tony27

I would suspect Yamaha DT175 but not sure of exact model. 506 looks like pre80 model numbers

I was going to suggest www.claussstudios.com as they supplied the reproduction pipe for my TY250. Their eBay name is djia If you can find someone who is prepared to lend them the pipe off theirs then they will take a pattern off it & add them to their range

Guessing early 70s going off the shape of the CZ engine. I started trials on a CZ with the earlier egg shaped motor that I built a frame for, the motor was better than the villiers & bantam engines with more power & full circle crankshaft. Biggest issue was the charging system

Just for reference here is the OZVMX thread. Looks like you came to the same conclusion but I ended up finding the right piston & passed mine on to someone that needed it for a DT2MX which it was for http://forum.ozvmx.com/index.php?topic=29029.msg283770#msg283770

If you get a new piston make sure it is the correct 1, lots of pistons are listed as fitting but won't due to I suspect rod length Biggest giveaway that it won't fit is the bottom edge of the skirt, TY pistons are tapered out to the transfer cutout, DT pistons aren't & foul the crank before reaching the bottom of the stroke. TY pistons are noticeably lighter, I'll see if I can find a link to a thread on OZVMX I did on the differences after I bought the wrong 1

Basket is the same, not sure about pressure plate. Easiest way to find out is look on partzilla & select the pressure plate from the RL & it will show what it fits, if it doesn't fit the TM or TS with the rack then you'll know you need that as well

Ideally you'll need to remove the clutch pressure plate so that the pushrod doesn't stop you getting the cam back in, the cam is fatter at the end than the middle Undo & remove the adjuster nut & screw before trying to pull the cam out

Is the TM250 cover the type that pulls on the pressure plate via a rack rather than using a rod through the mainshaft from the left side of the motor? My RL250 had the rack type when I owned the bike but I never got to try the original set up to compare the 2. The rack type cover would allow you to extend the lever easier in theory

I use 1 of there systems in my CZ380 & run a iridium plug with the gap as it leaves NGK which is 0.7mm from memory, I wouldn't try adjusting the gap on that style plug as the centre electrode is really fine Never had a problem with hard starting, flame outs or fouling. My TY250 has 1 of their systems as well but I haven't used it yet, will be using the fine wire plug in that as well

Most forks I've dealt with seem to work best with a starting point of 150mm from the top of the tube with the fork collapsed & no spring, gets away from having increased amounts of oil after each change

Can't hurt, new springs & copies of the works damper rods would have to be an improvement over 40 year old parts

Always seems to be about 100cc hidden it the cases & clutch when you drain the oil

Pretty sure that it has been said for mono forks to work properly the steering head angle needs pulling in A different brake plate is also needed due to how the brake is secured on the mono fork

Have a read of the link in the heavy clutch thread, oil capacity is 700ml for diaphragm clutch models according to the very detailed write up

The 270 has more bottom end torque than a 250 which isn't a problem, the problem is that they produce a lot more power further up & will be a handful for a beginner

Being so close to the heat from the exhaust will have contributed to the short lifespan of the fuel lines

Using the choke lets in more fuel rather than air, more fuel cools the piston, more air leans out the mixture which creates heat. This is why air leaks are a major problem with highly tuned motors It sounds wrong but more oil means larger jets are needed as every extra oil molecule means 1 less fuel molecule getting to the motor

Flywheel holder, from memory the sort that is basically a large pair of vice grip with pins on 1 face work ok with the other side being ok for holding the clutch hub

Get rid of any damage that the key has done to the tapers, ant high spots stop the taper taking the load properly which then puts the load through the key Worse case will involve you needing to lap the tapers after filing off damage on the crank Make sure the o-ring in the cover is in good condition when you reassemble it or use gasket forming silicon on it

Kids can get away with lower pressure due to their lack of weight, 2psi isn't unusual for 1 that still weighs 40kg or less

When I rebuilt my motor you could move the crank up & down when the motor was still assembled. Bearings had never been done & motor was on standard size with so much end gap on the rings that I could turn the motor over by hand grabbing the end of the crank, with new bearings, seals & fresh bore there is noticeably more compression already To do the bearings is a full stripdown of the motor, if you need to do that due to play or rumbling then inspect every part in the motor & replace anything that isn't perfect along with all seals

If the bike is running fine I wouldn't bother changing parts I suspect when you need to replace the seals you'll also need to do the main bearings Vent hoses aren't a necessity for your riding situation but fitting a set wouldn't be the worse idea

The legs are generally clear coated which needs removing fully if you want to make them look better so it's not really just a cleaning thing

Can only tell you that it's not a v-force reed, if it was the cage would be plastic, have no screws & your manifold would have the wings cut off To tell whether you have boyesen reeds fitted to the standard cage will require a shot from the other side

What type of reed is fitted, if they are boyesen dual layer reeds they don't use stoppers. Any other brand on the standard reed block should require stoppers V-force reed block doesn't have stoppers