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Help w/ XS400 engine modifications

13767 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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It's a 1978 XS400E with 11,000 miles on it. My brother bought it new and I started riding it around 1980. Finally bought it from him in 1988.

Forgive my ignorance about bike engines. I use to race Briggs go-karts and the first thing we did was swap the cam, mill the head, change the jets, and add a header. I'll leave the cam alone and look at punching it out. Already sent the front pipes to have them jet coated and I'm looking for some vintage looking slip-ons. Also pulled the stock air cleaner boxes and have been looking for K&N cone type filters. How big can I over bore this engine?

Neither of those sites list parts for an XS400.
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