SJRoome
Registered user
Hi
I will attempt to describe the character of my 1989 R100GS when fitted with Keihan stainless downpipes without a balance pipe and the Keihan Y piece into the stock silencer. As this exhaust combination has been sold by Motorworks for many years there are lots of bikes fitted like this and I hope others will recognise my description.
The bike was very happy at large throttle openings and high rpm. Acceleration was powerful, and it would continue accelerating past my comfort level due to the load on my hands. It sounded OK. In the mid range the bike was less happy and had certain rpm ranges it liked and others where there was some vibration or appeared to be 'hunting'. This was worst at very low throttle openings or on the over-run. Careful tuning and balancing could reduce but not eliminate this. It was a pleasure to ride along empty roads where you could choose your own speed but a pain in slow moving traffic where the speed and hence revs were dictated by others.
I replaced the downpipes with a pair from BMW Boxer supplies that have a balance pipe and also fitted their Y piece.
When I test rode the bike with the new exhaust without any tuning I immediately noticed that things had changed. The stumble on opening the throttle from idle that used to make moving off at a T junction an interesting experience had gone. Acceleration is smooth and powerful and happens immediately without a small pause I did not notice until it was gone. The bike seemed happier at most speeds but appeared to vibrate at very small throttle openings and on the over-run.
I tuned and balanced the carburettors. Changing the exhaust did not require large changes to the tuning. It was however far easier to balance the carburettors since it was not necessary to pick an rpm to balance at. Once balanced it stayed balanced across the rev range.
The result is a bike that is smooth, responsive and a pleasure to ride at any speed. This was an expensive upgrade at over £600 so it won't be for everybody, but I am pleased with the result.
I will attempt to describe the character of my 1989 R100GS when fitted with Keihan stainless downpipes without a balance pipe and the Keihan Y piece into the stock silencer. As this exhaust combination has been sold by Motorworks for many years there are lots of bikes fitted like this and I hope others will recognise my description.
The bike was very happy at large throttle openings and high rpm. Acceleration was powerful, and it would continue accelerating past my comfort level due to the load on my hands. It sounded OK. In the mid range the bike was less happy and had certain rpm ranges it liked and others where there was some vibration or appeared to be 'hunting'. This was worst at very low throttle openings or on the over-run. Careful tuning and balancing could reduce but not eliminate this. It was a pleasure to ride along empty roads where you could choose your own speed but a pain in slow moving traffic where the speed and hence revs were dictated by others.
I replaced the downpipes with a pair from BMW Boxer supplies that have a balance pipe and also fitted their Y piece.
When I test rode the bike with the new exhaust without any tuning I immediately noticed that things had changed. The stumble on opening the throttle from idle that used to make moving off at a T junction an interesting experience had gone. Acceleration is smooth and powerful and happens immediately without a small pause I did not notice until it was gone. The bike seemed happier at most speeds but appeared to vibrate at very small throttle openings and on the over-run.
I tuned and balanced the carburettors. Changing the exhaust did not require large changes to the tuning. It was however far easier to balance the carburettors since it was not necessary to pick an rpm to balance at. Once balanced it stayed balanced across the rev range.
The result is a bike that is smooth, responsive and a pleasure to ride at any speed. This was an expensive upgrade at over £600 so it won't be for everybody, but I am pleased with the result.
