zippy

I had forgotten about the difference in reed valve intakes

the Keihin carb should attach directly to the airbox rubber, no adapter. But it can be a pain in the ass to do. the adapter was for the smaller diameter Dellorto. GasGas Pro models 03 - 08 frame attached parts should fit GasGas Pro models 03 - 15 Engine parts should be interchangeable (Possibly as late as 2021, but not positive) Good resource for information at The Hell Team website https://www.thehellteam.com/technical-support/gas-gas-parts-and-service-manuals

Are you saying if you are in 4th gear and give the bike a lot of throttle (gas) the bike will shift on its own into 5th and if in 5th gear it will shift on its own into 4th? There is a known "clunk" and a little hard shift between 4th and 5th and back down from 5th to 4th, that is just a characteristic of the GasGas Pro transmission.

Probably a "certificate" is out of date.

Sorry, best I can do is Australian https://www.thehellteam.com/technical-support/gas-gas-parts-and-service-manuals

You have the TXT model before the Pro model came out. Frame matches the frame in the first photo I posted, look closely at the footpeg area. Also The exhaust header where it enters the midbox is horizontal, the Pro in angled at that point. The radiator on yours is "inside" the frame, the Pro the radiator sides are visible. 250cc vs 280cc, The Pro model has a number in the casting of the cylinder. Shifter side, 25 = 250cc; 28 = 280cc I don't know if the TXT model also has that number in the cylinder casting.

Throw up a photo and the hive mind will be able to tell you. Quick reference - there are other differences but this is quick: TXT model 2002 and before has a longer shift lever 2002 and later Pro model has a shorter shift lever Also frame differences

What is the finger height measurement? If it is too low there will not be enough leverage to disengage the clutch. this is from the 2015 users manual, finger height is 17.5mm +1mm -0mm, other years may have slightly different measurement specs. Credit goes to the Hell Team https://www.thehellteam.com/technical-support/gas-gas-parts-and-service-manuals

You just recently had the top end done. Was the bike running fine before that? definition of fine for this case: continuous running, only shutting off when rider wished to do so. was the engine removed from the frame or only the barrel, head, and piston removed? Start looking at what items were disturbed, disconnected, etc. Any sharp bends in the wiring that could have broken wire inside the insulation.

I think @Andy may have moved on to other endeavors. It has been a long time since I have seen any activity by him. I am not sure how often this site is monitored by him anymore.

and it doesn't take much to shorten the bars to where it is comfortable. I think I cut 1/2 inch off each side. Start small, you can always cut more off, a bit harder to add it back on. Risers won't mess with your ability to learn, being uncomfortable and in pain will mess with your ability to learn. Down side of using risers with low bend bars, it brings the center of the bar up so there is more possibility of hitting your body with the bars on big ups. Bars with a taller bend will give height but keep center of bars out of the way of the body.

OK quick arguing about whether tall or short is an advantage, it doesn't help answer this person's question. @dirtrider86 When you state "older trials" are you referring 10-15 year old machine or even older? - but either way my notes below still apply to both. I used to suffer from low back pain and sore wrists due to riding position. 2 small changes made all the difference so that I could support myself with my legs and not lean on the bars. 1. Bar risers - I didn't go crazy, I think I got the 10mm risers at V-Mar racing. https://vmar.com/barmounts.html#close - Same results could be gained using taller bars. and as @Tr1AL stated be sure to buy Trials bend, this is what they are designed for. 2. Bar width - I cut my bars shorter so that my forearm, wrist and hand were all in line. I will explain, this one takes some visualization to understand. stand on your bike, place your hands as far apart on the bars as possible - notice that your wrists bend outward and your back is bending forward Now bring your hands inward on the bars until your forearms and wrist are in a relative straight line. Your back will also move to a straighter position - you should be able to find a natural feeling position that is still somewhat bent forward. Setting the bar width for my "wingspan" solved the sore back from having a too forward riding position and solved the sore wrists from having them bent at an uncomfortable angle.

@arnoux I use that page many times and direct others to it many times. Thank you for continuing to keep the information available.

Nope, but a short while later I switched to Alpinestars and never looked back. So much happier with the Alpinestars, stiffer sole so my arches don't hurt.

Welcome, and good luck