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Discussion Starter #1
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.

Thanks,

Sidney Franklin
Bloomington, IL
 

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Never looked, but I would try the usual sites, megacycle, webcam, powroll etc.
There's bound to be something out there. Is that an 8 valve head like the 500?

FR
 

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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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Yeah, what he said. Putting a hot cam in an otherwise unchanged engine is not a good thing as cams, carbs and cans all go hand in hand. Most street engines are tuned for good mid-range performance, but if you go popping in a hot cam that wants higher revs to perform, you lose all power as now the motor has the wrong cam in it to perform in the low to mid range, and the carbs and exhausts are too small to make it breathe on the top end. The dude is right, get the boring bar and punch it out, go up a bit on the carbs and open the exhausts up a little. I ran a 750 Triumph Trackmaster on the dirt track circuit for a couple of years, and the engine was bone stock, but with 34mm Mikuni's (stock was 32mm), and a set of Supertrapps. If I had been running a lot of 1/2 miles, a set of different cams would have been called for so it'd wind a little more, but for the short tracks, nobody beat based on power (they beat me because they were better).

regards,
Dgy
 

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Discussion Starter #6
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?

Thanks,
Sidney
 
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