feetupfun

Think about what might happen if your bike is leaning against a tree or on its stand and while you are off somewhere else, it falls over. If your fuel tap is off, then the only place it can get out of the tank is through the vent. If you have the fuel tap on, you could lose your fuel out the carby overflow pipe Lots of bikes have slightly dodgy float needles too, and if the bike is left parked with the fuel on, fuel will also be lost either out the overflow line or into the engine while parked. It's a good habit to turn the fuel before you walk away from your bike. However until you also develop the habit of turning it on again when you want to ride, you will probably get a few fives by riding sections with the fuel turned off.

maybe wrong heat range plug maybe weak ignition system maybe sucking in gearbox oil when it runs maybe coolant leaking into the combustion chamber when it is parked maybe carbon deposits coming loose due to change of fuel type from previous use years ago Suggest you run it with a new plug then when it cuts out, have a really good look at the plug - strong light and magnifying glass - to work out what is happening to the plug. It will be either a fine (whisker) bridge made from carbon, or the nose coated with a layer of conductive carbon

If you use a spacer that has an outrigger bearing, then yes it does reduce the risk of bending the rear axle. Some outrigger kits from the 1970s are intended to be used with the standard dished sprocket (they fit on the outside of the sprocket) My 250 Explorer (which shares most mechanical parts with the MK2 MAR) came with mid-1970s 350mm Betor shocks which I suspect are the originals. I use 360mm Falcons for competition

When you say "....and dies away, check plug and no spark" do you mean that with a new plug there is no spark, or that there is no spark with the plug that came out?

One thing to remember if it your MAR still has the original AMAL concentric carby, is that for the fuel level to get high enough to run into the engine while tickling (which is what you want) you may need to lean the bike over a bit towards the side opposite the tickler. If you have the bike vertical or leaning the wrong way while tickling, the fuel runs out the tickler tell-tale hole, rather than into the engine. I have the original AMAL carby on my M49 Bultaco (and it still works beautifully) and unless I lean the bike to the left while tickling, no fuel goes into the engine, it all comes out the tickler tell-tale hole.

some montesas locate the rod centrally using the little end and some use the big end. Cota 348 is one that uses the little end of the rod. If that is your engine, 2mm each side is way too much and you should use a narrower bearing and spacers. Hard to help more because you didn't say what Montesa engine you rebuilt

Often when one of them has had the tank repainted, there has been filler used. Also have a look inside the fuel tank for rust

judging from the photos it looks like you are in the USA or Canada so I'll do my price estimate based on that. It looks to be in reasonable condition but how original it is depends on what you mean by original. It has aftermarket mudguards, seatcover and handlebars and everything else has been painted different colours to the original. The wear on the tyres does not match the odometer figure. Looks like a home-made fibreglass bashplate, but hard to tell. Original is fibreglass but thinner and neater-looking. If it was Australia, $1500. Being North America I would say $800 to $1000. The spacing between the gears is terrible for riding around town

That story about the zero gravity pen is a good story, except that it is urban myth. The Russians also bought pens from that US pen company that developed it and they used them on their own space trips

If you have a TK that is working OK I would stick with it. They work beautifully on the 434 model. Different story if it has a worn slide, needle or needle jet. My 434 still runs the original TK carby and it is the best running of all my TY250s I have often wondered why Yamaha went away from using TK carbies on the TY twinshock 250

I find that all the TY250 motors stall quite easily in some riding conditions if there is no weight band on the flywheel. If there is only dirt with good traction, I had no problem with running a flywheel with no band. If there is slippery or loose riding, I found a reasonable risk of stalling. After experimenting with no weight band on B and D model motors, I now use a weight band that is approx half the width of the BCDE model band and run standard spark timing on my B and D model motors. I run the standard flywheel with standard weight and standard spark timing on my A model motor. B C D E models here came with weight bands about twice the size of the A model weight band. By personal preference, I ride everywhere without touching the clutch which is maybe why I like a bit of flywheel weight.

Guy with the B and later model motors you can run them with an earlier spark than the A model without fear of stalling, unless the B or later model flywheel has been extensively lightened

Mine is an Australian SP370 and I'm pretty sure it was 6V, but the lighting circuit went to about 18V during normal riding without a battery. I only rode it with a battery until the motor was run in, then it morphed into an enduro bike using RM250C parts

Blowing bulbs was pretty commonplace at the time they were new. Yes they did not come with a voltage regulator so the voltage goes up and down with RPM. A simple way to avoid blowing bulbs is to fit 12V (or 24V) bulbs instead of 6V but they will not be as bright. Another option is to fit a ballast resistor in series with the lights to drop the voltage. Another option is to fit a rectifier and battery to stabilise the voltage. Another option is to fit a voltage regulator. The one I use on an SP370 that I ride without a battery is from a 1980s Husqvarna and it limits the voltage to about 13V so is perfect for 12V bulbs.

the routing of what looks like the ignition wiring up past the rear of the clutch cover is odd, with the magneto being on the other side. The standard wiring route on these is vulnerable to impact because it emerges from the bottom of the magneto case. A common mod is to reroute the wiring through the front of the magneto cavity in the engine casing to avoid problems. Maybe your wiring has been rerouted a different way to avoid problems. A skidplate from any of the MAR models should fit your bike. The first model MAR had a skidplate made from a composite material that was easily smashed to pieces with use. Later MARs had a nice aluminium skidplate, so there are less aluminium bashplates in existance than there are OSSA MARs

Those footpeg brackets have been added by a previous owner. Same for the bizarre sidestand mount It looks like a Mk1 MAR to me

Very likely to be the reason woody. From memory it was about 1mm that had to come off the steel spacer

yes the Yamaha OEM TY plastic bushes fit the Godden Majesty 250/320 swingarm. I did find that I had to slightly shorten the inner bush (the steel one) that came in the kit from John Cane.

Even with standard chain adjuster cams on a TY175, it is best to fit them one way when the axle is nearly at the front end of the slot, and the other way when the axle is nearly at the back end, because that way you can keep the handles/tabs away from passing rocks

The TY175 rubber carby connection to the reed block is offset to the left relative to the reed block, presumably to place the carby further away from the exhaust than if it was straight. As a consequence of the offset built into the rubber part, the inlet path hole in the rubber part does not line up with the inlet path hole in the aluminium reed block. By fitting a rubber connection from an RD350, the holes line up, resulting in less restriction/drag in the inlet. Further reductions in inlet drag can be gained by fitting a 26mm carby instead of the standard 22mm and using a better breathing airbox

that oil/petrol ratio should be OK. If the tank has not been relined to protect it from the damaging effects of modern petrol, I wouldn't put any petrol in the tank unless you are sure that the petrol you are using has no ethanol in it

When it reaches the rev limit of 2500, does it die, 4 stroke, 8 stroke or misfire unevenly? Does throttle position make any difference to its upper rev limit?

Making it the same number of links as the one that comes off is a recipe for problems because the previous owner probably took links out as the chain and sprockets wore.

I think it is the sliders that are machined rather than the staunchions The Norton sliders are machined to a larger ID The modern sliders OD are machined down to fit inside the Norton sliders (and held there with glue)

on some other Montesas that share that same casting, that cover is the cover for the two-stroke oil injection pump