The source of the problem you described must be something else, like clutch cable maladjustment or warped clutch plates, which can all be a source of a clutch dragging when you switch into first gear and engage the clutch. The increased slipperiness due to the friction modifiers used in synthetic oil could indeed be a possible source of clutch slippage but only under load and thus with the clutch engaged, not with the clutch disengaged as you mention.

If the bike starts moving forward when the clutch is disengaged and is in gear, that means there is excessive friction between the friction and pressure plates in the clutch. The clutch plates are not completely disengaged, and thus 'drag' each other along. Your argument doesn't hold, as the friction modifiers contained in synthetic oil reduce friction compared to mineral oils with similar viscosity. So if the bike lurches forward when kicked into gear, the 'clutch drag' problem should be even worse when using mineral oil. The 'clutch drag' problem that your bike suffered from is in fact the opposite of the problem you referred to with respect to the use of synthetic oils. The problem of clutch slippage when using synthetic oil usually occurs when the engine is working under full load, so at high revs and/or under full acceleration.

This said, forget about semi-synthetic oils, it's the biggest marketing scam in the lubrication business. Either spend more on fully synthetic oil or save your money and buy a good quality mineral oil and change oil more often. All my thumpers run on fully synthetic oil and I never had a problem with clutch slippage with any of them(*), even racing enduro's in the tropics or adverse travelling conditions (high temperatures in Africa and Asia). But that's only my experience, some might have experienced otherwise.

(*)Currently own 13 bikes. Apart from my XR650R, my four KTM EXC's (2x450, 520, 525), KLR650, BMW F650, and two XT350's all run on synthetic without any clutch slippage.

I agree with your point that semi or synthetics should ease the problem of a dragging clutch rather than worsen it.

Why do you say that semisynthetics are a scam? You may be right but what's your evidence?

Heard about clutch slippage due to synthetic oil before... but not sure if its true.

Lots of my riding buddys were using "MOBIL 1" when it was first introduce here (in the mid 90's in think) mostly sportsbike though. They also had the same problemo! eversince that I always have the impression to stay away from them.

like Rich said: use the reasonable ones & change it regularly than keeping the good ones...
btw Rich whats the measurement for the oil? 3litre right? its not in the manual...

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From memory without looking at the manual, (mine sure does have oil capacity in the manual) the XR650 takes 2 litres of oil in total from new or when rebiult, but when changing the oil and filter its about 1.7 litres but you won't get 1.7 litres in in one go without getting it kicked over or running to circulate it a bit.

Although it seems strange, it is a fact that some engines (mostly hondas) have a clutch problem with synthetic oil.
Synthetic oils "stick" better to surfaces, that is part of their good characteristics.... except when the space between clutch-plates is very very narrow. The oil-film that "sticks" to the clutch-plates is causes the plates to be "sucked" together.
This causes a "sticky" clutch, difficult and noisy gear-shifting and a problem getting it in neutral.

The same effect can occur when you use oil that is to "thick" (wrong viscosity).

If this problem occurs, just "stick" to mineral oil

Happy miles,
Maarten

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I have synthetic in my bike at the moment and i have heard that if you change back to mineral the oil will sludge, is this true and if so how can i get around that.

thanks guys

That used to be the case with the early synthetics but I don't think its still a problem.
If it concerns you do a change to mineral and then another after a few miles.
This should flush any remaining synthetic away.