Talk Morgan Forums Morgan Sports Cars Morgan Three Wheeler & Super 3 Engine not returning to idle

Hi Morganeers,
I know there is a long and exhausting thread on this topic ( https://www.talkmorgan.com/ubbthreads.php/topics/757598/1 ) but I wanted to make my own long and exhausting post on my recent experiences.
I have had three instances of my M3W not returning to idle after accelerating and I have come to the conclusion that it was the injectors potentially being contaminated that was causing the problem.
I run 98 octane fuel which in Australia is sold as a premium fuel with various additives including a fuel system cleaner.

Typically the engine would remain at high rpm for a few seconds and then decay to idle at a slow and steady rate.
This time I also noted that it would start to decay and then all of a sudden, drop back to idle. Imagine the sound of a poppet type valve suddenly closing and RPM dropping rapidly.
Now there are not many springs in the fuel system and I had thoroughly checked the throttle cable and found nothing out of the ordinary.
Now this comes at the same time that Australian authorities had removed some of the fuel quality control provisions in order to deal with the lack of fuel availability caused by the current USA/Iran war.
A friend who races bikes has said that the 98 octane fuel has been terrible of late and it got me thinking that the fuel injectors (which typically utilise springs in their operation as a return mechanism for the pintle) could be affected by dirty fuel.
I put a bottle of fuel system cleaner in a full tank and after about 90km, all trace of sticking at high RPM has disappeared.

I suspect that with an injector sticking partially open, even with the reduced throttle position, additional fuel could be leading to the high rpm I was experiencing.

I hope that makes sense (and not too long and exhausting topic as I thought it might be)
Cheers,
Paul

I routinely add some fuel system cleaner to the petrol every year and I have an inline fuel filter before the injectors, unlike the standard system. I may have been lucky but I get few fuel related problems. Hanging idle speed has been caused by the wheel speed sensor or idle air control valve not working correctly as well.

An engine reluctantly returning to idle is more likely to be running lean, than rich. So too much air, or not enough fuel.

Echoing planenut, I would suggest the issue to more likely be associated with the idle control valve.

Just to be a pain... I would take a good look at the accelerator pedal and the springs attached to it. I had one break and it fitfully returned to idle in its own sweet time.

I am happy with the throttle cable and cleaning and checking the functionality of the air idle control valve made no difference. It was the rapid drop in RPM on a few occasions that made me think that something spring related was involved. Mechanical issues rarely fix themselves. So I am suspecting a build up of gunk that may have been an issue. I would like to have a supply line filter though. Is there a recommended setup? Something that won't affect supply pressure and flow rate?

Check out this THREAD for some ideas. I use a Bosch F5316 (0450905316) filter which is compact and has the same push-fit type fittings as the standard filter/regulator.