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  #1  
Old 17 Dec 2010
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Glowing exhaust pipes on an airhead

I have a '78 R100 RS Motosport. I've had it for several years but for the last 4 it's been mothballed in France.
I'm intending to start using it again this year but it has always had a fault I've never got to the bottom of.
It seems to run fine but if left ticking over while stationary for more than a few minutes the exhaust pipes start to glow. Just a dull red at first but then soon turn to cherry red.
I've checked the timing (several times). The plugs show no sign of running too hot. It pulls cleanly all through the rev range and as soon as I start moving they cool down.
But something's not right.
The only non-standard thing about it is that the pipes are stainless. Could it be they are thinner than normal? Does unleaded run hotter than the 4* the engine was designed for?
Any ideas please?
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Old 18 Dec 2010
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stainless pipes are usually thinner walled or single walled..... they may get hotter, I dunno I never had any stainless pipes on my Beemer, but as u have had it in storage there may be a chance that there is an air-leak between the carb and the carb boot.... this could make it run lean thereby making it run hotter, though you say it does not appear to be hot. also it is Air cooled, they really don't do well just idling away and not being run, in the workshops we always used to use a fan in front of airheads to keep em cool if we had to run them up for more than a minute or so........ just a thought..

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Old 18 Dec 2010
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Stainless not a good conductor

As the title says S/S does not transmit heat quickly, a fan is good advise. After all, it is an Airhead.

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Old 18 Dec 2010
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Hi Harleyrider I have stainless pipes on the Bilgepump and they never get that hot, something seems wrong. As you seem to have eliminated everything on the ignition system and your sure the carb's are fine it must be the exhaust valves sticking a bit, stretched or cracked or the seats worn allowing gases to burn into the exhaust ?. The valves are prone to stretching and parting company with the heads at mileage as low as 60 thousand plus miles. Jake.

Last edited by adventure950; 18 Dec 2010 at 12:59.
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Old 18 Dec 2010
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Quote:
Originally Posted by harleyrider View Post
I have a '78 R100 RS Motosport. I've had it for several years but for the last 4 it's been mothballed in France.
I'm intending to start using it again this year but it has always had a fault I've never got to the bottom of.
It seems to run fine but if left ticking over while stationary for more than a few minutes the exhaust pipes start to glow. Just a dull red at first but then soon turn to cherry red.
I've checked the timing (several times). The plugs show no sign of running too hot. It pulls cleanly all through the rev range and as soon as I start moving they cool down.
But something's not right.
The only non-standard thing about it is that the pipes are stainless. Could it be they are thinner than normal? Does unleaded run hotter than the 4* the engine was designed for?
Any ideas please?
Oh but it is

That is exactly what happens

Nothing to worry about. As soon as you start driving so that you get some wind on the down-pipes they should stop glowing. If that is what happens - all is well

s/s pipes glows less than the original steel pipes.
RS 1000cc from late 70:ties glowed the most. You do have the 40mm down-pipes, right?
Later 1000cc RS models with 38mm down-pipes does not glow as instensly, they only turn sort of orange-/red:ish. 800cc and less cc should never glow.
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Old 18 Dec 2010
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That's interesting Albert I had an 100rs back in the 70s the pipes I recall were really blackened and it had heat shields down over the front downpipes - must have been the reason why but I never recall them getting orange or cherry red mind you I was younger and just rode the thing never really took much notice of stuff - I suppose you don't when your in your teens. Is it just the rs and s models or do most of the 1000 get the same. ?
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Old 18 Dec 2010
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This is my 2nd RS. My first 1 was also a '77 model which I owned in the early 80s. I used it for despatch riding and did over 200,000 miles on it in 2 years. I'm sure that didn't have glowing exhausts. Hence my thoughts the cause could be either the stainless pipes or unleaded petrol. I'm not sure what size pipes they are and I'm not with the bike at the moment to measure it.
I realise it's not good practise to leave a bike ticking over in the workshop for long but I don't expect the pipes to start glowing while I'm sitting at traffic lights. This isn't a new problem after it's been stood for a while. This is something that was happening all the time in the 2 years I rode the bike before it went into storage.
Thanks for all your replies. I'm tempted to find some standard pipes for it and see if that cures it, but I'm also wondering if I should be making some adjustment to the timing for unleaded fuel.
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Old 19 Dec 2010
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...not a controversy again...

Guys.
RS 40mm down-pips are known to glow when driving in traffic jam, especially on warm -dry- summernights.
There is no way you can expect to see this in day-light.

As with all things in the world - it is not an absolut truth. There were those who did not have glowing down-pipes when subjected to longer periods of idling, and that was considered "weird" back then.

Yes - 1000cc are prone to get the down-pipes glowing. RS 70hp from the 70:ties did simply glow the most.
Undressed beemers do not have glowing down-pipes in corresponding frequency. It -might- thus have something to do with cooling of the whole engine.


As for not seeing that they glow... hardly where once attension should be focused in traffic-jam, at redlights, etc...

If you still are worried - install two pip-fans so that you can get some "wind" on the barrels at idle; my mechanic have done so on his side-rig after he noticed his red down-pipes (after driving some 40 years and >>>1 000 000 miles...).
He has a 90A Bosch alternator installed so there is plenty of electricity to drive his fans - on a stock 280W there is -no- extra ampères at idle for any extra equippment incl drivinglights...

What I have on my primary beemer, that I do think interfer with the glowing, are:
- deeper oilpan / spacer
- oil-cooler
- belt and pulley driven car alternator
- dual ignition
- s/s exhaust system
The last beemer I aquired, R100RT 1981, does have glowing down-pipes when driving down-town in traffic jam with way too much idling. Hence my guess is that dual-ignition and improved oil-cooling does play a significant role in lowering the temperature of the exhaust fume so much that it is hard to get the down-pipes glowing; and the strong fan on the Bosch 70A alternator (older external version) do also matter I guess.

Just except the fact that most 1000cc down-pipes are prone to glow. RS pre nicasil barrels (pre -81) are more so than other 1000cc's. One -can- get both 800cc and 750cc down-pipes to glow as well, when one tries hard enough (not adviceable!).
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Last edited by dc lindberg; 19 Dec 2010 at 15:24.
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Old 19 Dec 2010
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Thank you Albert. You've put my mind at rest. I'm not going to worry about it anymore.
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