trialsrfun

Ask Steve at Villiers Services but if I were to make a guess it could be a Greeves Challenger barrel with the fins cut back or less likely a DMW Marcelle? Can you post pictures of the head The Challenger barrel came in trials or MX versions but dont really know if other than the carb manifold and a spacer between head and cylinderthere was really much difference

If the carb is a similar type to that on the TY175 there is an O ring surrounding the main jet which needs to be a good fit into the float bowl when it is fitted. Remove the float bowl you will see it.

Lets hope an improving covid situation allows us all to ride in trials at least a few times but hopefully a lot more🤞 enjoy your trials collycolly 👍

Hi colycolly yes I did amend my post but what I initially wrote was based on factual experience. If ever there was a time to get the sport of trials riding both classic and modern back providing pleasure to its competitors it right now. The British bike section here on trials central has almost been killed off by whingers and moaners who constantly pick up on everything posted.

If you had taken the trouble to read the post before answering you would have seen that the person asking the question resides in France where the rules may differ from those your club may implement. TRAF also said the original carb had cracked and that he had the Mikuni about and presumably like the rest of us wants to ride his bike again. There has been precious few trials about for more than one year now yet as soon as there is the promise of at least a few to come you are whingeing. I notice that you ride an Ariel in Pre 65 events which no doubt is fitted with an AMAL Concentric carburettor these were not introduced until 1967. Amal (carburettor) - Wikipedia

Slightly off topic from the question asked, farmer 58za is your Cheetah fitted with the REH alloy cylinder with central exhaust port?

Everything TY is here, YAMAHA TY MAJESTY

The points side 36A magneto outer case with the round cover is perfectly okay for a trials engine. Is the flywheel fitted the all brass one or has it got the additional weight ring fitted to the outer face? Your bike appears to be a late model similar to the one shown here Sprite Motorcycles (historywebsite.co.uk) these had a longer exhaust on the right hand side, this was a big improvement over the earlier short type fitted on the left hand side making the engine run much better.

Make a saddle possibly by cutting a length of steel tubing in half longitudinally then weld a bolt vertically to the outside of the tube thread pointing upwards the correct length to secure the tank as on the above post, secure the saddle to the frame top tube using two Jubilee clips.

Gearbox oil should be GL4 spec as it is suitable for yellow metal bushes and not GL5 which 90s is. GL5 oil should not be used with yellow metal bush bearings. This applies to not just the Montesa but any gearbox used for any application which has yellow metal bushes.

There has been some discussion recently about SM Bultaco Hi-Boy frames, the attached link clearly shows the detail. Bultaco Sammy Miller highboy frame | eBay

This type of Montesa yoke, 247 and 348 are very similar https://www.google.com/search?q=montesa+cota+247+fork+yokes&client=tablet-android-samsung&prmd=simvn&source=lnms&tbm=isch&sa=X&ved=2ahUKEwiMwfmkhpTuAhVaQkEAHYqUD9MQ_AUoAnoECBEQAg&biw=1280&bih=800#imgrc=9nbHRrJsOC-6cM

A friend of mine built a Sherpa using fork yokes from a Montesa Cota 247, these seem to have possibly a 1.5° offset or run out similar to Sherpa yokes but place the handlebar mountings over the steering stem instead of behind it which gives more room on the bike. This for me being a taller rider gives much better steering and control. Steering bearing diameter is the same as the Sherpa, unsure if the lock stops or wheel spacers would need altering as the fork legs are slightly wider apart with the Montesa yokes.

http://www.yorksclassictrials.co.uk/classified-ads/4543674651 Paul Jackson (number on the website) is definitely the place to go for wheel restoration and possibly for the frame rear loop repair as well. Steve Sell makes a same diameter but much stronger rear wheel spindle which in my opinion is a must have on a bike that is ridden. If the original one is not already bent it likely soon will be, Steve is the go to person for all things OSSA. The rear brake cable on the MAR is much heavier made than a motorcycle clutch cable but Steve should have the correct one.

https://www.hpi.co.uk/

11 - 42 is what I run I find it spot on.

Paul Jackson look on the Yorkshire Classic website for his contact details. Wheel Building, Replica frames, cub PVL mounting and sprocket covers, general machining. Paul Jackson 01422 378 100

First thing is to replace the O rings in the carburettor float bowl, you will see them when you remove the float bowl.

Stand at side of front wheel, I then place my fingers over the twist grip while hooking my thumb over the front brake lever and squeezing the brake on, hold the brake on then with your right hand hold the wheel spokes at the three oclock position by the rim and pick the wheel off the ground and into rack like a one handed wheelbarrow. That's one end secured in the rack then lift the back wheel in however works best for you.

This topic has been both interesting and thought provoking with some great information. With regard to carb venturi shape and size some I have seen have a sort of keyhole or upside down pear shape for presumably faster airflow at minimal slide openings, might this design offer any advantage for trials use?

Going slightly off topic the exhaust system is a Mayfield expansion chamber. Back to the forks which are actually leading link not Earles type, if you are considering getting some leading link forks made then best to contact a frame builder, maybe look in Old Bike Mart

The leading link forks fitted to your Starmaker engined Royal Enfield are called 'Earles type' lots about them here http://www.vk6fh.com/vk6fh/earlesfork.htm

Thank you Section Swept

https://www.inmotiontrials.com/product/universal-rear-trials-plastic-mudguard-many-colours/ These are the ones I fitted You may be okay with this type https://www.inmotiontrials.com/product/universal-long-stilmotor-pair-mudguards-grey/ These are full length, they have a slower curve then the Goneli These https://www.inmotiontrials.com/product/universal-translucent-plastic-mudguards/ were on their stand at Telford in February and looked good, the rear is a little shorter than the stilmotor but that is a long guard so this rear guard could possibly be a good fit for your OSSA. The mudguard mountings on the bike are normally 6mm diameter I drill the guards 5.5mm then use 5mm bolts it allows for a bit of adjustment.

For my bike pictured above I used two of the short mudguards sold by in motion Bultaco. You will need to trim the length of the lower guard to get the right length.