Glowing Exhaust Downpipes

Hi

A couple of months ago, whilst testing that a replacement radiator/fan was working correctly, I noticed that when my CB500 is up to operating temperature and revving >5K revs (on the centre stand in neutral) then the exhaust downpipes glow red-hot. When closing the throttle back to tickover they then cool down and no longer glow.  

When I purchased the bike, the previous owner told me that at some point it had replacement stainless downpipes fitted (they were considerably shinier and newer than everything else on the bike). The factory silencer was still fitted at this point. 

I have done 3K miles since noticing the glowing downpipes without issue (I depend on it to get to work, never saw it when the bike had been out on the road, and didn't have a chance to investigate properly). 

I recently acquired a second-hand Fuel silencer, and figured that before I fitted that it would be wise to re-jet, thinking that a lean mixture may have accounted for the glowing downpipes, and an aftermarket can could just worsen it (+ melt the plugs, destroy valves etc.). 

I then fitted a Dynojet kit containing, amongst other things, a 124 main jet size (stock is 122). A link to the Dynojet instructions/specifications is here http://www.dynojet.com/pdf/European/Honda/E1160.001.pdf . The carbs were a bit grim - there was some muck in the bottom of one of the float bowls, which I cleaned out, but on inspection the air filter was also in pretty bad condition. I haven't yet replaced it - ideally would like to fit a K&N but would like to suss the glowing downpipes first before I make the mixture even leaner. 

With the Dynojet kit and the Fuel silencer fitted, I have checked the downpipes again and they STILL glow red hot: 



 Apart from this the bike runs great and shows no other symptoms of incorrect mixture or any other woes, other than a small amount of splutter/backfire on overrun. 

To summarise... My question is: 

What are the plugs like?
It may be that the downpipes are made of a thinner gauge tube than standard and conducting heat faster, weird one!

Plugs looked ok last time I checked (after I saw the glowing downpipes but before I re-jetted and fitted the aftermarket can). I will check again! Good excuse to have a good hard ride before taking a reading 

Agreed - it is a weird one! Shame the receipts that came with the bike don't shed any light on the downpipes' manufacturer!

I just checked mine and they look the same in the pitch black garage.Fitted a Fuel can with baffle in, Motad stainless downpipes. I never checked before with the stock downpipes/can. 

I believe that the main jet you changed only comes into effect at roughly 3/4 to full throttle openings so perhaps the other jets are lean. Or maybe they all do this and you are the first to notice.

HomeBrew wrote:I just checked mine and they look the same in the pitch black garage.Fitted a Fuel can with baffle in, Motad stainless downpipes. I never checked before with the stock downpipes/can. 

I believe that the main jet you changed only comes into effect at roughly 3/4 to full throttle openings so perhaps the other jets are lean. Or maybe they all do this and you are the first to notice.

Thanks for checking!! Is your mixture bang on? 

The Dynojet kit also included a replacement needle so it shouldn't be running lean at mid-range throttle.  

Hopefully they all do this and it's nothing to worry about    thought it was worth checking though!

I don't know about the mixture- a experienced mechanic said it was a bit rich when I had the stock exhaust system, stock filter. Now its got a "Hi-Flo filtro" air filter and upgraded exhaust, so may have changed. I'm going to put the expensive stock air filter back in. 

If the bike was moving the air would cool the pipes a bit. It would be interesting to hear what other peoples bikes do.

I know this is no help at all but i once had a Wankel engined DKW and it's exhaust pipes did that.  But Wankels were known to run hot !!

That happened on my bike at 95k. The original headers it was wearing were rotten and I wasn't surprised when, a few weeks later, the headers actually sheared off. I had a spare set anyway.

It could be that your engine's running hot, but it's most likely thinner gauge steel, as has been said.

stevew wrote:I know this is no help at all but i once had a Wankel engined DKW and it's exhaust pipes did that.  But Wankels were known to run hot !!

I recently read an article on rotary's and the general consensus was that the DKW was the best of the bunch. It went on to say that it could have been a great machine with a little development, but Deek pulled the plug.

badseeds wrote:That happened on my bike at 95k. The original headers it was wearing were rotten and I wasn't surprised when, a few weeks later, the headers actually sheared off. I had a spare set anyway.

I could be that your engine's running hot, but it's most likely thinner gauge steel, as has been said.

Hmm - mine has only done 36K total and I reckon 20K at most with the new headers, judging by their condition. Assuming that the headers are just thin stainless, as suggested, I'm hoping they should last some miles yet! 

Will still check the plugs for any signs of running lean after a good thrashing and report back! 

Thanks!

badseeds wrote:

stevew wrote:I know this is no help at all but i once had a Wankel engined DKW and it's exhaust pipes did that.  But Wankels were known to run hot !!

I recently read an article on rotary's and the general consensus was that the DKW was the best of the bunch. It went on to say that it could have been a great machine with a little development, but Deek pulled the plug.

Always wanted to try a car or bike with a Wankel in it - a friend had one of the Nortons from the 80s but I never got a chance to have a go!

AAFord wrote:
Always wanted to try a car or bike with a Wankel in it - a friend had one of the Nortons from the 80s but I never got a chance to have a go!

Wow! Yeah I'd be annoyed, too!