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The clutch works perfectly the first time you use it from cold and also if it is left even for a few minutes. It doesn't work at all (no difference in feel on the clutch lever) after it's first use (i.e if you stop at a section and pull the clutch in all is fine. If you use the clutch a second time or more in the section then the clutch doesn't work at all - the bike keeps going!!!) Leave it a minute or two and the same scenario happens. We have tried new fluid, bled it loads of times, tried a complete new clutch and replaced the seals in the clutch casing. The only thing we haven't tried is the seals in the master cylinder - that is probably our last hope!

Nope! Been meticulous with all the parts (followed the parts book assembly!)

The new clutch was ordered as a sealed pack and included the steel plates and the fibre plates. We tried putting the old clutch back in and it was slightly better but not much. We also tried various podsitions of the lever "play" and the best was to have the adjuster on the lever screwed almost in to a point where the lever couldn't even touch the handlebar grip (didn't slip even when that far in?). We are pretty sure that it requires Dot 4 fluid as my own 04 bike has Dot 4 mentioned on the reservoir (his 03 doesn't say anything).

My mates 03 gas gas 250 is having random clutch troubles. The clutch works fine on first use but doeas not work at all if it is "pumped up" a couple of times as you would normally use it in a section. There is always pressure at the lever and doesn't feel different during use. It works fine one minute and then not at all - the bike just keeps going with the clutch in. To date we have bled the system at least 4 different times (new Dot 4 fluid), fitted new seals inside the casing & fitted new clutch plates. Anybody had any experience of this or got any ideas how to fix this random fault?

Jarvis won the event!

Go to http://www.gasgasmotos.es/web/eng/frame.htm and click on the link for trial (top left hand column)then select the bike and year in the right hand drop down box and then look for it at the bottom of the pge. It is a downloadable file in .pdf format.

Is anyone able to tell me the proper method of measuring & refilling front fork oil for an 03 pro 250 and an 04 pro 280. I beleive you can measure down from the top of the stanchion tube to the oil level but I am not sure if this is the recommended way. What weight of oil (for both bikes) does anyone recommend. Thanks

Excellent reply - very helpful and very detailed - thanks!!!

I had the piston & barrel checked by 2 different machine shops with their own micrometres and they both gave the same results to within a thou which is accurate enough I would think.

Thanks HondaRS. On thinking about it, you can't just go up a couple of sizes from measurements taken on the worn piston as a new "B" size piston (to match my own "B" size) will have a larger diameter. Really what info I need then is - what size is a new "B", "C" AND "D" piston so that I can check that buying a new "B" size will still fit my barrel correctly. Any ideas where I could get that info from? It is a Mahle piston and I have checked their website and note that Gas Gas is not listed in their list of Manufacturers they supply!

That's a bit OTT!!! Any help on this matter is valuable as I and I'm sure others are, learning a fair bit from all of the replies to any of the questions on this forum.

I had the barrel measured "properly" today and it read 76mm exactly (280 pro '04 model). The piston measured 75.91mm which gives a distance of 0.09mm (or 0.00354 thou). I have ordered the biggest size piston available (I 've gone up from a "B" size to a "D" size. Can anyone tell me the difference in sizes between the "B" and the "D" pistons. I was told it was 1 thou but now whilst reading info on the american gas gas website I note they mention each size increase is 0.05mm (or 0.002 thou). Therefore if I am going up 2 sizes, that equates to 0.1mm (not 1 thou) and I am worried now that the piston will be too tight in the barrel.

I've checked the small end bearing and it's fine. My last hope is that HondaRS's theory is correct and a set of piston rings will cure it or at least help it. I find it hard to believe that so much wear has occurred in such a short time. HondaRS - I checked the piston clearance at the point you mentioned and that is where the 4 thou size was though I had to be reasonably forceful (shoogle it about a bit but it did go up the gap about an inch maximum at this size!) Is there any way of knowing if the rings are badly worn before buying them? I would have guessed that there would be quite a bit of blowback down the side of the piston, past the rings, making the piston black - but there isn't much sign of it. Finally, I rocked the flywheel gently from side to side and there is a slight tapping sound with a very small movement somewhere along the line. I've checked the big end, small end etc. and there's no vertical play therefore my only conclusion is that the movement is indeed the piston rocking slightly in the barrel.

I have just checked the carb and all of the jets are as standard spec. and there is no evidence of any dirt or blockages inside. The only thing I have not checked is the fuel but I doubt if that will make the difference as I previously mentioned that my mate's 250 is fine with the same fuel. I have checked the spark plug and it's pretty black so it doesn't look as if it is running lean. Apart from piston slap has anybody got any more ideas?

I`ll try messing around with the jetting and report back. It starts rattling (definately not pinking but is a similar noise to tapping the exhaust with a spanner) just after returning the choke which is long before it heats up to temperature and is not 100% consistent with engine revs and can be slightly variable. The rattling continues throughout the whole rev range. As far as petrol goes - I am running regular unleaded which is the same as my mates 250 and his runs with no problems.