Back to BM's yet again...:) And carb question...

Wrigsby1 said:
There's no balance pipe and now I see what you mean about the Y piece... It runs back on itself...! Looks a shite design and seen as the gasses a trying to get out, the LH pipe is going to have a far more difficult job than the straight piece RH...:confused:I've measure the header pipes and they are 38mm dia...PS I know its cracked at the join (top and bottom...:cool:) ) and I need to sort the hole for the emissions thing that the PO -2 removed... I was looking at it the other night and the 3 layers gaffa is a temporary job...
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More of a t piece than a y. If you look at the boxer supplies website that have a good range of y pieces though mostly for gs machines.For a few quid more than the keihin you can get this one http://www.bmwboxersupplies.com/images/100r.JPG to be honest if you can find an original 100r collector and downpipes it's well worth giving it a go to see what the starting point is.
 
And this on ebay looks like it should flow ok although that weld looks a bit lumpy. That boxersupplies one Rob pointed to looks good. I know that the wisdom is that the collector box tunes better but I would like the R100Gs to have a sound more akin to the thump thump of a KTM even if it sacrificed a ( very, very)very small bit of performance.
 

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solidstate100 said:
If you run the system with a y piece and not the collector box you may well find that the baffles in the oem exhaust get knocked out (and another tuning headache can be casued...)
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Was wonder the very same thing... Had similar on a k many years ago when it was running the leaner end of the scale...
 
I have a Keihin on my R100 GS and it works just fine.

But IMHO it needs a less restrictive muffler and airbox.

There can also be a problem with aluminum gaskets between the various parts of the exhaust system - some can end up partially obstructing the muffler inlet, and the large GS collector copes with this better than any Y piece.
Once you have discovered a way to remove what can become a molten blob of metal you will have probably solved the problem of the less restrictive muffler too, and you will be doubly rewarded with a pleasing change in exhaust note and increased throttle response across the rev range, something which is not always reflected on a dyno.
Most tire manufacturers recommend that you replace the rear tire after dyno runs , so there is also that cost to consider if you have a dyno run!
 
Thanks for all the feedback... I have decided to try thr standard route and bought a reasonably decent collector and downpipes from Germany... I'm not bothered about noise and want the best low down and midrange running... We'll see how it goes but its all in the fun of meddling after all...:)
 
Bits arrived today... The downpipes are pretty well used but serviceable and the collector is in overall good nick... I can use this set up for a while and get the Keihin SS downpipes balance piped by a friendly engineering co (Shetland has plenty, especially serving the oil and fishing sectors...) using the orig pipes as a good pattern... Yum, can't wait...
 
I did fit the bits I bought and rode it for a couple of days this week... It restores the early part of the rev range and still pulls strongly in the midrange... I have to say after 10's of bikes and 25 years of year round riding, I prefer collector boxes and standard set ups as unless you get things done properly you nearly always make the bike runs worse at some point and always make it noisier... I may be alone on thinking bikes like Jap 4's/singles and nearly all BM's sound pretty shite when loud...:thumb
 
Rob Farmer said:
Pheew!

Glad it made an improvement ;)

i prefer a deeper quieter exhaust note as well.
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And even though the downpipes are well used the collector had stood up really well so the ss downpipes will work fine once I've added a balance pipe...:)
 
I cheated... I took a punt on a German breakers on ebay and it arrived quicker than a few co's in the UK...
 
Nippy Normans supply Touratech, Wunderlich, Desert Fox and many other makes of accessories.
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