Greetings all!

Long time reader, first time poster. The wealth of knowledge on here has already helped me bring my barely running '89 900SS to the state that I can take it out and enjoy it. But there are a few bugs I still need to sort out.

I guess I'll start with how I got my bike. A family friend had it as part of his collection which he originally got for his son to tidy up/work on but as so often the case with old bikes they both lost interest and it ended up becoming an aesthetic piece. I had expressed some interest in getting hold of a cheap older sports bike that I could tinker with. Fast forward past a few pictures sent to me and a bit of back and forth on what was wrong/price/etc and I was heading down to his farm to check it out. Even among the company it kept in that massive shed it still stood out and without ever turning it over (dead battery) or kicking a leg over we had negotiated on a price and it was mine.

A new battery with the largest CCA we could find got it running, but it clearly didn't like being started. Starting was a 5-7 minute ordeal with me questioning why on earth I decided to leave the safe reliable world of modern Japanese supersports and buy an old Duke. I eventually learnt her secrets and was able to get her started somewhat reliably in a bizarre sequence that also caused the rains to come.

Enough back story, cue me finding this site and the following fixes/mods!
Motolectric starter upgrade wiring - fixed my starting worries big time, not quite 'japanese' quick but I no longer feared that anything less than a freshly charged battery meant I wouldn't ride that day, would still have to do a rain dance with the choke and throttle if it was cold out though. Also cleaning and re-grounding fixed my battery drain issue.
Dynatek DC10-1 coils, Magnecor KV85 wires, new NGK plugs - I did these all at once and had a aluminum bracket made up to fit the dynatek coils, WOW! What a difference, first time starting and I swear before my thumb had reached the bottom it had started and was idling smoothly.
The other little things are - New fork tubes and rebuilt front forks, new indicators, good used indicator switchblock to replace my broken one, brand new rear caliper, rebuilt rear master cylinder, new sprockets and chain, new tyres, and assorted fluids and filters replaced.

I now am comfortable taking it out on rides but there are still a few things my googling, this amazing forum and assorted factory manuals haven't been able to help me diagnose/fix.

Problem 1: At a little lower than half a tank she coughs and splutters whenever you give her a bit of 'go' with the low fuel warning light flicking on and off. At normal steady throttle shes fine, but soon as you pull back on the throttle it's just like I'm running out of gas. First time this happened I figured "I need to get to a fuel station quick!" and thought nothing of it. Only after about 3-4 tanks of this I've realised I'm only putting about 10-11 litres of petrol in. I believe I might have something in the fuel line but thought I'd throw it out here to see if anyone has any ideas. She does run perfect with a full tank of gas, it's only once it drops to about 6-8 litres left that it acts like its running out of fuel.

Problem 2: Sporadic "clunk, clunk, clunk, clunk" when coming to a stop. This sound exactly like the chain is misaligned, but it does it only so often, not related to front or rear brake, and as far as I can measure, my rear wheel and chain geometry is goods. Alignment marks are even left to right, and my socket and wooden ruler didn't show a noticeable misalignment of the chain. Could be too loose? I measure it at around 2.5cm-2.8cm for slack.

In case it's somehow related my clutch slave is well on its way (squeak, squeak, squeak) and a replacement has been ordered and I should get it fitted next week sometime.

Thanks for reading and hopefully someone can help me diagnose the problems I've got so I can enjoy her more fully!

Hopefully I didn't bore you with a wall of text so I've attached some pictures.

I would check that the fuel pump is working , like check for pressurised fuel leaving the pump ... don't just listen to hear it working ( if its electric ) and if its a vacuum diaphragm pump ( ah la monster ) check vacuum hose . Sounds like its relying on gravity to get fuel to flow and when tank is 1/2 empty fuel level in tank drops below fuel level in carb .
Does the clunk clunk happen in all gears ?.........chain not hitting on the centre stand ? or top of swing arm ? all chain rubbing blocks/ guides all present ? Probly pay to check that the rear sprocket is tight and the carrier bearing is OK
There is a clutch slave mod in the FAQ's using a later model slave piston assy , if your in the area its probly a good move
Bike looks good.

Welcome to the forum. That's a clean looking 900SS. I like the bracket for the coils, too.
I assume you replaced the belts before starting the bike although that isn't mentioned. As for the ignition upgrades; as mentioned so often on this forum do still check the voltage at the coils. If there's (still) a voltage drop your upgardes won't be working at their full potential yet.

Your fuel problems sound like gravity feed to me as well but that can`t really be as the fuel pump is electric and inside the tank pumping the fuel upwards. (Unless the connection between pump and filter or filter and in-tank tubes are interrupted). Do check if it works and produces fuel pressure properly after draining half the tank. Check the fuel pumps' mesh filter and replace the fuel filter. Then check the fuel hoses for leaks and tight fit and that they are the correct ones for "in tank" use. If the bike was laid up for a longer while did you empty, flush and inspect the inside of the tank?
Are the hoses for tank breather and fuel return connected correctly or swapped?

Regarding the noise. Is the sprocket carrier sitting tight, are all sprocket carrier bolts and the sprocket nuts tight and is the conical spacer there and installed correctly with it`s wider side towards the swingarm?

The wsm mentions a chain slack of 15-20mm with a rider in the saddle.
If you ever remove the rear shock you can try. Lift the rear wheel until the wheel axle, swingarm pivot and drive shaft are in one straight line. In this position the drive shaft and wheel axle are the farthest apart. Adjust the chain so there is no slack (but there shouldn`t be tension either). If you then reinstall the shock you can measure the chain tension and will get the correct value. You can also measure the values with the bike on the center stand or someone sitting on it as future reference. Doing all this is unnecessary tho (unless you do modifications or a swingarm swap) as it will only confirm the factory values.

Hi mate i have the 89 900 as well, with magnetti ignition and interested in the dynatech coils, looking on ebay and they seem reasonably priced are all the DC10-1 COILS the same as some are advertised for certain models of bike , also do your coils bolt in the original bracket holes, sweet bike mate ,enjoy

Thanks for that, i'd hate to purchase wrong ones and have the hasle of sending back and all
that, the dyna coils seem to get some good feedback

Yes, certainly check the fuel pump function. One of those spigots on the tank is the return, one is the vent, and one is the tap from the pump. If the pump is not connected, or the hose is rotted away, you will only get about half a tank of mileage. You can not run that bike without a pump. If you haven't yet, replace those fuel lines in the tank. Mine were pretty ugly. The old hoses weren't meant for the additives that are in modern fuels. And use clamps intended for fuel injection hose, as they clamp more securely.

As far as that clunking noise when slowing down or a crawling speed, my 750 does the same thing. Never figured it out. Its something in the transmission, and has done it for years. I think one of the dogs is trying to engage, and just floating around.

Cheers, Phil

If you have a Kokusan ignition (2 blackboxes) they will work. It doesn`t matter what bike the coils are for or from as long as they have 3-5 ohms primary resistance .