lemur

Guessing you don't have access to electrical test equipment. If testing involves shipping in both directions or they just say it is faulty on receipt, it is generally best to just buy a new part. If your bike has no black box to control the ignition that means the coil and associated electrics will be even easier to meter test. Best luck with your repair 👍

Today 😎

And you would be correct, you are looking at the coil pickup or signal generator to control spark, that pickup generates a small charge of electricity when the magnets pass by it, that electric charge goes to your ignition control module where it will be used to send a whole bunch more electricity towards the ignition coil and spark plug. Coils have measurable resistance unless they are burned or shorted, then they will show the wrong resistance or no resistance at all aka no continuity. You can meter test the coils, meter test the connections and wires, you can meter test the power outputs once you have it somewhat running, but that part #4 the ignition control module is going to be by far you biggest problem to test or replace.

Lots of rectifiers or regulators would work, those are about the least 'special' parts in the whole electric system, everything else is more difficult to substitute and unique to fit the model.

Do you have a VOM (volt ohm meter) if you do then test for resistance (ohms) between the yellow wire coming out of the alternator and ground. Have you removed the flywheel yet? ... a photo of what is inside there would be helpful, we are looking for breaker points or a magnetic pickup to control when the spark happens.

This part does not comply with the wiring diagram, could be we are looking at a combined regulator rectifier part.

Everything you have there can be electrically tested easy except the ignition control module (part #4) you need a second running motorcycle of same model to test that part 100% certain. Make western union splice joints in your wire connections not pig tails, they work better.

Part #10 is your alternator, the diagram indicates it is single phase. That means there is a single coil inside the alternator and that coil will have some measurable resistance between the yellow output wire and ground. Output from that coil during operation will be alternating current AC well in excess of the 12 volts (or whatever) DC volts that your fan requires. The job of the regulator (part 18) is to limit the voltage from your alternator and regulators produce heat in that process, so regulator will be located somewhere appropriate to heat dissipation and cooling. The job of the rectifier is to convert some power from the regulators ~12 volt AC output to 12 VDC which is appropriate to your thermostat switch and fan motor. Incandescent lamps are happy to run on AC so that is why your fan is the only thing running off the rectifier. ... none of which has much to do with your spark ignition, that would be controlled by parts 10, 4, 11 &12. Alternator, Ignition control module, ignition coil and spark plug.

When my friend that rides Beta uses my fuel he notices it runs way better. Might have something to do with 98 octane and 1% oil that I run in my TRS bikes instead of his high test pump gas mixed at 80:1

They make that, it's called a Keihin 30mm PWK carburetor.

Main jet is plugged or float bowl is not vented to atmospheric pressure or your engine is not producing sufficient vacuum to make the carb work. Float bowl is not suppose to be full, it is suppose to maintain a level that is appropriate to the emulsion tube doing its job which is to initiate the atomization of liquid fuel into the intake path. The emulsion tube and main jet does that atomization of fuel by creating bubbles in the fuel but it can't make bubbles unless the fuel level in the float bowl is correct which is closer to half full not completely full.

I inspect all the small brass parts with a stereo microscope but not everybody has one of those.

After the float bowl is the main jet and emulsion tube which is the most common source of problems, that assembly can get pugged very easy. The carburetor operates on intake vacuum pressure to draw fuel up through the emulsion tube and jets.

That's how I test the float needle and seat operation and float height and it 100% works, if the float needle and seat is leaking or sticking or plugged you are going to see it.

So if you remove the float bowl completely and turn on the fuel tap, nothing comes out? That would narrow the source of your problems significantly. ... is that one of the carbs where you can accidentally install the floats in backwards or upside down?

Carburetor performance is dependent on the engines ability to move air. Highly recommend you inspect the reed valves, test the engine compression and the integrity of the bottom end seals first. The engine needs to move air efficiently for the carburetor to operate to its best efficiency and no amount of carburetor adjusting can overcome that.

How much would you pay to rent a trials bike at the venue with a hired guide, would be more interesting and as the renter how could you secure your investment in the likely event there will be damage to the rental unit and possibly the riders. Risky motorsport business is complicated as soon as you involve money. I allow a non groomed snowmobile trail through my property, also a freebie, also not a liability to me and there are hundreds in the same situation. I rarely use it myself, snowmobile trails are boring but as the land owner the trail has never been a problem.

You've set out great events and your contributions are greatly appreciated 😎

The reason I have guests here is so I have people to ride with, it's as much for my benefit as theirs, weather is improving here for winter riding and it looks like lots of stud season left 👍 That's my retirement plan in action, if your plan is to host for profit I think you are doing it for the wrong reason, it needs to be driven by your personal passion for the sport.

Stock original is just like the parts manual shows, every Montesa I ever bought new came with an excellent printed service manual and the bike will be just like the parts list shows. Best one I ever home built was from 1/4" Thordon elastomeric bearing plastic attached to the plate with large flat head socket cap screws.

From what I recall of a friends Fantic with the Dellorto carb his low speed adjuster was a fuel circuit and not an air circuit so logic when adjusting it might be counter-intuitive to typical. In the absence of a service manual 1 and 1/4 turns out is a good start point no matter what kind of small engine it is and I would expect to need to turn it in slightly on one of them. Sounds like you have the slide idle adjusting screw figured out 👍 the idle adjuster screw bumps up against a ramp machined into the slide, opposite side has a slot cut in the entire length of the round slide to follow a guide pin, intent being to stop the round slide from rotating. Been 6 hours so guessing you already have it running by now.

Respect is all I ever charge.

If they do it that way the vacuum sensor must be incorporated into the 4RT throttle body. Wasted spark is not a problem wasted fuel would be a problem, only makes sense they would need to inject only when an engine vacuum is present 👍

I would want to think the part called the 'ignition pulse generator' has something to do with ignition pulse generation.

Rule of thumb to determine if a spark is wasted or not is to look at where the timing in taken from. Crankshafts rotate at twice the speed of the valve camshaft so if it is ignition timed off the crank logic would dictate a wasted spark and if it is timed off the camshaft rotation that will happen half as often.