Stalling issue 906

[hardo]

Dear all

My 1989 Ducati Paso 906 runs for about 20 minutes without any problems and then cuts out whilst riding; first it loses power, then it stops completely. After a 5-minute break, it starts up again and runs for another 10 to 20 minutes, and so on. What could be causing this? The fuel tank vent is working perfectly.

Some background: The Ducati has recently undergone a service with all wear parts replaced, and the carburettors have been cleaned. It also has a new fuel pump (a new diaphragm-controlled unit from Japan to replace the old one - Yamaha TDM 850 Year 91-96 Part No.: 4BR-13910-09-00); it is not the electric type that was originally fitted. I suspect this is the source of the problem. Is it a pure thermal issue? How would you go about troubleshooting this?

Many thanks, Hans

[nickta]

Hi Hans.
Do you still have the original pump?
Cheers.
Nick.

[Mc tool]

Carburettors ...you have two? If it stops as opposed to running on one pot you'd have to think it was something common to both ....so you might be on the right track looking at the vacuum fuel pump , but why would it stop after 20 mins and work again after a rest ( sounds more Australian than Swiss ) . I guess the 1st thing I would do is to confirm that there is spark , ( one of the Temu spark testers will do that job for 8 bucks) before getting to suss of the fuel pump. Weirder things have happened but you might check that either the fuel or the vacuum hose isnt being kinked as things warm up .
Lemmie know how you get on

[hardo]

Thanks al lot for your feedback. I’ll have a look. It’s possible that the pump or the fuel hoses are too close to the engine, because the problem does sort itself out once the bike cools down again. I’ve still got the old electric pump, but the garage said it was on the way out and therefore recommended replacing it (perhaps a mistake). The sparks have just been replaced, but I will check. I’ll keep you updated. Best, Hans

[Mc tool]

Hi Hans , when things start to work again after a cool down it often turns out to be electrical . Some components will fail as they get hot and work again when cool .....which is why I suggested to check for spark as soon as it stops .
When the motor stops does anything else stop working , like maybe the blinkers ? Im just thinking that it might be a low voltage thing ....bad connection gets hot ....resistance goes up volts go down .....the Weber marelli ignition unit will play up if it is getting only 10v or less ( ask me how I know )
Just re-reading you 1st post , has the vacuum fuel pump only just been fitted ? The pump itself will be up to the job , but the fitting might be the issue . Where is the vacuum line attached to the motor ?
Hamish

[hardo]

Thank you Hamish!

The battery is new and fully charged. Everything’s working fine, so to me it didn’t really point to an electrical problem - also because the motorbike first loses power, then runs on just one cylinder for a very short while, and then won’t start again for 5 mins. The first time it breaks down lasts 20 to 30 mins, as the bike starts when cold; after that, the cycles are only 10 mins long...

Yes, the fuel pump has just been fitted as new by the garage. I’ll take the fairing off, have a look for any kinks or similar issues, and if necessary take some photos and post them here. Of course, I’ll need to keep an eye out for other possible causes too; I’d be particularly concerned about that old-school electronic control unit under the seat – they do tend to give up the ghost from time to time ....

Sure I will look for the plugs too and the tank venting (which would be easy to verify). Best, Hans