Backfiring Montesa 4RT

[billyt]

Jonnyc21.   

My bad I should have said ECU not CDI.  

The Montesa does have a standard AC alternator (USA verbiage vs UK verbiage) .  

It also has an AC  "pulser" (see attached Montesa schematic) or trigger coil beside the alternator.

While the alternator is making AC voltage the pulser AC coil (trigger coil) is telling the bike when to fire (adjusted by the ECU & CDI box etc.  

When the bike is running pulling the lanyard sends a ECU pin to ground telling it ignore the Pulser (trigger coil and does not send signal to the CDI box and high voltage coil.

When the bikes running and in gear when you put too much load on the back wheel at low rpms it stalls the engine.

When the bike stalls the AC trigger coil no longer ses a rotation AC pulse going in the ECU box so it kills the bike. 

This scenario can be the same on a 2T carbed trials bike. Too low an RPM  in gear and a heavy sudden load can cause a mechanical stall of the bike as it does not see any AC voltage coming from the alternator and pulser trigger coil to the ECU unit. 

I still think it is weird logic Jimmyl is stating.

I do agree stopping the bike I gear with the clutch is a bad thing to do but purely from a mechanical stress level. 

Edited February 10, 2022 by billyt

[billyt]

Right off the Montesa manual. Pulser coil (Trigger coil)

[jimmyl]

Just my experience of 12 yrs 4rt riding and chatting with others 

bike always starts better after being stopped with kill button/ lanyard than a mechanical stall

 

Edited February 10, 2022 by jimmyl

[billyt]

Same here Jimmy 

42 years of riding only trials bikes. Several Montesa 4T  Scorpa 4T  Beta 4T and many Beta 2T trials bikes

We all have our experiences and that is good overall for the sport that we share them 👍. 

[IBA4rt]

I recovered the post although I considered my problem solved after changing the fuel, which I had published in another thread, I have managed to isolate it and the closest thing I have found is what is proposed in this thread. My 301 starts well when cold and starts well when hot. After doing several tests, regulating idle speed, restarting the ecu, checking possible engine air intakes, air filter... I have managed to detect the following: I start the bike and after having adjusted the idle speed to around 1800 rpm, I let the bike warm up at idle until the first fan starts. I start using the motorcycle and it runs perfectly, the fan activates in alternating cycles with rest. But always, after 30 minutes of using the motorcycle, the revolutions begin to drop and fluctuate when you release the gas. When this happens, it lets out a sputter through the exhaust as if there were an ignition problem. If it accelerates it works perfectly until you release the gas and this malfunction begins. When it gets to this point it smells a lot like gasoline and the fan never stops. If you stop the engine, it starts fine again but starts failing again. The engine is allowed to cool for at least an hour and both the engine and the fan return to normal operation until about 20 or 30 minutes pass again, at which point it begins to fail again. I don't understand what's happening. I think that something electrical fails when it reaches a high enough temperature but I can't detect what it is.

[on it]

6 hours ago, IBA4rt said:

I recovered the post although I considered my problem solved after changing the fuel, which I had published in another thread, I have managed to isolate it and the closest thing I have found is what is proposed in this thread. My 301 starts well when cold and starts well when hot. After doing several tests, regulating idle speed, restarting the ecu, checking possible engine air intakes, air filter... I have managed to detect the following: I start the bike and after having adjusted the idle speed to around 1800 rpm, I let the bike warm up at idle until the first fan starts. I start using the motorcycle and it runs perfectly, the fan activates in alternating cycles with rest. But always, after 30 minutes of using the motorcycle, the revolutions begin to drop and fluctuate when you release the gas. When this happens, it lets out a sputter through the exhaust as if there were an ignition problem. If it accelerates it works perfectly until you release the gas and this malfunction begins. When it gets to this point it smells a lot like gasoline and the fan never stops. If you stop the engine, it starts fine again but starts failing again. The engine is allowed to cool for at least an hour and both the engine and the fan return to normal operation until about 20 or 30 minutes pass again, at which point it begins to fail again. I don't understand what's happening. I think that something electrical fails when it reaches a high enough temperature but I can't detect what it is.

ive found that a faulty temp sender in radiator  causes this fault    as the sender is not just the sender its also the choke .A faulty one puts choke on/off  at will . The feel you get riding the bike is the motor dose something different to what your doing to the throttle hope this helps

[IBA4rt]

40 minutes ago, on it said:

