Cold fouling spark plugs?

[Redrider]

Im starting to figure that I am doing something wrong when I start my bike(s) in the winter. Ive never fouled a plug on the trail with either of my bikes 99 cr 250 and 04 yz 250. I used to fould about 6 plugs a year on my cr only on start up in cold weather I thought that it must just be the crummy cr 250 jetting. Even recently on my yz, I foulded a plug again in start up in cold weather and this thing has never fouled a plug. Is it me or is that just part of the cold weather routine. On the yz, I left the fuel on overnight and pulled the bike along a rough 10 mile dirt road so I figured I may have merely flooded the bike with all the bouncing etc :think: . Any advice appreciated.

Redrider

 

[uts]

When the weather turns cold fuel doesn't vapourize as easily. So instead of vapour you get little droplets which are wet fouling your plug. Many would say you need to re jet your bike, which is fair for the pros, but there are a few things you can try first, before pulling anything apart.
1. Make sure you turn the choke off as soon as the bike starts.
2. Keep the revs up a bit higher than idle for the first 30 seconds. Don't pin it of course. You will probably hear it trying to foul, then it will start to fire correctly.
3. You could take the air screw out a bit to lean the pilot circuit. But if it affects throttle response, turn it back.

My Bike likes to wet foul on warm up too, but if I follow these steps it doesn't fail.

 

[mtk]

Cold air is more dense than warm air, therefore you don't need to lean it out at all, but rather richen the mixture in winter.

 

[DWreck]

I went through this for years with my KX. Finally tried a smaller pilot, six months later I'm on the same plug. I could kick myself for not doing this sooner. Its cheap and easy to change back if it doesn't work.

 

[pace]

Cold air is more dense than warm air, therefore you don't need to lean it out at all, but rather richen the mixture in winter.

This is true, but it is also true that fuel does not atomize well in extremely cold temperatures - leading to cold fouling, which will be exacerbated by richening of the slow circuit. It's a bit of a 'gotcha' situation..

Warming the cylinder can help cold starting immensely..

-pace

 

[Oldschooldeathwish]

put in a hotter plug that should help it burn off most of the excess fuel when it is colder