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b40rt, curious, regarding setting up the suspension on these vintage machines, is your thought they should retain heavier damping, or should tne damping be lightened? Maybe not so little damping to fully mimic a modern trials machine, but maybe it should. From some easy simple rides at tne house, the lightened damping so far in the forks and shocks seems an improvement, just concerned that there is an edge of too lighly damped I prefer not to cross. FWIW, using the sometimes referred to push down test, the MAR at the moment has the forks reacting slightly faster than the rear shocks, when applying pressure onto the footpegs.

FeetUpFun, my OSSA came to me with oem shocks. I gave the oem shocks to my riding budding so we could try to build 2 good ones from 4 less good shocks. Show bike so fluid in them was less of an issue. Somehow I thought when I measured the Curnutts came in at 10mm longer but who knows. Ironically, comparing modern vs old, yes, new stuff is more advanced, but travel wise, these Curnutts have 4.7" of shaft travel so this gives the MAR just under 5" of travel. Not quite modern but more than the 3.5" ish they did come with. Hope tomorrow I can make my last mod for a bit. With like it will be pretty good, and the event Saturday could be proof of the pudding as they say.

Honestly, is 99% out mean it is accurate or incorrect. My guess is that yes, back then, all the brands were kind of designed to be a bit more damped. Riding the same bikes, in more modern sections, granted nothing crazy, seems less damping may be a bit better. Not so little to bounce around on the rear wheel, but just a bit more lively. The oem Betor forks came around easily and do feel much better with a fluid change from Mobil 1 ATF to Maxima 5 wt fork fluid. This was a drop in viscosity to about 16 cst from around 33. The rear shocks as I first built them up, I also used Mobil 1 ATF as back in the 70’s per the Curnutt rebuild instructions, they wanted type F ATF. I have since tested the original pistons at 5 wt Maxima fork fluid, and stayed with that, but have been enlarging the drilled ports in the piston. I enjoy working on suspension of all types. Ironically, not having even a simple rebound adjuster makes me appreciate having them on modern stuff.

Not sure what is stock length on a TY. On the OSSA MAR, if remembering correctly, the Curnutts are 10 mm longer than stock. Curnutts are 350 mm and not shortened, but could be easily. Too much experience working on suspension for mx and woods bikes and none on trials bikes is adding to the learning curve. Eventually, I will find the setup. If you do plan to possibly make a fluid change to alter damping, be cautious since true viscosity is very random when stated as a weight. I will add a link to Peters V chart, that list many fluids by cetistokes, which is an easy and better way to make changes. http://www.peterverdone.com/wiki/index.php?title=Suspension_Fluid

This past week I was talking about rear shocks and the forks on my and my friends OSSA MARs. His bike, he wants to replace the rears, currently the modern Betors. He is in email conversations with NJB, decided Rock Shocks are a bit more than he cares to spend. I did suggest he have a look at the Majesty shocks and also fork springs. As for myself, my OSSA has vintage Curnutt shocks on it, freshly rebuilt. New to trials, but not suspension tuning, I am learning that although these vintage bikes when new had very noticable damping, they are not as lightly damped as modern bikes. Saying that, I am learning that even though I am not hopping the MAR around, it is overdamped in the rear. With that, I have swapped to a lighter rated fluid, and even have been drilling the pistons for added flow. Time will tell if I am headed in a good direction or need to buy new shocks.

One point not mentioned in the previous oil discussion, is flashpoint of the oil. Yes the oil, however much or little is mixed with the fuel is headed somewhere. Most likely out the exhaust. High flashpoint oils seem better for and recommended for high rpm, higher output engines. Lower flashpoint oils tend to burn cleaner, and are oftened recommended to run a lower premix ratio, the higher the intended rpm. Oils that do burn, may produce carbon over time, while high flashpoint oils tend to remain wet. Synthetics of high flashpoints tend to leave a strong but easily cleaned oil layer, while castor oils tend to gum up unless run hot and often. With current technolgy, coatings, and exotic materials, plus some very high quality oils, the time may be near for mix ratios even higher tha 200:1. Sometimes though, our comfort level and instilled experienceholds us back. Admitting, I even consider oil inexpensive vs engine repairs, provided the engine performs correctly. Not debating anything, just sharing info.

The manuals suggest a 50/50 mix of coolant and water. Myself, keeping it simple, I replaced the coolant with what I use in the KTM. 70% distilled water, 30% coolant safe for aluminum, and the applicable amount of Water Wetter for the batch I mixed.

