Hi all I wanted to adjust my idle speed today so took the bike out for a run to get up to temperature before I made any adjustments. From cold start and for the first few miles it ran fine,I went to accelerate past traffic and the bike only fired on 1 cylinder then cut back on 2. I pulled over and the tick over was ok and it would rev ok,I pulled away and it would then intermittently fire on 1-2 cylinders. I have only owned the bike a couple of weeks and have covered 200 miles with no problem. I have checked inside the fuel tank and it is spotless. I left the bike for a couple of hours and once again from cold it was fine but after a few miles it would Miss fire again. Any help much appreciated Regards Rick
Could be sparkplug, plug cap, ht coil breaking down when hot?. In my experience ignition coils that are on their way out fail when hot first. Maybe worth checking the charge rate on the bike when it's hot/ playing up. Same again regulator rectifiers can test fine when cold and fail when hot (overcharging). Would normally boil the battery though and cause poor hot restarting. Water in the fuel is another possiblity but would likely affect cold running as well.
Thanks for the info I have removed spark plugs and both are light tan and set correctly. Is it possible it maybe the TPS ?
Might be worth checking the fuel tank breather. If it's not breathing properly you'd get fuel starvation symptoms after a short while due to a vacuum forming in the tank.
Sounds lean, light tan plugs whilst it has a misfire. A well setup st will have the CO set around 4 to 5%. A bit more than light tan.
If it's completely off a cylinder (drastic loss of power) it will be more than just slighly lean running.
On an injected engine very few things will affect only one cylinder. So either a faulty coil, spark plug, injector or the ECU itself. All the other common problems like fuel pump relay, fuel filter, crank sensor, TPS, temperature sensors, will affect both cylinders. Try to establish which cylinder is affected. Then start by fitting new plugs. If it still does it swap the coils over. Does the misfire change to the other cylinder, if yes it is the coil, if not swap the plug leads and try again. If no change then it looks like an injection problem.
I had a cylinder chiming in and out on my SS. Turned out to be a loose flywheel nut, which allowed the flywheel to float around, taking out a pick-up. I don't think your bike has the same arrangement though.
Thankyou all for your advice,I am off work Thursday and will be trying to find the fault. I will let you know the results. Regards Rick
It's easy to think that this must be an electrical problem but you should also check the valve clearances. An opening clearance that is much too tight combined with a loose closing clearance can result in a valve not closing properly. This may not be noticed when the engine is cold but when it gets hot the opener clearance could close sufficiently to lose enough compression that the cylinder doesn't fire.
