pmk

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.

Agree, timing is probably a key to these bikes based on what I read. Based on what Benz wrote a while back, seems a few of these mods could be valid still and while may not increase performance per say, could make it more consistent to ride. I copied the words and info from Benz post a while back. Others may have additional small changes. Sadly, Benz may have been enjoying his bike so much, he never added any more info or sorted out how to post photos. Mods that have been carried out are as follows............. 1) sump guard trimmed on water pump side 2) frame modified so complete rear end,airbox and silencer come off by just removing 4 screws and undo carb rubber 3) thermostate repositioned into water pipe coming from cylinder head 4) beta throttle spring in carb to make throttle lighter 5) larger AJP clutch master cylinder,much lighter than standard 6) carb has been set up by Birkett but as yet i do not know jet sizes 7) reed bloke has been modified,again by Birkett,again i have yet to investigate Benz I did contact Birketts and await a reply Like this

My reading about the bikes here, seemed to indicate the UK machines came with the heavier flywheel and retarded timing. Everywhere else in the world supposedly got the lighter flywheel and advanced timing. The machine I get will be USA version. So I assume, but can check the timing.

Exactly, I had read through many of the Scorpa topics and posts. That one you linked to really caught my interest. Was hoping someone might have more details explaining a bit more in detail for tne less obvious changes. Also read, Birkett removed the studs from the cylinder and used capscrews. This allowed removing the top end without removing the entire engine apparently.

I will probably send an email, but was curious if anyone may know. Sounds as if they took the time and dialed in a few things to make a bike that was deemed very good, even better.

I have read many references to SY250Rs that were modified by Birketts. Unfortunately, nowhere have I seen it posted what all these mods were. Does anyone know what mods were done, and if they could still be viable today or just not cost effective?

eBay an original type.

You might consider carefully polishing the o ring area of the shaft using Scotchbrite or super fine sandpaper. Then, use tne original o ring to get a size for it, then try a firmer rubber compound such as a 90 duro type. Then again, if the case has corrosion pits in the o ring groove, it may be best to modify the case for a seal.

The bike is together, and now has a bit of ride time around the yard. No issues, and very pleased with it. When I went to buy spark plugs weeks ago, I thought I got the correct one. I searched the internet quickly and found recommendations from heat range 8 to 5. I read that BP6ES was correct, and it did cross reference to the ages old Champion N9YC I removed. I now suspect, having seen other references to BP7ES being correct. I have pretty much ruled out the heat range 5 and 8. So, for a 1973 MAR 250, is it a NGK BP6ES or BP7ES? Ready to get the jetting fully sorted out, and prefer to do it on the truly correct plug.

Had a look at how Trailtech does the sensor and magnet install. They glue the magnet to the hub and position the sensor on the brake cable. This is for cable operated drum brakes same as the OSSA MAR of mine. Downside, the Cateye computer I have would need the wires extended, or I need to find a long wire kit. Not really wanting to splice the harness. Done it before on bicycles and those wires are tiny. Need to get by Aldi and see the wireless one they offer.

I saw your photo in another section, I think the machined parts topic. This being a vintage machine, the front brake is cable operated and snakes around a bit. Also, how did you mount the sensor close enough to the magnet on the wheel. Do you have a photo of the fork and wheel setup.

Took a little bit of Google search effort, but no big deal. These computers you mentioned are known as Bikemate brand, and here in the USA are carried by Aldi stores. My thought is Lidl and Aldi may be the same company or related. While traveling a couple of years ago, we did pick up some items in Aldi while in Ireland. Locally, Aldi has a store very close to home. On a downside, Aldi built the warehouse and distribution facility very close to home, and in doing so, tore down a large wooded area I used as a riding area.

I had mounted the computer I dug out of my bicycle stuff. On the OSSA it needed to mount to the left of the left side bar mount. In regards to the magnet and pickup, normally the gap must be pretty close for it to operate. With the sensor nearer the top of the fork leg, how were you able to get the magnet close enough to work.

That method makes it simple, though more expensive. A very good option though. I had a look at GPS bicycle computers, yes there are some lesser brands for less money. Need to ask my bicycle friends if they have something no longer used.

Just went through some mtb stuff I have. Tried to install a wired Cateye. Looks as though the movement of the brake cable will be too much for the wires. Do you have any photos you could share, of how you installed it on the Beta.