Agree, possibly overfilled and simply venting the excess. You might consider routing the overflow hose outside the bash plate and then watch for any signs of coolant, just to ensure it is not a waterpump seal or drain, gasket, etc.

Agree on checking the small adjuster at the lever. I am going through a 2005 SY250R I recently purchased. That engine, in the Scorpa chassis has a funky adapted hydraulic clutch setup. You might ensure no pebbles or debris are fouling the engines clutch arm movement.

6 volt AC voltage regulator arrived Friday. For my setup, I am running a 6 volt 10 watt headlight, and a 6 volt 5 watt tailight. I did not bother adding the brake switch and brake light or horn. The MAR apparently has 3 generator output coils besides ignition. The higher output yellow lead on my machine is for the headlight in original setup. Another coil was for the tail light, and the third for brake and horn. With my combined electrical load at 15 watts, the headlights coil, rated for 30 ish watts is more than needed. The original design, like many other 60’s and 70’s designs, utilized 6 volt AC to drive the headlight. By design, they matched the headlights requirement, to the ouput coil capability, and things worked. Voltage would climb and fall, but it worked. Same on tne other output coils. A couple weeks ago, when I first powered the lights, all was good, until I the rpm increased. Because increased rpm drove the output to max, and the bulbs could not consume the power, voltage rose until the bulbs burned out. I decided on getting. Kedo 6 volt AC voltage regulator. AC only, and no rectified DC as there is no battery or horn. If you plan to use a horn or flashers you might need DC for those to operate correctly. The Kedo regulator is supposedly a reproduction for a Yamaha XT500 and others. Electricity is not brand loyal, so it was an easy hookup. The regulator has a single yellow wire, that coincidentally matches tne OSSA yellow 30 watt wire. The regulator case is aluminum pot metal and must be grounded. In simple terms, the regulator is basically a controlled leak. Set in the 6 volt range, as voltage increases with revs, the regulator holds the voltage steady, bleeding excess to ground via an internal variable load. I mounted the regulator on my resto mod MAR to tne left side feame and headtube gusset. One small 6mm hole. The hole itself was burnished to remove powdercoat, and then to be certain, I verified low ohms from the burnished area to the engine center case. The reading was bouncing between 0.0 and 0.2 ohms. The wire hookup had me retain a single bullet female connector on the oem yellow output harness. For my homemade chassis harness, I installed a male bullet connector where I placed two wires. One wire ran off the lights, while the second ran to the regulator. The regulator arrived with a bullet connector crimped to the lead, so I simply made a match there with no mods. To save money in case this did not go as planned, I only installed a tail light bulb. I expected that for the cost it was smarter if it popped. Also, at 5 watts required, if the voltage was not regulated, it would fail easily. Fired it up, set the switch for lights and the tail light illuminated. With rpm increased, the tail light did not fail. AC voltage checks were bouncing about, but never above 7 volts. Ideally, this will not be exceeded at full revs. Installed a new headlight, and tested again still working. Not exactly sure if or how this could help others, especially if you must run power from all three output coils. But did want to share if needed.

Interesting about the reeds and water pump housing. On my SY250, reeds in it now are fibreglass with no true stoppers. The water pump housing is stock, but I did get the 2005 Scorpa options catalog with the bike. They show a slightly different housing where the fwd hose spigot extends more towards the radiator.

Ordering parts today. Expect good results and a simple solution. Not expecting lights to be superb for higher speed night riding / driving, but acceptable for daytime road use and night rides at slower trials speeds.

Reviving an older topic. The other day, I wired the 73 MAR for lights. The bulbs I used were 6 volt. No plans to ride at night. The first run the lights operated fine until I reved it while riding. both headlight and taillight failed. Checked the voltage and found far more than 6 volts AC. I operated both lights off the one designated wire for the headlight, yellow I believe. Since my headlight is 15 watts and the tailight is minimal the system was not heavily loaded except at idle. So with this said, it becomes apparent I need a voltage regulator. The easiest method would be to find a proven single wire style, that simply bleeds off excess voltage to ground. My KTM had a regulator like this, but was 12 volt. i can find many low cost regulator / rectifiers that are 4 wire. Guessing two feed wires, 6v AC and ground, and two outputs of 6v DC power and ground. Not sure if it is possible to utilize only the input side to regulate 6v AC, and cap the rectified outputs. Price is good at $10 delivered. Any thoughts.

Rode a bit more. Will give the 11/46 a chance. Not bad, just considering a bit slower in first could be a benefit and allow second to work better. Time will tell after the upcoming event.

