650 twin spark - tough starting the morning after

[Craig380]

Originally Posted by embee

I know my (old) Yaris can suffer from this if I start it when just part warm and stop it again, the next cold start can be a pig.

A lot of cars get this, especially those with hydraulic tappets. The tappets can pump up and keep the valves off their seats, so there's not very much compression when trying to restart. My old Mondeo did it.

It's called 'lawnmower syndrome' (people starting their cars so they can get the lawnmower out of the garage)

[aesmith]

Cheers. I'm surprised that a couple of weeks out of use is long enough to require special handling before startup. My bike's normally used every weekday, but is out of use for a couple of weeks at a time when we're off work, or most recently because our track was impassible.

The plug fouling theory sounds plausible. I would have though over fueling would have dispersed overnight.

So the question is how warm is warm enough to avoid these issues? Typically it would arise for me if the bike needs to be moved from the shed to the garage and I can't face pushing it up the slope. Or running a few minutes to check the Scottoiler is working.

Hope the answer isn't "until the fan runs", I don't think I've ever got the bike that hot either in the shop or when riding.

[embee]

If you do get soft carbon build up on the plugs it will "dry" but it's like a sponge so as soon as it next fires up from cold it soaks up the condensation and is way more prone to foul. To self clean effectively the plugs need to be up to something like 300C and running in a non-rich mixture regime, best achieved by allowing the engine to warm for at least a couple of minutes then holding the speed steady at around 3000rpm typically for another 30sec or so. That should be enough to be sure of avoiding repeated cold foul issues. It's not the rich fuelling per se, although that is what produces the carbon/soot, but the condensation of the water from combustion mixed with the soot which is the problem.

With any modern engine it is usually best practice to do starts "un-assisted", i.e. don't touch the throttle, and wait for something like 10sec after starting before using the throttle at all. Sure it isn't always essential, but that's usually the best way to avoid issues.
No need to run it until the fan starts, just until the plugs are hot enough, and rpm is the primary factor here.