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1977 BMW R80/7 - Part 4
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Roxanne the seventies BMW twin gets a good going over at the hands of Martin Gelder, but all too soon she's back to her old tricks again, stumbling and coughing her way round the block...

The thing with BMWs is that they just keep going. Now I've said that I can expect the engine to fall out of mine next I time I wheel it out of the shed, but by and large they do seem to be well enough put together to keep on going when other bikes might shudder to a halt.

Take my 1977 R80/7, for example. With the charging system sorted and a new set of shocks on the back (see previous write-up), it has slipped comfortably into the role of general runabout and two-up bimbler. It still floats around a bit at speed despite the new rear shocks, and has an odd tendency to weave when moving from the outside lane to the inside lane of a dual carriageway at over 75-80mph, but not when moving from inside lane to outside lane. Odd. Turning the genuine BMW steering damper up to setting No.2 hides the problem but I suspect that a new set of tyres and some careful fettling of the forks and possibly the swinging arm pivots will provide a more permanent cure.

The other niggle that the bike has had since I bought it, and which has gradually got worse with time and miles covered, is a slight hesitation or stumble off idle. Blip the throttle at a standstill and the bike would rev cleanly, but open the throttle slightly to pull away – for example when traffic lights go green after you've filtered your way to the front of a long queue of traffic and need to make a sharp getaway for the sake of politeness - and the engine would invariably cough and threaten to die. I put it down to worn or dirty carburettor gubbins and resolved to give everything a good clean at some point in the future. Eventually. When I get a round tuit.

One thing that can't be put off is regular servicing, and on the air-cooled boxers it's a breeze. The two rocker boxes and the timing cover are each held on with three fasteners. Access to the points would be easier if the front wheel wasn't where it is, but that's made up for by the tappets; how much room do you want?

Yes, I do leave it parked underwater. BMW R80/7 points live behind the advance-retard wotsit
BMW R80 stuff on eBay.co.uk

Eat your hearts out, classic Honda owners... BMW R80/7 tappets, in the breeze

The ignition timing is set by turning the engine over by hand, and checking that the points open as the “S” mark on the flywheel passes the notch on the edge of the inspection hole in the crank case. After years of faffing about with cigarette papers and then light bulbs and crocodile clips, I now use the Radio 4 method. With a handy radio tuned slightly off Radio 4 and the bike's ignition turned on (and the plugs back in the plug caps and resting on the engine), there's an audible “click” from the radio as the points open. Hands turn the engine, eyes watch the flywheel for the “S” mark, ears listen for the click of the points opening. Simple.

And now on Radio Four it's You and Yours, with... BMW R80/7 "S" static timing mark on flywheel

Or not. The engine was firing a long way before the static timing mark and it took three or four attempts before I got the tell-tale click from the radio. I missed quite a bit of Women's Hour because of that. The timing was almost advanced enough for the “F” mark - used to set the timing dynamically at 2,800rm - to be visible through the inspection hole. In technical terms, this is known as “a mile out” and it was a wonder the bike would start or tick over at all.

Attack of the Giant Fingers! BMW R80/7 points, looking a bit sorry for themselves.

The culprit was easy enough to track down; the points were incredibly pitted, a sure sign that the condenser was giving up the ghost. I suspect that as the points had corroded the “point” at which they opened had moved earlier and earlier, shifting the timing of the spark. Cleaning the points' faces meant there was no longer enough movement on the back plate to get the timing close to being correct, so new points and a new condenser were ordered and fitted. At the same time the bike got fresh oil, new air and oil filters, balanced carbs and a set of the platinum plugs recommended by Motoworks when I bought the service kit.

BMW R80/7 air filters, used on the right, new on the left.

What a transformation. The bike now fired up as soon as the button was pressed, seeming to take less than half a revolution to burst into life. Throttle response was much crisper at the bottom end of the rev range, the stumble off idle was gone, and the occasional pinking that I'd noticed at higher revs while under load and after filling up with low octane petrol was a thing of the past. Brilliant.

Except... Over winter, the bike became harder to start, particularly after it had been left un-ridden for a a week or more. If it didn't start straight away – which it rarely managed – the battery would run out of puff while I juggled choke and throttle settings trying to get the thing to fire up. I initially blamed the battery – an expensive Odyssey of unknown age – but experimentation showed that the clock was draining power from the battery while the bike was parked up. With the clock disconnected and the battery doing its job properly, it was obvious that something else was preventing the bike starting as promptly as it should. And that stumble on the throttle was back, but this time slightly higher up the rev range.

I'd had similar symptoms on my old R100S and had ended up replacing both coils and both plug caps, but it's always worth starting with the obvious. Removing the plugs to check the timing showed where the problem lay. Instead of the fat blue sparks I expected, I was getting thin little yellowy whispers. Cleaning the plugs improved things slightly, and switching from the Bosch platinum plugs to ordinary old NGKs brought the bike's running back to where it was immediately after the service.

Resistance is Futile BMW R80/7 spark plugs. The wrong ones....

A posting on the ever-helpful RealClassic Message Board filled in the rest of the picture. I was all set to blame the poncy platinum plugs, but Eagle-eyed L.A.B spotted that I'd been using “resistor” plugs rather than non-resistor ones. That'll teach me to just fit what the shop sends in the service kit, I suppose.

So – for now – all is well again. Starting is first touch of the button again, the bike trickles round town smoothly where before it was lumpy and jerky, and it responds willingly and cleanly to the throttle right through the rev range. I'm even starting to get used to the utterly awful front “brake”....

lub-lub,lub-lub,lub-lub,lub-lub... Tickovver at 800rpm, carbs balanced, and just coming up to lunchtime. All is well with the world...

Footnote: It might seem odd for me to start off by praising the reliability of BMWs and then spend the next 1,000 words pointing out all the problems I've had, but this tale has unfolded over more than 18 months of regular all-weather riding. Roxanne the BMW has never failed to start – eventually – and has always got me where I'm going without needing the toolkit along the way. It's just that when I know something isn't quite perfect, I can't help tinkering...



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