feetupfun

You are right. Parallel yokes means that the tubes and the steering stem are parallel. If the tubes are in the same plane as the steering stem, that is called zero offset clamps. Zero offset clamps may also be parallel clamps. Angular offset clamps add another degree of complexity/sophistication because they can keep the steering geometry closer to ideal through the suspension travel. In my opinion, Bultaco Sherpa T and Yamaha TY twinshock clamps have a very well chosen amount of angular offset. The total offset of a front end includes the amount the axle is forwards of the fork tubes centre line, as well as whatever offset is built into the triple clamps, and the length of the forks from top clamp to axle. It is possible to reduce the steering rake without modifying the frame. The most common method is to lower the front (slide the tubes upwards) or raise the back of the bike (increase the spring preload, or fit longer shockies). Another way is to use eccentric sleeves on the steering head bearings.

what's the question?

also check for: a twist in the swingarm (wheel axle not horizontal) (common) the arms of the swingarm being bent off to one side (rare) the rear frame loop being bent to one side (common) the wheel rim not being centered on the spoke flanges (rare) the main frame bent in the middle (puts one swingarm pivot hole ahead of the other) (rare) The shockies being a different length when fully compressed (maybe only one has a bump stop) If you haven't worked out what the problem is by this point, I suggest to start with, you take the seat, seat surround, rear guard and end muffler off, pump up the rear tyre, set the axle adjusters on the same notch, set the bike up so the steering axis is vertical and have a look at how vertical the back wheel is and what the chain alignment looks like Then take the shocks off and see what happens when you move the wheel to the top of its travel

I am pretty sure there is no such thing as cheap shocks that have a good action. I have been using Falcons for about 15 years now and can say that they work beautifully straight out of the box and are lots cheaper than Ohlins The most popular trials twin shocks where I live are Betors, which are a bit cheaper here than Falcons, but I find their action is not as agreeable

Kevin, we are about the same weight. I found that my TY175 forks were OK most of the time, but there were a couple of things that they did: When you are loading up the front end under brakes, like when going downhill on dry, grippy rocks, there was noticeable flexing of the front end When you do medium or bigger landings, sometimes they would bottom out I tried quite a few things over the years to improve them including stiffer springs (from a TM125), air caps, heavy oil and while these things improved the bottoming resistance, they made the action of the forks worse in small stuff, and didn't reduce the fork flex Some time in the early 2000s I fitted a TY250A front end and ran it standard to start with and was pleased with the bottoming resistance and reduced flex. A while after that, I saw a video of myself riding a rocky stream bed and realised that I was using less of the fork travel than I wanted. First off I reduced the preload from standard until I got the laden sag to 50%, then later I replaced the preload spacers with short pieces of fork spring (this reduces the spring rate) and again set the laden sag to 50%. I run 10WT oil 125mm from the top, fully compressed, springs out. I'm quite happy now with the spring settings of the forks but may yet do some development on the damping. As far as how high to set TY250 tubes in the clamps, you will find that the TY250 tubes are shorter than TY175 tubes by about 20mm, so your front end will be 20mm lower than your current setup if you set them flush with the top clamp. The TY250 triple clamps have the same geometry as the TY175 triple clamps, they just differ in the size of the tube holes To get the right preload setting for you and your springs, you can measure the laden sag with you aboard with all your weight on the footpegs with the standard preload spacers, then fit shorter and shorter spacers until you get the sag up to around 50%. You will probably end up somewhere around the 1 inch preload as suggested by bestrcpilot. Yes PVC pipe is OK.

I had a ride on that EM5.7 used in the youtube video last weekend and greatly enjoyed it. It is certainly very different in response to a petrol motor, but I reckon I could get used to it. The thing I liked the most was that there are less things for your mind to deal with while riding. It was uncannily relaxing to come to rest, balance, then ride away without any brainpower being used managing a clutch and avoiding stalling. I recommend having a go on one of you get the opportunity

it is very hard to get the goo out of the pilot circuit and your symptoms do sound like that might be the problem

It might be what Tony says, or it may may be the shift mechanism centring spring. There is a centring spring for the shift mechanism that lifts the shift lever back up after you shift down a gear. It is visible when you take the clutch cover off

Another option for the rear axle: I used a TY250 twinshock swingarm axle as my OSSA rear wheel axle because mine had been straightened a few too many times, and I don't think that one was the original either.

The induction tract is under vacuum when the motor is idling, so if there is a leak, air will be getting in, causing the motor to run faster and leaner than it should. If carby cleaner or WD40 gets sucked in through a leak, the motor will change RPM. This helps to locate the site of the leak.

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