Topic: Cold starts and... cold starts

[Deltarider]

Coming days there's ample time to overthink things. Here's something, I have never understood. My bike fires up immediately when I have rode it the day before. Even two, three or four days later, I only have to point my finger at the button and it starts rightaway. It takes longer however when it has been a week or more. Why is this? I've tried to find out myself by:
A. Charging the battery to its maximum prior to starting.
B. Draining the floatbowls and refill it with fresh gasoline, again right before starting.
Nor A nor B makes a difference. What's causing this difference in cold starts?
Merry Cnristmas and wonderful moments of enlightment!

[Tomshep]

Oil drag and reduced clearances, for one thing and low temperature reducing the ability of the battery to supply current for another. Damp air contains less oxygen so humidity can play its part, too.

[jlh3rd]

Oil drag and reduced clearances, for one thing and low temperature reducing the ability of the battery to supply current for another. Damp air contains less oxygen so humidity can play its part, too.

he charged his battery. Damp air doesn't matter, it's the length of time between starts . Mine does this also....curious...

[DaveBarbier]

Fuel still in combustion chambers from when it was shut off. If left a long time it’ll dissipate so you’re starting with a dry chamber. After 24 hours there will still be wet fuel and some vapors to help start it up.




This is completely out of my ass but it sounds right and if I didn’t add this sentence people might think I know what I’m talking about.

[Henning]

Fuel still in combustion chambers from when it was shut off. If left a long time it’ll dissipate so you’re starting with a dry chamber. After 24 hours there will still be wet fuel and some vapors to help start it up.

Agree with this, and yes, mine has the same "issue", can be tricky to start if it has sat more than a few days. It helps to give it a big handful of throttle. Back when I was a kid in the sixties, it was common to blip the throttle and cut the ignition when parking your car. The idea was to pump fuel into the cylinders to help startup the next day.

[Scott S]

 My latest 550 build sometimes takes a minute for #3 to catch. Can't tell you why. Carbs are super clean,  ignition isn't a factor or #1 would drop...
 ...it's weird.  When it catches, it runs great....normal.... but for whatever reason,  #3 is slow sometimes.

[Kevin D]

This is completely out of my ass but it sounds right and if I didn’t add this sentence people might think I know what I’m talking about.

ROFLMAO!

[dave500]

residual fuel in intake tracts?funny how I can assemble an engine and it fires right up.

[PeWe]

My stock CB750 K2 has same issue. It need full choke and start in a rich cloud thru the pipes when it has been resting for a week.
I have not get used to it yet. Ign off and let it go on starter with full choke for 5 sec. Ign on with less choke 3/4- 1/2  and start it.

[Tomshep]

Of course cylinder 3 can take time to start while 1 is fine for a number of reasons. Dud plug cap, dud plug, partial short from HT lead to ground and that's just three of the ignition causes. Valve sealing, blocked idle jet, inlet air leak. Rule some out with a compression test but it still could be ignition.

[rotortiller]

What I have found is if the bike sits and it is cold out it may be difficult to start on the electric starter with full choke. If you use the kick starter it normally fires right up cold . Pretty standard for type even when new back inn the 70s. Old bikes were not designed to be snowmobiles however using the 77/78 throttle as a primer pump (accelerator pump) will make for an easier cold weather start.

The tasked starter in a cold situation pulls  energy away from the spark plugs for igniting the fuel plus the kick starter will provide higher starting compression. It's -7C today and my bike has been sitting in the shed for a month, because I know the electric starter will not be ideal  I'd kick start it rather than beating up the battery. Remember cold oil congeals adding friction and cold battery performance is less, fuel does not atomize as well; if it sits for weeks a less than ideal battery may self discharge some.

[PeWe]

Deltarider, have you tried starter gas on rattle can?
Spray inside the airbox, hit the starter, if not fire up direct it is not the fuel supply.
Check if ignition is alive. I usually use an extra plug.

[Deltarider]

Deltarider, have you tried starter gas on rattle can?
Spray inside the airbox, hit the starter, if not fire up direct it is not the fuel supply.
Check if ignition is alive. I usually use an extra plug.

No, because there is no problem. Cold start within 4 days after last ride, happens immediately, within a second, cold start after a week happens within 4 seconds, so no big thing. I was only interested in the 'why' of the phenomenon.

[Tomshep]

Yes, oil drag, partial evaporation of the more volatile fractions of the fuel in the float bowls  and battery droop.

[Deltarider]

Yes, oil drag, partial evaporation of the more volatile fractions of the fuel in the float bowls  and battery droop.

But... partial evaporation of the more volatile fractions of the fuel in the float bowls and battery droop were ruled out by me, as you can read in my opening post. Also evaparation of left mixture in the combustion chambers, is not very convincing, given the rpm the starting motor lets the engine spin rightaway. I mean fresh mixture will arrive in the combustion chambers within a fraction of a second. Oil drag? But... oil after just one day is as cold as after a week. I'm sorry, but I have not read the answer yet. Intriguing, isn't it? I was thinking maybe left over mixture in the combustion chambers will deposit more on the plugs noses in a period of days. So I could do this experiment: after a ride, have the engine spin without any fuel arriving there, so the combustion chambers will be dry and then do a cold start after a week. This will not happen before next spring, I'm afraid.

[dave500]

its the same as rolling out of bed after a sleep in?i cant be #$%*ed at first,then ok if I have to?