Hi Milkman
I have been following your post for a while and it seems sort of reminiscent of things that were wrong with mine.
This intermittent misfire may well still be carburettor related but I don't know anything about them so I will stay off that. EXCEPT that I hope you did not use high pressure compressed air when cleaning your carbies. That's a no-no - it just pushes dirt further in. I learned THAT the hard way!
You state your problem arises when hot. Electrical resistance increases with heat. Resistance causes problems ... Hmmm Sounds electrical.
The Haymes manual has a pretty good diagnostic page which I very cleverly ignored for two years ... DO IT by the book. If you don't have it I can 'lend' it to you.
Buy yourself a pocket multimeter from Jaycar or AutoPro.
Haymes manual states 4 causes of problems - in order
HAYMES
a) faulty spark plugs, supressor caps and HT leads
Replace them all. (I think you have)
I use Bosch plugs and those 'off the rack' blue leads you get at any AutoPro store ( the blue matches the BM logo) They are very reliable. Ugly but reliable.
HAYMES
b) Loose, broken, or corroded connections or damaged wiring.
OK so you say you have gone over the wiring ... yeah, that's what I said!
Old wiring (and that's what we are dealing with) need not be 'corroded' in the sense of showing greenish build-up or dirt. The surface of connectors over time builds up an invisible, microscopic layer of ENAMEL causing poor connection and resistance. This must be removed from ALL connections, inside and out. Grind down the end of a flat needle file to the size of a spade connector. You can buy them at the local hardware. Pic attached.
Use it to file out the female connections as well as cleaning up the male spades. Then use CRC Automotive Electronics Cleaner (Code 5013) (this one won't eat your plastics). Pay particular attention to the orange connector plug under the alternator cover (from the bean can to the main loom). It gets overlooked. FILE all connectors aggressively (within reason).
NEXT pay attention to your earth points which is where any brown wire reaches the frame. File off all the surfaces. Clean the bolts etc with a wire brush.
NEXT do your fuses and fuse block.
NEXT check your battery connections to the frame, loom, gearbox and battery itself. File off the enamel. It will be there.
NEXT remove your ignition main switch. Clean the outside connections as above if you haven't already done so. Using the CRC Electronics cleaner, FLOOD the inside of the switch and turn it aggressively and repeatedly back and forth through its entire range. Do this 10 or 12 times until the fluid going in runs out clear. You will be surprised at the crap that comes out. Repeatedly actioning the switch will help clean the contacts inside which will also be enamelled. If it falls apart, and it might, you will have found your problem.
NEXT This gets a bit tricky. Find any connections in the loom that have been soldered. Soldered connections in motorcycle looms crack due to vibration and do not create very good connections. Remove the solder and reconnect with crimp fittings. The tricky bit is deciding what BMW soldered - such as the diode board. So only look at the general 'outside' wiring loom. If in doubt leave it out.
HAYMES
c) Wear or damage to the advance mechanism
I had no reason to do this and haven't ever. There are other posts on how to do it. I WOULD do it in this case, but only if the problem persisted after the above 'loom clean'
HAYMES
d) Faulty electrical components.
It's not the coil, you know that and the sensors rarely fail. Beyond my expertise (or lack of it)
NEXT put it back together and see how it goes.
I did my bike twice before I fixed 'something', but I suspect that it was corrosion/enamel build up in the orange plug under the alternator cover.
My friend had to do this process three times to his Guzzi before it worked for him. But it did.
My R65 went from going "OK for an old BMW' to 'bloody fantastic, can't believe the difference'.
Takes 4 hours and 4 cans. Or 2 hours and 1 can etc.
PS My instrument mounting bracket was rusted too but came up remarkably well by removing all the paint and respraying. I thought it was a bin job.
PPS Use only Premium Unleaded.
If you use the same petrol station all the time and have trouble, try another one. For instance Ducatis misfire on United. Old Triumph twins run like crap on BP. In fact, don't use BP.
Good luck
I'm in Melbourne if you want to ring. 5967 3218
And for a test ride ... there's the Southern Classic races at Broadford Saturday and Sunday.
