feetupfun

Lowering the gearing will help in the tight stuff because you can ride slower with the clutch out but it won't help the engine braking/power surge when you are on and off the throttle. That is a normal 4 stroke thing. If you have only ridden two strokes in trials previously it can take a while to get used to the characteristics of riding a 4 stroke in trials. Riding technique can also help as in using rear brake to control the bike in the tight stuff. Increasing the idle RPM will reduce the engine braking effect.

No, the level is not critical. Just drain it as well as you can through the drain plug hole, add 700 ml and you will be doing what Yamaha intended. If you want to check that there is not too much oil in there, park the bike level front/rear and vertical side/side, leave it for at least 24 hours like that and then take out the level screw and see if oil comes out.

I don't remember having that drain plug on my 1993 TY250Z. I just looked up some parts fisches for later TY250Z models and from those it looks like that plug was a change that was introduced after the first model TY250Z. Both drain plugs are in the gearbox section. Two possible reasons for that second drain. 1 It could be for where a switch is fitted to some other Yamaha model that shares the same engine casing and has a neutral indicator (perhaps TY250Z Scottish). 2 It could be so you can drain the oil without removing the bashplate.

I have not noticed any drain plugs in the clutch section. From what I've seen, the clutch compartment has the filler hole and the level screw hole. Maybe share a photo of the drain plug you are seeing

Leave the oil level screw in place while you are adding oil and put the whole 700 ml in. The reason for this is that you are adding oil to the clutch section of the transmission and it takes a while for the oil to flow from the clutch section to the gearbox section. So the oil level in the clutch section will be higher than normal until the oil levels have equalised in both sections.

Have you found a manufacturer of conrod kits for Bultacos other than Italkit?

I don't have a non-points MAR flywheel for sale at the moment. Aren't there any OSSA specialist parts people in the UK? There are some in the US who would probably have what you want. What's wrong with your points ignition? I've never seen an MAR with points ignition to know what other bike shared the same stator setup. Maybe it's something common

option 1. Buy a non-points OSSA flywheel and the In Motion ignition option 2. Buy an ignition from somewhere else https://www.francetrialclassic.com/en/ignition/5010-ossa-250-350-electronic-ignition.html

In Motion Trials (UK)

There should be clearance there. Having new parts does not mean that you are guaranteed the correct clearance. It would be risking damage to run it without clearance. If you need to, make the spacers a bit thinner. Aim for about 0.5mm total clearance.

I didn't mention the key or keyway on the left end. Yes it's common for the key on the right hand end to fail and chew out the keyways and the shaft because it's a dodgy design and people sometimes don't tension the nut properly or they sometimes fit a key that's too long. Depending on the amount of damage, you might be able to get away with machining the keyways wider in the crankshaft and the sprocket and fit a wider key.

So it's just the drive end of the crankshaft that is damaged? It's probably more common for the magneto end to be damaged by the bearing seat wearing the crankshaft down. I've got some with damaged magneto ends and good drive ends so you might be lucky and find a model 80 crank with a good drive end somewhere near you. My comment about the balance holes in the crank wheels also applies to 325 crankshafts being different to 250 crankshafts. Another thing is that early 325 crankshafts have the same diameter crank wheels as the model 80 but after about 75/76, the 325 got bigger crank wheels which will not fit in the M80 cases.

Not certain, but I think the M221 might have two ball bearings on the drive side while the M80 has one ball bearing so the bearing seat on the M221 crankshaft might be too long for the M80 motor. This may not be a show stopper though. It just might mean that you also need some other M221 parts as well as the crankshaft. The other thing to think about is that the 175 crankshaft will probably have different size balance holes in the crank wheels to suit the (lighter) 175 piston. What is it that is stopping you using the M80 crankshaft? (be a bit more specific than whatever being mullered is)

Cool video Bailey. Good to see. I'm now following your Youtube channel David Lahey

Your Lobito would originally have had an ignition switch of some sort for stopping the motor. Decompressors are commonly used for stopping the engine at idle but may not stop the motor when it is in a runaway situation. Lanyard breakaway kill switch and latching kill switch are effective devices for killing the engine in an emergency situation. The lanyard kill switch is the better of the two because the ignition is usually cut off sooner than with a kill switch.

Here's one advertised in Australia https://www.motorcycletyrewarehouse.com.au/300-23 It's a Bridgestone TW9 tyre

Yes it's a normal thing to have the tube creep inside the tyre. It can be quite persistent. If you can get the tube to adhere to the inside of the tyre it won't creep but that can be difficult to achieve. I've found it is less likely to creep if I use a 4.00-4.50 tube rather than a 3.50-4.00 tube. I have also found it happens less with Michelin X11 rears than with IRC rears. If you leave plenty of room in the rim hole for the valve stem to lean over I've found that the tube will only creep so far and the tube stem stops it creeping further (I found this because I got sick and tired of moving the tube stem back straight when it leaned over due to tube creep.)

To stop the motor, the kill switch creates a short circuit from the low voltage ignition wire to the bike's earth. The low voltage ignition wire runs from the flywheel stator low voltage ignition coil/points to the low voltage connection on the HT coil. The HT coil is usually hidden by the fuel tank. On the Bultacos I have worked on, the low voltage ignition wire is coloured black. Bultacos like yours originally came with a connector strip for the wiring on the frame under the front left of the fuel tank. If that is still there, one wire from your kill switch may be connected to the ignition wire using that connector strip. The other wire from your kill switch can be connected to the frame where the HT coil attaches to the frame. If you are still in doubt, post a photo so others can see what you are dealing with

Well the right hand side engine casing is from a Mk3 Lobito. A proper ID of the bike (and the motor) needs decent photos of the bike and the motor

I've seen that on many Mk1 concentric AMALs

With no thrust bearing the release mechanism parts that are rubbing together may have suffered damage from the heat generated by friction. The effect on the bike will be similar to a clutch that doesn't release fully but not exactly the same because this issue does not transmit additional torque to the gearbox like dragging clutch plates do.

The other brand manual is Clymer

There are a couple of workshop manuals written in English for 5 speed Bultacos that are useful. One manual is in the Haynes series and it's pretty good. I just looked and there is at least one advertised second hand on eBay. Search for "Haynes Bultaco Manual". If you have a Mk3 Lobito it is a 5 speed motor and the Haynes manual will cover it.

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?