Bike only runs on rear cylinder, sometimes front kick in. Replaced and double checked all electrical parts including ECU so I am looking at fuel. My question is simple. If my valve clearances were out or there was some other non-timing issue in there (already checked) could I get no or little fuel if I have good compression?
Maybe worth checking the input lead to front coil, I had a nick in the insulation in mine which caused months of poor running. The nick in the insulation was about 2mm from where the wire enters the connector and was really difficult to find, this had allowed water to get in and corrode the wire.
I agree - treble-check electrical parts. But fuel is a valid next step. I can't tell from the post whether you have carbs? More to go wrong with them than with fuel injection I'd say. If you have good compression and valve timing is correct then it's extremely unlikely to be a valve clearance problem - thinking about 4-stroke petrol engines in general, if compression is good (should obviously be similar for the two cylinders if you are actually testing/measuring) then that implies that piston/rings are good as well as valves sealing onto their seats. If valves have a clearance far too tight (which would imply actually partly open when they should be shut) then I'd expect compression to be weak. If clearance is too large, they'd have to be amazingly loose (with Ducati that would imply something broken) to cause a major misfire and would beterribly rattly too.
This is your ST4s? As said, quickest way to check if valve clearance closed up is a compression check. A common occurence on 2 valve engine but as also said, less likely on yours as they are more likely to get sloppy/too much clearance first (could still affect running of course).
Cheers Matt, Checked and changed the connections, Went a fair way down but I shall check all the way to the loom its Injection, I can go back to electrics again. Can't here much rattle other than the clutch Changed the CPS and gapped it Yep ST4s, I shall taker a look Cheers Guys
Imho, can't see anything mechanical allowing the front cylinder to chime in occasionally. Only electrical faults behave like that... Presumably you replaced plugs and leads as well...
I had an S4 Monster with intermittent horizontal cylinder misfire. It was the actual plug cap had a crack in it and was shorting to the head instead of firing the plug. It only missed at low RPM thrashing it ran fine
When it's running on the one cylinder if you pull the non running cylinders plug lead off and hovver it over the spark plug can you hear the spark jumping the gap ? If yes , can you probe the injector plug with a bulb type text light make sure there is battery volts on one side of the two pin plug , then swap test light croc clip onto battery positive a test for earth pulse on the other wire .....if all this checks out good suspect bad injector , you could swap injectors around and see if missfire transfers onto other cylinder .....you may of done all this already , you haven't said
Spark jumps and I also have one of those chamber links where you can see the spark. I wired up LED's to the injectors and the coil LT leads. Injectors were swapped too.
