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Help w/ XS400 engine modifications

13749 Views 7 Replies 5 Participants Last post by  Sidney Franklin
Anyone modify an XS400 for improved performance? Are cams available? Any OEM parts that are common? Does an XS500 engine fit?

Thinking valve job, and mill the head for a little more compression. Aftermarket Trumpet slip-ons, new jetting. Nothing crazy, just a little more power.


Sidney Franklin
Bloomington, IL
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what year xs400?

The xs400 was more popular overseas the here so I imagine there are some speed parts out there, you may just have to cruise foreign ebay. As far as a cam well anything can be made custom bit off the shelf brand new cams you are probably SOL stateside. for more power I always say there is no replacement for displacement, find oversize yamaha pistons or wisecos and do that first. a fresh bore job and bigger piston will do more for the engine than a hot cam.

As a side note I will never understand why peoples first instinct in hopping up a bike engine is always to change the cam. Even as far back as the 70's the japanese bikes were tuned to work very well with stock components and changes in parts like the cam or the exhaust without port work, valve work, or an overbore usually meant a loss in power. It may sound great but many jap bike owners lose up to 5 hp just by swapping to free flowing exhaust and pod filters (with hondas chucking the stock exhaust is still preferrable because it is a heavy mother) without other changes. There are very few stock japanese bikes that respond well to a cam change and little else.

First step on the more power chain is to go to a bike show and have your bike dynoed for a baseline (make sure to tune it up while on the dyno so you are making maximum stock power). Then probably an overbore if the piston is available, then maybe unshroud the valves, deck the cylinder head and install a pod filter (maybe a bigger carb) and a maybe a free flowing slip on can (after you hacksaw off the stock muffler). Then have it dynoed again and see if a cam is necessary. When dealing with moding uncommon bikes it is always good to chart your progress so you know what works.

as far as I know the xs500 engine is a parallel DOHC twin from the same family as the xs750 and will not fit in the xs400 frame. An SR500 motor however is very similar and the bikes share some parts (brake calipers on the disc models and other front end pieces) so it might be worth some investigation.

Edited by - Geeto67 on Jan 04 2006 6:44:35 PM
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