So I bought Stu Weyer's beautiful XS400 Cafe racer build (another thread on here) which has largely been an unmoving ornament for the past X many years.
I wanted to ride it but found that after it was warm in less than couple of miles engine ran horribly / stopped. Everyone from whom I sought advice gave me a similarly stern lecture "KN copy cone filters with CV carbs are cheap and shitty and bad news". Having frustratingly frigged about with them for a few days I find I fully agree....and found this gentlemen's excellent humour on the topic very helpful...
Anyway a couple of other folk, who are skilled bike tuners here in the UK, did suggest I try RAM Air foam filters. Another person suggested increase inlet tube length and match the volume of the original airbox. I've done both. Silicon tubing from carb to RAM foam filters approx 50mm in length then the bigger volume RAM Air foam filters. They still look cool. The bike is now running nicely when warm, takes a little patience to get warm, seems better on Reserve fuel setting but that maybe a red herring. It is running a little too rich which I don't mind very much as I understand just MPG efficiency and spark plug cleaning regime impacted. No smoky emissions just plug evidencing carbon deposits. I guess next step is to increase inlet tube length another 25mm (awaiting stainless tube). I believe the volume of the inlet tube together with Ram filters will then be approaching the volume of the original airbox and perhaps this may lean out the mixture. Maybe a balance tube, between intakes, would still be good idea but I don't think that will be needed currently. I hope that I'm going to be fine with the XS running a little rich as I can buy and or clean a lot of plugs for the cost +£700 for importing a pair of new Mikuni Flatsides to the Uk ....
I wanted to ride it but found that after it was warm in less than couple of miles engine ran horribly / stopped. Everyone from whom I sought advice gave me a similarly stern lecture "KN copy cone filters with CV carbs are cheap and shitty and bad news". Having frustratingly frigged about with them for a few days I find I fully agree....and found this gentlemen's excellent humour on the topic very helpful...
Anyway a couple of other folk, who are skilled bike tuners here in the UK, did suggest I try RAM Air foam filters. Another person suggested increase inlet tube length and match the volume of the original airbox. I've done both. Silicon tubing from carb to RAM foam filters approx 50mm in length then the bigger volume RAM Air foam filters. They still look cool. The bike is now running nicely when warm, takes a little patience to get warm, seems better on Reserve fuel setting but that maybe a red herring. It is running a little too rich which I don't mind very much as I understand just MPG efficiency and spark plug cleaning regime impacted. No smoky emissions just plug evidencing carbon deposits. I guess next step is to increase inlet tube length another 25mm (awaiting stainless tube). I believe the volume of the inlet tube together with Ram filters will then be approaching the volume of the original airbox and perhaps this may lean out the mixture. Maybe a balance tube, between intakes, would still be good idea but I don't think that will be needed currently. I hope that I'm going to be fine with the XS running a little rich as I can buy and or clean a lot of plugs for the cost +£700 for importing a pair of new Mikuni Flatsides to the Uk ....
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