He descubierto que un sensor de temperatura defectuoso en el radiador provoca esta falla, ya que el sensor no es solo el sensor, sino también el estrangulador. Un sensor defectuoso activa y desactiva el estrangulador a voluntad. La sensación que se obtiene al conducir la motocicleta es que el motor hace algo diferente a lo que se hace con el acelerador. Espero que esto ayude.

good morning. thanks for answering. I don't understand what you mean when you say that it acts as a choke. Could you expand a little more information? When the motorcycle makes these explosions and the idle fails, I notice a lot of gasoline smell, so I don't understand what you mean by that choke function of the temperature sensor, but it could be related since when the motorcycle fails the common pattern is that the fan never stops and the engine temperature, however, is normal because I have measured it. I mean there is no over temperature.

[on it]

23 minutes ago, IBA4rt said:

good morning. thanks for answering. I don't understand what you mean when you say that it acts as a choke. Could you expand a little more information? When the motorcycle makes these explosions and the idle fails, I notice a lot of gasoline smell, so I don't understand what you mean by that choke function of the temperature sensor, but it could be related since when the motorcycle fails the common pattern is that the fan never stops and the engine temperature, however, is normal because I have measured it. I mean there is no over temperature.

 

23 minutes ago, IBA4rt said:

good morning. thanks for answering. I don't understand what you mean when you say that it acts as a choke. Could you expand a little more information? When the motorcycle makes these explosions and the idle fails, I notice a lot of gasoline smell, so I don't understand what you mean by that choke function of the temperature sensor, but it could be related since when the motorcycle fails the common pattern is that the fan never stops and the engine temperature, however, is normal because I have measured it. I mean there is no over temperature.

there is no physical choke on the bike  so the  temp sender has a bimetallic strip  that sends signal to ecu  to make fuelling richer for cold starting and a signal to the fan relay...... then once hot  normal fuelling takes over   ( thats why  it best to let them warm up before riding ) so when the temp sender fails it sends a false signal to the ecu causing  the ecu fuelling to be out of sink with throttle setting ie twist grip + butterfly 

[IBA4rt]

9 minutes ago, on it said:

 

no hay un estrangulador físico en la motocicleta, por lo que el sensor de temperatura tiene una tira bimetálica que envía una señal a la ecu para enriquecer el combustible para el arranque en frío y una señal al relé del ventilador... luego, una vez que está caliente, el combustible normal toma el control (es por eso que es mejor dejar que se calienten antes de conducir), por lo que cuando el sensor de temperatura falla, envía una señal falsa a la ecu, lo que hace que el combustible de la ecu esté fuera de sumidero con la configuración del acelerador, es decir, puño giratorio + mariposa 

Now I understand it, because it makes perfect sense. I understand that the sensor (since I don't have another one to test) if I measure the resistance as specified in the manual, I can know if it is defective, right? Can you think of another test to find out if that is the fault without changing the sensor for another one? thank you very much for helping me.

[on it]

2 hours ago, IBA4rt said:

Now I understand it, because it makes perfect sense. I understand that the sensor (since I don't have another one to test) if I measure the resistance as specified in the manual, I can know if it is defective, right? Can you think of another test to find out if that is the fault without changing the sensor for another one? thank you very much for helping me.

im sorry i dont  have any test info on what to do   i just change them i know thats not the best way to fix or fault find  but as i keep most electrical items on hand saves time and ease ,

as i say its more than just a fan switch  that is why you can not short it out like beta gas gas ect   to run the fan  if it fails 

 

Edited Friday at 02:34 PM by on it
add

[lemur]

I always buy trials bikes in pairs and have no problem keeping at least one of them running, you need that second bike to 100% identify a sporadic failing component, that's how a dealer would fix it and keep the service cost reasonable, just swap assemblies until the problem goes to the other bike and now you know what parts to order.

[IBA4rt]

Well, although I haven't tried it yet, I have no words to thank you for the approach you have given me. Apart from having all the logic, I just picked up the manual and it specifies how to check the sensor from the control unit connector. I have tested all the parameters in this panel with a tester and more or less all of them correspond to the parameters except the temperature sensor that, by placing the tester on the pins indicated on the connector, does not return any data, there is no resistance or continuity. I have checked the sensor connector itself and everything looks normal, so one of two, either I have a sensor failure or I have a failure in the electrical installation since the formal way to check it is not in the sensor (from which, by the way, three cables come out, no only two).

[IBA4rt]

On the other hand, I wonder how a defective sensor or installation can be on a completely new motorcycle.

😤🥴