Holy thread revival! It's only taken me two and a half years but I've finally got back onto trying to sort this bike! Bought myself an ultrasonic cleaner and cleaned and rebuilt the carbs over the weekend. I had two sets of carbs so I hand picked the best bits to make up the best I could and completed the fit up with fresh gaskets and float valves. Battery is on charge now so once I'm back from the MotoGP I'll pop some fresh fuel in and see if she runs... Not sure what the grand plan is, wouldn't need much more for an MOT so in two minds as to whether to use her as she is, sell her on or go for a full restoration. Time will tell. In other news the GSXR departed today and will be replaced with something yellow from Bologna! Excited doesn't cover it.
Back at it! Got the battery into the bike today and turned it over to check for spark, excellent on the front cylinder, nothing on the rear. Swapped coils and CDIs, still only sparking on the front. Checked all the resistances and it appears to be the pick-up coil for the rear cylinder so I'll get a pair ordered up. Strangely one of the plug caps was also showing high resistance but didn't seem to affect the quality of the spark...
When this happened to my SS, it turned out to be a loose alternator nut that allowed the flywheel to wobble and take out the pick up. I'm told that's not necessarily common though
Wow, that's worrying, that should be torqued up high and has a dished washer behind it too for pressure.
When I got the SS, I was warned about two potential problems to watch for. One was cracks near the headstock, the other was the alternator nut. Both happened.
Cheers guys, definitely getting some new coils once I get the bike running. Just don’t want to commit to too many parts until I know what I’m working with. Thinking about it now the bad cap was on the front cylinder which had been causing me problems before I took the bike off the road, might have been the issue all along.
Small update. New pick ups fitted (what a pain in the arse setting the gaps), alternator cover back on, oil topped up and new caps fitted. Time to check for spark...NOPE battery has gone dead and I mean 0V dead. Stuck the battery on charge for the day whilst I did a couple of jobs on the 748 and the mountain bike. Deep joy, we have 12.5V! Battery fitted, do we have spark? Hell yeah and hell yeah. Tank back on a few litres of fuel added and...it runs!! Only on one cylinder, at 3000rpm, with the occasional backfire but it runs! Super chuffed that there’s a bit of life in the old girl. It’s the horizontal cylinder that’s not firing now (before I stripped the bike the issue was the front cylinder). It’s definitley getting spark and fuel (I got a face full when checking the spark). Carb mixture set to 2.5 turns out on both. Bike is back in the garage, hooked up to the charger and I’ll get back to the fault finding in a day or two. Any pointers greatly appreciated!
I would check the polarity of the coils, very easy to wire back to front and itll run but very rough. If its getting fuel and a spark it doesnt necessarily mean the spark is at the right time. Try swapping the coil wires round on that cylinder
Cheers, I’ll check that out. Are you thinking that the issue could be with the pick up coils or the main coils?
This sounds wrong. Was the fuelling definitely sorted? - Could the carb for the front cyl be flooding / overfuelling and killing the spark?
I had the same kind of problem trying to get my 525 supermoto to run without it pissing fuel everywhere and not ticking over no matter how many times i set it up or stripped the carb down....i conceded and handed it over to the local KTM specialist (Unity Road Motorcycles). 150 quid later it was ticking over smoothly and i was handed back a handful of worn carb parts that to me looked totally fine....its been fine since (that was 2 years ago from recollection).
Sorry I see what I’ve done there, the issue was horizontal, but is now vertical. Fuel was a mist rather than a spray so don’t think it’s too excessive. Will check the electrics and see where I go from there.
Had another bash last night, started very easily on half choke and idled at about 2500rpm but again, only on the horizontal cylinder, nothing on the vertical! Left the bike to warm up, gradually reducing the amount of choke to nothing, was struggling to idle so upped this a little and left it running. When I had it at a normal(ish) idle there was the occasional back fire as if the vertical cylinder was trying to catch but it never did. Stopped the bike and pulled the plug and it wasn't wet, gave it a clean and stuck it back in and restarted the bike. Still firing on one only. Blipped the throttle a few times and the revs seemed to be hanging a little so I backed the fuel screws out half a turn. This seemed to improve behaviour but still nothing on the vertical cylinder. Took the bike for a spin around the block hoping that a bit of load and engine speed might spur it on, not joy. Running out of ideas now, have looked down the carbs and the butterflies both appear to be set in the same position (both just exposing one of the tiny bores on the inside of the carb) so I don't think it's a sync issue, both slides seem to be operating as intended when the bike is revved. Could it be a choke issue or a float height issue? When I overhauled the carbs I stripped and cleaned everything in the ultrasonic bath and blew through with compressed air, float needles are brand new and all jets were thoroughly checked before refitting. I'll recheck all the wiring again and try moving ignition components around to see if the problem moves. Answers on a postcard!
There is plenty of info on the carbs on carbed SSs on this forum......I have posted it quite a few times, some fairly recently. The pilot circuit controls the engine up to about 2500rpm, then the slides start to open and the main jet takes over. The pilot circuit can be easily blocked. The fuel level is actually a matter of guesswork / trial and error if you don't have access to diagnostic equipment.
Cheers I’ll have a look over everything again and try running and ignore no joy I’ll restrip the carbs. It’s the running on one cylinder that’s baffling me most. Will set aside some time to delve deep into the forum for carb tuning info.