Currently dished oem 46t rear. I sent an email to Pete at In Motion regarding the spacer bushing that goes between the countershaft sprocket and gearbox. They sell Talon countershaft sprockets, that may be stepped, so I wondered if the spacer is shorter. Yes, the modified nut is needed, plus the 10 tooth may require installing a chain slide on the swingarm. Can be done, just a bit more work. No doubt the ever so slightly longer rear shocks will make this worse on my bike bike. As I mentioned, it feels too low in 1st now at times, but other times no, but second is a bit too tall when first seems to low. I know, ride and enjoy...

Any idea if the gearbox internally, as far as ratios, is the same between your TR77 and my, TR72 I think it is, 1973 MAR?

Sorry Woody, stock 46t rear, so I had 12/46 I just swapped to 11/46. I just ran some numbers. Using the oem 1972 sales brochure I had the internal gearbox ratios. Based on the numbers, it does seem the current 11/46 second gear was taller than the 12/46 first gear by about midway between 1st and 2nd. I suppose, the true question is, how low is too low for 1st. My minimal experience has me considering using second almost as my main gear, with first for very slow sections. The current setup would make first still more commonly used, as second is probably too tall with 11/46. Just asking, not debating what is best. I honestly do not know. Just riding around the yard, the 11/46 first gear is easily ridable for slow no dab cornering and so forth. Almost leading me to think, even lower may not be an issue. Stock 12/46 gearing = 3.83:1 11/46 gearing = 4.18:1 10/46 gearing = 4.6:1 Internal gearbox ratios are listed as 1st = 4.31:1 2nd = 3.24:1 3rd = 2.40:1 Overall gearing with 12/46 1st = 16.50:1, 2nd = 12.40:1. 3rd = 9.19:1 With 11/46 1st = 18.01:1, 2nd = 13.54:1, 3rd = 10.03:1 With 10/46 1st = 19.82:1, 2nd = 14.90:1, 3rd = 11.04:1

Curious about opinions regarding front sprockets sizes and how they effect the selection of gears. Stock, my MAR had a 12 on the front. I have ridden the 12 since I finished getting the bike going. I see that 10 tooth and 11 tooth are available. Today I removed the 12 and installed an 11. After riding around the yard a bit, the 11 certainly is capable of being very controlled at low idling speed in first gear. So with first being lower so is second, Second currently with the 11 feels about a bit taller than first with the 12. Does the 10 tooth make second gear about the same as first gear with the original 12 tooth? Curious what others run and how it compared to the stock 12.

Yes, I saw that on Facebook. Hope they are able to make it work. I was honestly surprised Race Tech did not purchase Works Performance to compliment their expanding line of shop services, some of which seem very vintage bike related, such as brake drum truing.

I would agree with this. I have been on the MTB over 25 years. I have had a street trials bicycle for only a couple years. As for moto, as a kid I raced mx. As a total beginer at moto trials, many of the skills and techniques learned from technical mtb riding, not fast flowy smooth trail riding help on the motorcycle. Little things, such as weight placement, and momentum when needed come to mind. My trials bicycle is an Inspired Fourplay street trials bike with 24”wheels. Of everything I ride, and Tartybikes warned me when I ordered it, the 24” wheeled bike will be the greatest challenge to master. As difficult as it is, the carryover makes other stuff seem less difficult to ride.

Any idea what vintage Girlings these folks are looking for? Works Performance makes, or I should say made nice stuff. Recently I learned they closed their doors after about 40 years in business. Hopefully someone will resurect Works Performance. If that has happened as of yet, I don’t know. As the odd man out, because I had them, and they are both a high quality shock, seals are easily obtained, plus super easy to rebuild, I installed period correct Curnutt shocks on the back of my 73 MAR. There was some uncertainty of how well they would perform, but so far have worked very well in my opinion.

Bought the 2005 SY250R. Does not appear to have been ridden in competition and otherwise is in very good condition. Sent a second message to Birketts via their website page. Asked if they have stock on spares and if they had the mods posted somewhere on their website or archives. Hope to hear back from them. Plan to give the machine a good look over and replace all fluids and grease the steering and swingarm pivots. Also, since the mid exhaust tends to get punctured by the engine case, I will ensure that is addressed. Should be fun entry level and learning machine to compliment the 73 MAR. This trials riding is addictive, even when learning and being kind of a hack about it.

Thank you for the reply. Is there any chance you might have photos or can better explain the mods done? Most seem pretty straight forward, the frame tab to allow easier subframe removal is most intriguing. The repositioning of the thermostat seems obvious, but a photo would be a benefit. Still no reply from Birketts. I should message them again.

Honestly, more interested in the chassis mods.

Thank you both. Great info. Still no word back from Birketts.