feetupfun

Leverage is the ratio of axle travel to shock travel. On a 247 the ratio is about 1.1:1, so if the shock travel is 100mm then the axle travel is 110mm. The bigger the leverage ratio, the stiffer the springs need to be to achieve the right sag. Also, the heavier the rider, the stiffer the springs need to be. For example I'm 94 kg and on a 1.1:1 rear end, 45 pounds per inch springs are about right. 40 pounds per inch springs on a Cota 247 would probably suit riders weighing between 70 kg and 85 kg.

Lighter damping in the shocks makes for less effort from the rider when un-weighting the bike, or getting a bigger lift with the same effort. Your 247 will handle fine in trials sections with either standard damping or light damping in the shocks. Standard trials damping is slightly better if you are also going to use the bike for trail riding. Lighter damping is slightly better if you only use your bike for trials riding. Suspension damping is the conversion of kinetic energy into heat for the purpose of controlling the up and down motion of the wheels and the up and down motion of the bike. Bike shocks use oil moving through small passages to absorb the kinetic energy. The heat energy gained by the oil is transferred to the atmosphere.

1. Tricky to get just right and increases seal friction. 2. Doesn't help to resist a long lasting compressive force like riding down a slope with the front brakes on. 3. If you have dual rate springs, increasing the preload will get you to the stiffer part of the spring travel sooner, but you may run out of spring travel before the sliders bottom and you may create a topping-out problem going up hills. 4. The best way.

S/S = Stainless steel? or single seat? or shelf stock? or something else?

The chain will wear faster. First gear may be too slow in places when you need a bit of speed and second gear may be too fast for tight stuff. It's risky to change gears in a section so most people have gearing that is the best compromise for their riding style and stay in the one gear. For many riders, it would be harder to ride smoothly in first gear due to being harder to balance and having reduced acceleration.

yes

10/48 (4.8:1) is 12% slower than 11/46 (4.2:1). 9 teeth front sprockets are available. Bigger (custom made) rear sprockets are available.

Changing the reeds to boyesen makes a small difference to the way the motor runs. The evidence of this is that the air screw and sometimes the pilot jet requires a change made when boyesen reeds replace the standard reeds. The difference is because there is less pressure drop through boyesen reeds because they are lighter. Maybe it is too small an effect to be noticed on your bike. When you fit boyesen reeds, the reed stops need to be removed for them to work properly. Maybe you are asking about bending the reed stops when using the steel reeds? That's not a good idea because it reduces the time-to-failure of the steel reeds and might allow the reeds to bend instead of flexing within their elastic limit. Low budget gains in bottom end response on a TY175 which is in good mechanical condition include increasing the compression ratio, lightening the flywheel and experimenting with the ignition timing.

Depends on what the seal is made from. The one in your photo is likely to be Viton. Here is a chart that gives operating temperature ranges for the various materials that seals are made from http://www.pspglobal.com/low-temperature-seals.html

I'm sure you can work out what's going on when you pull the clutch cover off, without a manual. They are very simple machines. From the sound of what you have said the shifter may have had a bit of a hit. My friend's 1981 349 had similar symptoms after the shift lever was bumped on a rock just before a trial and he laid the bike over on its side, took the cover off and fixed the problem and then rode the trial. If you can't work it out yourself, pull the cover off and post some photos up here and you will get lots of help

Left crank seal leaking is one thing of many things that could cause that. First thing to check is if the idle air screw has been adjusted correctly. Other possible causes include pilot jet restricted or pilot circuit restricted.

Does the piston really go that far down at BDC? What does it look like with the piston crown edge level with the bottom of the exhaust port? Also the piston should be in there the other way around, with the short skirt at the rear.

I can't see in there either

It's likely to have been stamped with the frame number of the donor TL125 for road registration/insurance purposes

The kicker in the movie photo is a standard top pivot kicker. It is the S shape design though which is standard for that era and different to later (straight) kickers

It wouldn't be the first Bultaco that has had the forks and front wheel fitted the other way around. Looks like the one from the movie has a different diameter front wheel. How long do you reckon it would run for with the fuel hose touching the cylinder fins and check out the brake pedal position. Pretty sure no-one rides this bike.

If you already have excellent throttle control you will manage fine riding trials on a 300 two stroke trials bike. If you want to jump up big stuff, a 300 is better than a 250.

Are you asking about the skirt protruding beyond the sleeve in the bottom photo? Or are you asking about the transfer port sleeve hole being partly obscured by the piston?

Logically how could those pegs ever fit to the standard Bultaco footpeg mounts? And they look amazingly similar to these which are listed as needing brackets welded on https://www.inmotiontrials.com/product/footrest-kit-alloy-universal-with-weld-on-brackets-wide/

To test the fan switch, an easy way to do it is to unplug the fan switch and fit an electrical bridge across the connector. To test the fan and the bike's power supply, unplug the fan and connect 12V DC from an external source to the fan motor.

If the clutch pushrod has any load on it at all, the clutch will slip. The adjusting screw in the clutch pressure plate has to be backed away from contacting the pushrod to avoid clutch slip. Do this adjustment of the screw with the cable disconnected then fit the cable and make sure the cable has some slack too. As for the kickstart lever not returning by itself, does it have a return spring fitted? Have you fitted both dowels in the gasket face of the magneto cover? Is the kickstart shaft straight? Are you trying to use the kickstart without the magneto cover fitted?

If you can accelerate the the bike hard in top gear without the clutch slipping then the problem is with the kickstart mechanism. If you find the clutch slips when you try and accelerate hard in top gear, then it is the clutch slipping that is causing the kickstart to "not engage". If you can't start the motor because you can't get the motor to turn over with the kick start or by push-starting in 4th or 5th gear, then the clutch is slipping or the primary chain is broken. If you provide more information about the recent history and condition of the bike, you will get more relevant help.

What bike?

Yes that's the standard setup on the MAR. It is an odd and quirky design. I did think about doing something for a while and was considering using a rear wheel hub with the brake plate on the same side as the sprocket so a simple brake rod could be used. If I was going to do that I would choose a wheel hub that also had a bigger diameter axle than the problematic 12mm standard axle. If you do change it to a more conventional design please post up photos.

There's lots you can do to avoid the clutch-sticking-when-cold thing happening but lots of people don't bother doing them and just get good at freeing it up. Are you willing to do a bit of work on the Sherco to stop it happening?