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Lost compression on it a few months ago in the middle of nowhere and have not had the room until I sold the XS400 to open it up. Went out today and had a fiddle. The bike is so easy to work on, from complete to topend strip down took less than an hour
Plug showed an indication of what to expect:
Head is fine, just needs cleaning up and a polish:
Yup, that’d do it:
Bottom of the barrel is fine:
Top has score marks tho:
Piston is screwed, although the rings held up:
Think it has a .5mm oversize bore and iirc means I may still have a rebore left in it after the one it needs now. Just need to price it up, work out if it was the wrong plug, wrong 2T mix, or just giving it too many beans.
Any tips on how to diagnose the cause?
My guess is running hot. Causes could be weak mixture caused by under jetting, or induction leak, or with bikes with the oil in the fuel – too much oil. I don’t know if the latter applies to yours?
Or something got in the chamber and glowed/rattled up and down?Any more?
Heh, one more conversation piece for the coffee table
I’d go with Andy on the running hot thing, certainly wouldn’t hurt to do a mixture check and plug chop when it’s back together again.
a friend has their own bike dyno and has offered to give me a hand sorting the jetting. Think the plug was the wrong temp too so when it is back together will get a jet kit and a few plugs. It is running pre-mix…. would too much 2 stroke oil make it burn too hot then?
I’d definately say it is running hot. Hard to say if it needs a cooler plug or if it is a fueling issue.
It is running pre-mix…. would too much 2 stroke oil make it burn too hot then?
Apparently, yes it does.
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