Power loss on a SF1

If fuel supply, ie, taps, lines and filters check out OK, check float heights.

Too low fuel level will have no great effect on low- and mid-range performance, but certainly plays a major role at WOT, especially if power for any length of time is demanded.  Engine seizure and holed pistons are very likely results...

piet
 
Picturess of the spark plug after it came out of the bike and after a little clean up. Pics make them look blacker than they are - it was more of a dark brown colour. Both spark plugs pretty similar.

What is the opinion?

Thanks

BTW I don't think it is an ignition reset as it was still running but giving reduced power so probably not rectifier related.
 

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chrissoz said:
Picturess of the spark plug after it came out of the bike and after a little clean up.
Click to expand...

Should never 'clean up' a plug wen you're trying to assess an engine issue ... every aspect of the deposit is an indicator of some sort. Noone has asked what heat range plug you are running - if you run even one grade too hot in the SF you will hole a piston at wide throttle openings and high demand. Your symptoms SOUND like fuel starvation (partially blocked main jet???) but could also easily be an indication of/precursor to a seized or holes piston. I'd be giving the carbs a total cleanout and ensuring you run a safe plug (I swear by NGK B9ES for the SF - and mine runs 10.5:1 comp). Is there any way the ignition could advance off the scale inermittently???!!!
QF
 
Had a look through the GPS logs and the loss of power was coinciental with maximum speed (130km/hr) and maximum vertical speed (125m/min) - i.e. thrashing it up a big hill. This would be when I would expect the fuel consumption to be highest.
To eliminate fuel flow issues I did some back of the envelope calculations and came out with 0.65 l per min. (est 30l per 100km consumption with the throttle open wide - at 130kmh gives 39l per hr or 0.65l per min). Will have a play with a measuring jug and a stop watch this weekend to see if the petcocks/filters/etc will deliver that flow rate.
Has anybody else got any views if those fuel flow calculation are anything like right?
 
I believe you will find the standard fuel taps flow more than enough. Always worth running with both taps on.
Sounds to me as tho your filler cap has temporarily blocked the vent.  I had this happen on my 79 JOTA on a trip years ago, when running a tank bag (as Vince has mentioned).  Only happened when accelerating hard.  Loosened off the tank bag straps and it didn't happen again.  Frustrating.
 
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