these plugs will live much shorter life than iridium tipped ones SIMR8A9.
The ignition coils used on DN are pretty regular type ones (OEM part 30500MBG003), used on many Honda models, it is pretty sure you do not get any problems with those.
If still the worst happens and you need new ones here is an alternative:
Fuel draining from DN's tanks is complicated, I would try first to use some fuel additive with cleaning features to add to new gas for couple of tank fulls. If the engine runs well there is no real problem in this area, no need to extra cleaning, the fresh gasoline will do the thing in the end.
DN has two fuel tanks: upper plastic with filler neck and lower metallic one. The fuel pump sits in the lower tank ofcourse. Tanks are connected together with rubber hose. It is pretty sure there will not be any problems with the upper plastic tank, it is like a plastic fuel canister, it will not get rusty. I personally have no experience with the lower metallic tank about how it catches rust or not. My bike obviously had sit also for some years with some old gas in it before it was put on running. And when I last summer got the bike it had only 11k km on odo and age was 12 years (produced 2008). The bike was put in traffic in 2011, so it had made about 1400 km per year only, I presume most of the time it was just sitting in garage. And I experience no problems with fuel system.
So I think if yours is starting and running, just use couple of bottles of fuel cleaning additive with fresh gasoline and don't worry.
About spark plug caps. I installed the NGK VD01F as those have 1k Ohm resistor in them against OEM caps (with marking NGK VD05FB on them) having 5k Ohm resistors. As the spark plugs themselves also have 5k Ohm resistors in them it seems for me too much 10k Ohms altogether. I'd like to use caps and plugs with 0 Ohm in them, but it is a bit complicated as NGK does not produce iridium plugs with 0 Ohm nor angled caps with 0 Ohm. The less resistance in caps and plugs the better will be spark and less possibilities for crawling discharges over the plugs/wiring. All this resistance is needed only to suppress radio interference for AM radios, but nowadays this is not a problem as everybody uses FM- or digital radios and for those the spark system is not a source of interference. Too much resistance inline with spark gap will rather cause troubles to your engine.
Please note there is slight difference in angles of VD01F and VD05FB caps, therefore it is needed to route the high tension wires a bit differently. The OEM wires are still usable, no need for new ones. Fortunately they still install copper core HT wires on motorcycles, not the silicon cord crap like on cars.