I finally got around to stripping down my 749R to investigate its misfire. One thing I had noticed was a small build-up of oil where the vertical cylinder meets the crankcase, at the back, so started there. Turns out to be a fair bit of oil in the vertical cylinder plug well, so… - may this have been the cause of the misfire? - the plug was covered in oil when I removed it, but as it appeared to be clean, I'm assuming/hoping that it wasn't in the combustion chamber and the plug just got covered as I removed it. - I'm therefore guessing that its the head cover gasket that's leaking. Any other suggestions? - I might as well replace the plugs while I'm at it - Champion RG59V - but see hugely varying prices online for these - from £2.50 to £20. Are all RG59Vs the same? Thanks…
It's pretty common to get the plug wet with oil. The gaskets aren't good, even when new. I bed them down on threebond, new or used. Can cause misfires and could well be you're problem. Pull the rubber off the coil stock, catch the spring and give it all a good clean. Can't tell if it's good until you try it TBH, but cleaning first is a good start. Yes, prices vary wildly on the surface discharge plugs. All the same though.
Thanks for that - you reckon it's more likely to be the big gasket rather than the o-ring below? I managed to get a mouthful (don't ask) and it tasted rather soapy but not like sweet coolant (yeah, I've done that too) - think it's 300v.
Yeah, 1215 is just the ticket. I do both the gaskets. Large perimeter one and the round one around the plug recess.
Thanks Neil - did the deed today (took me a couple of hours with cocktail sticks to remove the silicone sealant previously applied though). One thing though: workshop manual seems to suggest that rocker cover bolts should be tightened in two stages - first to 10Nm, second to 22.5Nm. That seems bloody excessive for rubber compression washers on a magnesium cover that isn't under stress. Am I reading the right thing?
Think it's just 10nm. The cam housings go down in two stages, but no need to tighten the cover screws that tight...think you'd be snapping them. They're only M6
Fortunately, I got to 10Nm and decided that that was quite enough! Left it to cure, put new plugs in and bingo! Two problems sorted in one: I'd only decided to sort out the oil leak whilst pondering the cause of the long-term misfire, only to find that they were the same thing - the oil leaking into the plug well shorting things out. That was a nice cheap cure Took the bike out briefly today on private roads (pending a new MoT) and it's pulling like a proverbial: 749R+57mm full Termi+Moto Rapido remap and the fuelling is just perfect. Just need to put a bigger rear sprocket on now and fine-tune the suspension!
Thanks - the terminology in the manual was ambiguous and I did think it might refer to the cam housings - a two stage tighten seemed OTT for a valve cover…
