Ok Folks , brought a 400 from mate , never do that with recorded mileage of 9k (mot's to back it up ) but he couldn't get running right . I got running better but its gutless and has other issues.
Here the symptoms :-
On start up smokes , but clears .
Pulls fine up to about 4.5 k then misses ,no power can rev it up to 8 k but feel like it missing on one pot, hot or cold
Not go above 60 !! feel like sock up the exhaust pipe
Using oil but once warm there no smoke or horrible noises
Oil is blacken within 200 miles
Compression 25psi lower than my other 400f on no's 1/2 same on 3/4 as comparison only.
So how you going through the thought process ...and coming to a conclusion but first this is what has been done, with no effect :-
Swapped over Coils from running bike, carb sonic cleaned checked x2 and then swapped over with another set , electronic removed back to points, new air clean and plugs, advance retard mechanism checked
However you I can hear shouting it the valve steam seals !! ...that covers the startup smoke and oil usage agreed so lets whip the head off have looks see. Expecting broken rings as well
First this head been of before ! and came off to easy and the exhaust ports are very sooty
Umm lots oil so much the carbon comes off easy , note one no.3 pot is less oil and this confirmed by the colour of the plug
head
piston tops
So next was to remove the barrel , expect a ring to fall out ...hope all in one piece and then notice the are piston 0.5 O/S.
Bore with honing marking in place
So there looks to nothing to much wrong with piston / rings and quick check on the ring show all OK and no slop in bores .... could have been rebored wrong ?
OK move back to valves and just whipped one out and it clear the valve stem seal are shot see pictures but also note the perfect face on the valve (plus loads of oil)
So OK stem seals can account for oil on start up, oil usage,oil in bores (?) but it would still run Ok and given that there no oil appears to burning pass the pistons.
However I cant see that the seals would have such a dramatic effect on the power of the engine . Ok it can suck in oil and air and weaken the mixture but never this bad or has the thing not run in yet ?
Tomorrow I will check the bore/piston and all the valves
So what am I missing (apart from few brain cells !!)