feetupfun

Yes there is a key on the crankshaft to make sure it goes back in the right place. I don't know what you mean by it having only one spark. It should only spark once per rotation. Yes it's normal to service the points with the flywheel off. The access holes in the flywheel are for the final step when you set the timing. Is it the Mk3 Lobito in your bike list you are referring to? Photos of bike/frame number/engine number of your Lobito may help your quest for information.

How about putting the bike on a stand and applying tension to the top run then to the bottom run. Apply the chain tension by putting the bike in gear and rotating the rear wheel back and forth. The idea of this is to replicate the conditions when it makes the noise You are not looking for the chain catching on anything. You are looking for a spot where metal can touch metal. Possibles include a worn chain guide at the front end of the swingarm or a worn chain tensioner block. Is the tensioner hitting the swingarm?

If it's the AMAL with a tickler, the usual reason people have trouble with cold starts is that they don't tickle them for long enough. Leaning the bike away from the side with the tickler also helps to get more fuel in. The pilot jet is important for hot starts.

The noise disappears when you pull the clutch in because that takes the tension out of the chain which allows the chain to move under the effects of gravity and inertia rather than being pulled into a straight line by the motor. When the clutch is out, one run of the chain is tight and the other is loose - under motor drive the top is tight and the bottom is loose. Under overrun, the bottom is tight and the top is loose. When you pull the clutch in and ride along, both runs are loose and the chain flaps around more.

It's normal to be able to change gears without using the clutch. Your clutch needs attention to get it to release properly. It's normal to have trouble finding neutral with the motor running if your clutch is dragging. Sticking throttle can be a problem with the cable or the throttle slide. A revving engine can also be a sign of an air leak into the engine.

TS 250 models R, J, K, L, M 1971-1975. I figure you are asking about the part that attaches to the rear edge of the flywheel cover and covers the front sprocket. https://classicjapanesemotorcycles.com/products/suzuki-ts250-rl250-sprocket-cover

Sounds like chain touching metal. Look for a worn-out/bent/mis-aligned/absent chain slipper/guide.

https://www.google.com/search?q=images+bultaco+199B&client=firefox-b-d&tbm=isch&source=iu&ictx=1&vet=1&fir=y4BZg-LQuKjJeM%2CUJInkK6fpaB9PM%2C_%3BUkyH0DRK_08fmM%2C0om8ErPu5Dg4TM%2C_%3BEAv52QZxkfZ_VM%2CqzYX65TOnxa2BM%2C_%3BvlROOjIwTh-NQM%2CqzYX65TOnxa2BM%2C_%3BQRz5mfyx_Ti4DM%2Co1G6319z_W26kM%2C_%3BKqRhQn-3dGRBNM%2CH131WeOsI8EraM%2C_&usg=AI4_-kQblQRQvlwkqMuYEnSgfbUc7LXzqQ&sa=X&ved=2ahUKEwi65MLr0dj4AhWR9zgGHSsBD3QQ9QF6BAgKEAE&biw=1366&bih=643&dpr=1#imgrc=EAv52QZxkfZ_VM

1:1 is zero leverage (Sherpa T pre-1970) 1.5:1 is high leverage for twinshock trials bikes (Godden Majesty 250/320, Fantic 240). Some twinshock MX and enduro bikes are even higher leverage. 1.1:1 is a typical for trials bikes made 1970-1975. With Falcons and your weight, if you get the 50 lb springs you will have zero risk of bottoming out the rear end during landings but the the rear end wont work quite as well as it could in rocky stream-bed sections. 40 lb springs would give a more supple rear end in stream bed. You should use the lightest springs you can get away with because if you aren't using all the suspension travel, the suspension action is not as good as it could be. If I was your weight, I would try the 40 lb springs first.

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.