Hi all, has the subject of back pressure been discussed in the past? - 1985 k100

If you are talking about your spine you can change the handle bars.
If you are talking about your wind problem you can change your diet which will reduce the pressure.
If you are talking about your bikes exhaust, numerous tests have been done. OEM has the best performance least noise.
Regards Martin.

So if loosing back pressure is a problem can i compensate for a drop - lets say by opening up the air intake or reducing the fuel pressure?

You need to post what symptoms you bike is experiencing. Why do you think you have a back pressure problem?
Regards Martin.

I dont yet i'm just sure there is a reason the standard exhaust is so intricate - oh and yes its coming off.

Its old Martin and to replace it would cost more than making a replacement.

There has been a lot of experimenting with various exhaust designs and aftermarket exhausts. And if you search there are dyno comparisons out there. The general conclusion is that there is no performance benefit to be gained.
Some might improve bottom, mid, or top end performance slightly but it will be countered by a loss elsewhere. If you are doing it just to create more noise then that will be achievable but at a performance cost. How much loss will only be determined by the design and by doing a before and after dyno. There are plenty of cheap OEM exhausts  out there for less than it would cost to either make or buy an aftermarket exhaust.
Regards Martin.

Unless your goal is more noise in an attempt to be safer, your best bet is to find a good used OEM exhaust.  My K100RS came to me with a well known aftermarket exhaust that embarrassed me every time I rode through town. 

I sold it and was able to purchase a very nice OEM exhaust for half of what I sold the aftermarket system for.   My bike runs better at lower mid-range and uses a bit less fuel.  And I don't cringe anymore at stop lights when I'm in town.

Motorworks UK have pre and post 86 K100 mufflers for 50 UK pounds. Headers 45 UK pounds.  A round trip of approximately 4 hours.
Regards Martin.

old can look good , if you do the work

before



after



and will be required to adapt any thing to fit

check out ben kinghams  work and parts he has to sell at bsk speedworks

http://www.bskspeedworks.co.uk/k-parts.html

just one of several places that make stuff for k bikes still today

good luck

Hey Charlie,

Do you do mail order? I could send you my oxidised, discoloured pipes (and OEM muffler) and you could send them back looking all shiny and new? Wonder what the postage cost to/from Oz would be? 

I keep meaning to start cleaning mine up as part of my Donna rebuild, but it's too miserably cold out in the workshop at the moment (it is so well built and draft free (not) that, this morning, I found snow had been blown in under the eaves and had filled my toolboxes). I had already told myself off for bringing the engine block into the warmth of the kitchen to do some helicoil work as a result of a few stubborn fasteners and a little cosmetic painting (it's back in the cold workshop now)!

Motad UK make a very nice (round) muffler for the Mighty K. I whacked one onto my RS about eight years ago, it's held up really well, and although there is a very very slight additional 'burble' to the note at idle it is not intrusive at all. Its performance level is essentially stock. 

Now, Charlie has a sweet Staintune on his RT and it's a pleasure to ride a coupla dozen metres back from him listening to that sweet metal thang sing!


After six years it still had a sweet patina, and scrubs up well.