lemur

Yep, you have the most complicated and problematic carburetor design that was ever installed on a motorcycle so that they did not have to buy a fuel injection system from Honda. Most of the problems will be in the bottom half of the carburetor where the ethanol fuel evaporates out of the float bowl and leaves solids and corrodes parts, the top half won't be a problem until the rubber bits start to degrade and lose critical engine vacuum pressure. Avoid ethanol fuels if at all possible.

Tell of too much oil in your pre mix is how badly the exhaust plugs up with unburnt oil residue, naturally fuel rich condition intake also relates to oil rich. Your air cleaner filter needs to be clean and oiled correctly or that will starve the engine of air and lead to rich operation and poor performance, the reed valves need to seat perfect or scavenging pressure will force fuel and compression backwards through the intake so make sure the reeds seat perfect. Compression test is never a bad idea for diagnosis and future reference if you have the equipment. 👍

What octane fuel? If in doubt drop the main jet needle one notch and test ride it 👍

I suspect you are looking at DOT fluid; another test to try, mineral oil does not mix with water, DOT fluid mixes with water very easy. Only your clutch hydraulics would use mineral oil, brakes will always be DOT fluid.

Fortunately I am Canadian 👍 which means shipping is expensive, taxes are high and my money has low value (at the moment). I'd hook you up with Norm the OSSA god if you lived closer, he only lives 2 or 300 kilometre away and you are correct I am lucky to have lots of good rider friends 😎 several are motorcycle dealers and that helps too.

You can buy brand new forks and a brand new shock that fits right onto your bike which is relatively fast easy and expensive, used suspension parts are not worth my time and money unless they are local sourced, I need parts now and 100% working, not more parts that need fixing. International purchase and shipping of parts might be easy where you live, not here in North America, If my Ossa rider friend that owns about five OSSA bikes doesn't have the parts, they likely don't exist in my country, ymmv.

What country do you live in? Guessing UK only because you called it breakers but used parts are not something you shop for internationally. Shocks and forks are not something I would buy used anywhere and you can buy those items new without needing to be OEM branded.

Fuel tap on your bike is a little strange and over-engineered as a result of being fitted with a carburetor instead of fuel injection, Wheel bearings only last a year or three at best. Fork seals wear quickly if the slide bushings are not set perfect, note that when you get new aftermarket slide bushings you might need to do some careful hand file work on the parts to make them fit well, I clean and dry fit the bushings to inspect for clearance, fit or stiction and then finish the assemble.

Most rolling chassis parts and controls are very interchangeable between trials bikes, things like brakes, wheels and suspension assemblies are largely common between models and even manufacturers. We can almost tell you what all parts are going to regularly wear out and need replacement, wheel bearings linkage bearings, fork seals and slide bushings, brakes, levers, tires and chain. Most buy a spare air filter so you can always have one clean, oiled and ready to use. Tether kill switch is normally an add-on to trials bikes and a component that can often cause problems after some crashes. Being a 2007 model you should be replacing all fluids, brake fluid will be done by now if not already replaced.

Add the word Jitsie to your search 👍

I know what engine I would want to hold wide open until it runs out of fuel and not expect it to burn up, it's going to be the Honda.

Now consider the rpm the engine can pull:

Montesa 4-stroke is So much broader in the power band compared to any of the 2 smokes, there would be no keeping with it in the long run. 4T only fire on every other stroke and don't burn oil the entire time.

Unlikely the lubricant is the source of your clutch slip problems, you should have been making measurements of the plates and whole friction plate pack once assembled as well as the spring lengths. Obtaining a service manual is the best place to start if you don't already have one.

Viva Montesa 👍 Competition gearing preference is close ratio gearbox like an MX bike where enduro and dual sport typically used wide ratio gearbox. CR vs WR and once you ride both you will quickly develop a preference.