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Discussion Starter · #1 · (Edited)
One of the fettling jobs on my latest bike was to replace the carb rubbers. So, while the airbox was off and the carbs out, I decided to investigate the emissions system that adds fresh air into the exhaust ports.

It's a fairly simple system. There is a drilling through the cam cover all the way down to the exhaust port. Inside the extra little covers on each of the main cam covers is a small metal reed valve set into an aluminium plate. That makes sure that no exhaust gasses find their way back out to the emissions system. Both these covers are linked by pipes to a vacuum controlled valve which connects them to the airbox under certain vacuum conditions. Basically, when the throttle is closed (on overrun for example), fresh air is added to the exhaust and that can cause banging and popping as the unused fuel is burnt in the exhaust.

Now, I've seen posts where people have machined a plate to bolt on instead of the small cover but I didn't have any spare bits of aluminium suitable for the job. I had just enough to enable me to swap this...



for this...



The original gasket fits around the new plate and it all bolts up looking exactly as it did before - but now with the emissions rubbish blanked off.

Job done.

What difference does it make? Who knows. Probably none. I will get around to removing all the hoses and the vacuum valve itself at some point. The free vacuum spigot will give me somewhere to connect the Scottoiler without cutting the petrol tap vacuum line. Removing the emissions hoses and the emissions valve may be a help when it's valve clearance time.
 

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SHW'MAE BUTT
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I thought cooling the exhaust valves would be a good thing had it on my Rangy Rover, why don't you remove the cat box it weighs a tonne which will improve performance.
 

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geriatric
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Basically the pair system works with the overjetting of the carbs and the subchamber in the exhaust to allegedly produce cleaner emissions by allowing air into the exhaust so it contnues burning while travelling and further allowing the subchamber to stay hot inside similar to a catylitic converter.It just suck clean air into the port by the flow of gases from the air filter. I tried blanking it off and found no real improvement in performance.
The only way to really gain any performance or economy is to re-jet and rolling road it. Removing the subchamber will give some weight saving and some ground clearance and a small amount of performance.
I run a 650 africa twin set of pipes and a straight through back box with either a K&N or a pipercross air filter and have gained in performance and got rid of the flat spot found in the 2000 rev range. This elliminates the subchamber and gives a cleaner path for the gases but I found no difference when I either blocked off or left standard the pipework and flow of the pair system.
 

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Discussion Starter · #4 · (Edited)
The overjetting of the carbs has also been sorted at the same time. 125 mains are now in. All other settings are standard. I'm not expecting any performance difference, maybe very slightly better mpg, but considerably less pipework under the airbox :thumbright:

I will consider getting rid of the subchamber by fitting ABP or Arrow headers when I get around to re-greasing all the linkage and swingarm bearings. I'm currently favouring Arrow as the heat shield on the rear pipe can be re-mounted. I suppose I could go for the ABP and get some bosses tacked on as they are £40 cheaper. If it's not quite right after all that, I'll stuff it on a rolling road - although a TKC80 on the rear is not exactly ideal for a dyno.
 

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That'll be the first and last time a TKC80 will be seen on a dyno :D
 

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That'll be the first and last time a TKC80 will be seen on a dyno :D
Nope, three of us went to the dyno a couple of years ago, Fewtrees' AT was wearing a pair of TCKs.

As for the PAIR Alan, nice work! I just bunged 'em up with a couple of wellnuts.
Makes absolutely no difference to the running/performance/economy but it's nice to remove unnecessary clutter ;)

Phil
 

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Now on a BMW R1100RS.
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Nope, three of us went to the dyno a couple of years ago, Fewtrees' AT was wearing a pair of TCKs.
Well there you go! My mistake. :blah5:
I thought the dyno tester would have been picking rubber chunks out of his teeth for the next 4 months. :toothy7:
 

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Discussion Starter · #10 ·
And the verdict having ridden it? No performance difference but it doesn't pop noticeably when throttling off now. Having completely removed the vacuum unit and all the unnecessary hoses and having capped the three spigots (the fourth, the vacuum take-off, is already being used for the Scottoiler), it's much neater under the airbox now.
 

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And the verdict having ridden it? No performance difference but it doesn't pop noticeably when throttling off now. Having completely removed the vacuum unit and all the unnecessary hoses and having capped the three spigots (the fourth, the vacuum take-off, is already being used for the Scottoiler), it's much neater under the airbox now.
Does it make a vast difference to the popping, as that is the only thing that bugs me about mine?
 

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Discussion Starter · #12 ·
Well, there is no popping at all now that I can detect. To be honest, it wasn't offensively bad before though - just occasionally a bit 'fluffy'.
 

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Well, there is no popping at all now that I can detect. To be honest, it wasn't offensively bad before though - just occasionally a bit 'fluffy'.
At least I now know what the cause is.
I sometimes wondered if it meant something was about to fail on the exhaust.
No I have a better Idea I will examine it closer at the next Major service.
 

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Really? I quite like it, to be honest. :D I was wondering if it might be even more noticeable when (okay, "if") I change the silencer. Currently the Fuel Exhausts item looks to be favourite.
I was only worried by it because I had no idea what the cause was.
 

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As long as it is the PAIR System causing the popping and not a wrongly set Valve clearance.
 

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Discussion Starter · #20 ·
Must be about a 400g - not really worth it if all you're after is weight reduction.
 
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