Effect of humidity and air temperature on carb performance

[storkfoot]

Just before the Winter kicked in, I roughly set my carb with a couple of plug chops, and a couple of flicks of the choke___nowt too scientific then!

Anyway the plug colour seemed fine to me and it ran pretty well throughout the range, although during the Winter I only tend to do 6 mile trips to work including a quick blast down the dual carriageway if I'm lucky. I know that before I go any distance over about couple of miles at high speed, I need to properly check the plug colour of the main jet.

In the last few weeks I've noticed that the scoot (186 Mugello; PM25; bgm keihin PWK28) really likes cold, non-damp, air. I've also noticed that it bogs a bit when it's rainy and damp.

I just want to get my head round what's happening. I think the jetting at pilot and/or needle is just a tiny bit rich as:

> when the air gets saturated with water, there's less air molecules and, therefore, more petrol ie. too rich.

> when it gets cold, but not damp, there are more air molecules making it a bit leaner___this is what my Muggello likes.

So, the conclusion is that I'm just a bit too rich Does this make sense

Paul

[Dazza]

Don't know why but I know that fuel combusts more efficiently with cold air - not much help eh?

[tony]

Cold air is denser - so in effect you are getting more in. If the scoot was set up at say 25c it will require richening up i the air temp drops a lot to get the air fuel ratio right.

[sean brady scooters]

and dont forget ........it will then need re setting come summer again.........
best to find a compromise setting.........that works good all year round..........
it may not be the optimum .......but should be good for a road scoot ridden all year .....

[RinB]

Oh no dont do it

Start talking about this well get into plants in the morning with dew ect ect

[sean brady scooters]

156 d will be along shortly to put you right on this.......................

[RinB]

[byron]

hmmm... maybe that's why mine needs a bit more throttle pulling away these cold mornings, even once it's warmed up. perhaps I'll just turn the airscrew in a fraction.

[T5-190]

It has often been noted that things like race tuned cars and bikes go a little better when it is a cold crisp morning. I know that Mikuni and Dellorto both do a sliding chart showing which way to go for the jets. Same thing for alltitude.

[156 D]

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