Strange SOBoxer behaviour

This one could be a potential headache for me.

Rode the R100RT into the office today, and got caught up in some really
crappy traffic. I filtered as much as I could, but the R with panniers
is a tad wide so progress was slow.

The engine got hot. Very hot. As in, cooking your feet hot.

As I neared the office, the bike started to splutter and stall when
coming to a halt. Seemed to happen when revs dropped under 2000 rpm.

I put this down to problems with evaporating fuel, parked up and thought
nothing of it.

But on returning to the bike a few hours later, I still had the same
issues, so had to work my way out of London holding the revs at 2000 rpm
whenever I stopped.

After a run on the M4, giving it some revs, it will just about idle, and
revving the nuts off it appeared to almost clear the problem in the
hotel car park.

Tomorrow I have to ride it from M4 J4 to Southall and back, then on
Friday from M4J4 to Hayes and then home in the evening.

Everything seems fine once I'm rolling, and, as I said, it appeared to
be getting better.

Any suggestions? My thoughts are that it appears to be running rich, and
has sooted up the plugs?

What's the odds of it coming to an expensive, oily death half way home?

 

Pull the plugs and take a look at the colour.
Overheating is more often associated with running weak than rich, a weak
mixture is more likely to lead to expensive failures.

 

It pops and bangs on a trailing throttle at the moment, which is why I
suspect right, not poor.

Thinking about it, it has been backfiring a tad on trailing throttle for
a while now.

 

It does sound like it's running lean. Do a plug chop, at varying speeds,
to see whether it's needle settings or main jets.

Two other possibilities: what oil grade are you running? Try a 10/50 or
a 5/50.

Secondly, It does have an oil cooler, right?

 

I'd check for air leaks, too. And pull the carb bowls and check for
gunk in them.

 

At this point I think I should get a man in....

Generic car oil.... As it's what I had in the garage, so not one of the
above.

Yes.

 

Pops & bangs usually mean lean mixture or air leaks downstream of the
throttles. Running hot suggests the same. There isn't a balancer stub
screw that's fallen out is there?

If the throttle's closed then the intake depression is at a maximum so
it would draw more air through a leak at idle or on the overrun, which
might explain the poor idling. A bit of choke might help diagnose that
- if it helps the idle then it's another pointer to a lean mixture.

You can get pops due to exhast leaks at the top of the pipes but I
wouldn't have thought that it would make it run so lean that it ran
hot. Besides that, obviously you'd hear it blowing.

 

SOBoxers are remarkably susceptible to oil grades, especially in hot
weather. I strongly suspect, now, a combination of wrong oil and
carb/mixture gremlins.

 

AND check the carb diaphragms for splits and pinholes, etc.

I know I mentioned this recently (it still hurts!), but one of mine
went, and I had a lot of expensive valve work on that pot as a
consequence: instant lean-ness, hot cylinder, scorched exhaust valve,
seat and guides.

 

Well, they do get very very hot in those conditions. As it is so easy, if
you have a strobe check your ignition timing is spot on.

Clean the float bowls, balance the carbs and do the valve clearances.

But first of all throw the plugs away for some new NGK's.

 

Update.

Flattened the battery trying to start it this morning.... It fired up
and died immediately.

Got the AA out.... He started it, it died. Pulled the plugs. Looking
iffy and very sooty.

He cleaned the plugs and upped the idle speed so it'll hopefully make it
home.

Starting to get tempted to chuck it at the BMW bloke Wessie uses for a
full service, the replace the rattly cans.

Almost tempted to shift it on, as I'm starting to hate it.... Should
have bought a K, I think.

 

Its a Mono yes? good god man it is about as simple and reliable as a bike
can be.

Buy a K? oh just wait until a fuel pressure regulator goes. Or a coil pack.
Or an igniter box overheats. Or the MAF gets touchy. Or the fuel pump clogs.
Or the starter clutch gets iffy. Or a relay goes dodgy.

Nothing on your bike is hard to diagnose or hard to fix. I didn't mention CV
carb diaphragms, had a recollection you had the carbs overhauled? maybe that
was FJ. Two minute job to check them. I always keep a fresh set of plugs
under the seat BTW.

Yopu have replaced the original coil pack with the new uprated twin output
sealed lead one I trust, hmmm? That's always a likely culprit until you do.

Perhaps a nice single speed bicycle would be safer.

 

Yes, it's a Mono. May be simple, but not as reliable as a Honda.

Oh.... Not good.

It's a CBA thing with me - I want a bike that 'just works' like my VFR
did - it never needed anything other than oil and filter changes.

No.

Looks like I really need to get the BoL out and order some bits from
Motobins / Motorworks.

 

Sooty? well, that's my guesses down the pan, then. Dry sooty or oily
sooty?

 

Dry sooty.

 

Bollocks is it not.

All that ever goes wrong with my boxer is fork seals, and I put that
down to ham-fisted landings rather than any form of manufacturers
failing. And my pet BMW chap's due to drop off a new pair in a couple of
days.

 

Check the coil.
Check the coil.

The cracks are in around the ht outlets. Can be hard to see.

 

Those things are eye-wateringly expensive. As are OEM HT leads.

This is my first, and last, BMW.

 

Try the electronic ignition black box under the tank, attached to a heat
sink.

If the heat sink paste has gone "off" it can reduce the heat transfer and
bugger the black box.

It was one of the things I tried when my R80 Mono recently gave probs. I got
a new replacement black box from ebay for a tenner, apparently they're the
same as fitted to a multitude of Bosch equipped cars of the late 80's and
early 90's .... the replacement worked BUT caused my rev counter to misread
below 2000 rpm (it would read double the actual revs below a real 2K) ....
heat sink paste is easily available at most PC shops.




--
Steve Parry
BMW R80RS, 03 BMW R1100S Boxercup, 07 K1200GT SE
02 Suzuki DRZ400S, 87 Yamaha FS1, Sukida SK90PY, 91 Kawasaki AR50,

www.gwynfryn.co.uk

 

Cheers.

Stuff I've looked at, anyway:

Carbs. Can't see any issues. Diaphragms are fine, and I've blasted
everything with carb cleaner.

Battery. Fecked. Seems to charge, but is down on voltage - drops right
down to the bottom of the gauge when you thumb the starter. Will order a
new one.

Plugs. Bosch Super 4s fitted - I had them kicking around. Might not be
the right ones, though..... will order the correct ones. (Although these
did improve matters a bit!)

HT leads. Old. Will replace.

Coil pack. Not checked yet. Good used one sourced and ordered for fault
finding purposes.

Ignition module. Golf module sourced on ebay.

Hopefully everything will be here in time to have a play on Saturday.