Effect of humidity and air temperature on carb performance

[drunkmunkey6969]

I'll drop the pilot and see how it goes

I'd leave that to Joan Armatrading.

[tony]

bloody ell yer confusing me now!
Is it running rough at mo? Does the bike sort of die when you open the throttle?

Generally, it's running fine. It's just too bloody cold at the moment to do another series of plug chops .

When it's damp, moist air it dies somewhere on the pilot. You pull the clutch, drop the revs and then rev it whilst letting the clutch out and it sort of clears. The carb has a RamAir through the panel. It only does this on damp days. Conversely, when it's cold and not damp, performance is so much better than usual.

ah ok. what carb spec etc? I would check air screw then maybe drop as you said. Forget plug chopping to check lo end running. In my experience plug chops only really indicate when flat out as the oil doesnt tend to burn off too well at low rpms/ throttle openings and its hard to see. A good dyno operator could help better to sort this once and for all.
If all that is no good ask Joan

[storkfoot]

Cheers, Tony. I'll try the air screw tomorrow and may be flick the choke on when it bogs/dies to see what happens. Thanks again

[byron]

turning in my airscrew ¼ turn [on a VHSA, so making it richer] improved the low revs pulling away today. I didn't have to rev and slip the clutch at lights like some kind of boy racer. but it's not quite so cold today, and is a bit damp out there

[RICSPEED]

I'll drop the pilot and see how it goes

I'd leave that to Joan Armatrading.

you'll have to explain that one to me Dan

[coaster]

Cheers, Tony. I'll try the air screw tomorrow and may be flick the choke on when it bogs/dies to see what happens. Thanks again

That's what I would have thought, it makes sense that you would need a richer mixture if its cold, thats why you need the choke

My 185 muggy actually runs better in damp conditions but then my flter is under the panel and not stuck out in the rain, could tha be a factor?

colin

[sean brady scooters]

if its damper,it is usually also colder.............so that would make it feel better,coupled with the fact that your filter is not stuck out in the rain and getting water on............

[sean brady scooters]

internal combustion engines are essentially air pumps............
and in order to run at peak efficiency,they depend on a specific ratio of air mixed with fuel.
In turn,the HP and torque available depends on the density of that air............
Higher density means more oxygen molecules are available for combustion,and hence more power............
Lower air density means less oxygen and less power...........
AND SO MOVING ON..............

HUMIDITY................
humidity ....is water vapour,..........
In a given amount of air it displaces oxygen content ,making the air less dense,as a result the engine takes in less oxygen ,and its output is reduced.
for eg,......on a hot day at sea level high humidity would cause a scoot to run rich.........


PRESSURE............
Barometric pressure influences the intake charge density and flow through an engine.

If talking about climate...........not altitude..........air temp has the greatest effect.........
the warmer the air is ,the less dense,........less oxygen.......= less power.

The difference in performance between say a winter day and summer day can be at least 10%
.....if both humidity and barometric pressure remain constant...........
change those parameters,and the difference can be SO much more.........

The key thing to remember ,however,is that temp,humidity and barometric pressure are rarely constant.
And though the performance changes may be slight,this explains why your scoot will perform at different levels at different times of the hour,day,month and year.........

even though ALTITUDE is a matter of geography ,not weather,Elevation plays a big role in the
HP/performance equation.........
for every 1000 feet you climb above sea level,there is a reduction in air density of approx 4.5% ...........and so a corrosponding loss in HP.........
(in fact.........just for a matter of interest,here in north yorks we are on average about 1000 ft above sea level)

MAX performance from a scoot will always be at sea level,when the air is cold and dry and theres a big ridge of high pressure above you...........
on the other hand...........worst performance would be at high altitude,on a hot ,humid day when barometric pressure is very low.............................

also ,.........would just like to add the fact,that no matter how well you think your scoots been set up /dyno,d etc .........
you should realize ,that on just one rally alone you could possibly encounter all the above conditions.............or many of them..............even in one day................

[firekdp]

That's what I would have thought, it makes sense that you would need a richer mixture if its cold, thats why you need the choke
colin

Choke is needed when the engine is cold because a slow cranking speed with resulting poor airflow will cause poor atomisation of the fuel, also no heat is present in the inlet manifold or cylinder head to assist in fuel vaporisation. Much of the fuel will condense on the cold inlet manifold walls so the mixture must be enriched for the engine to run properly until warm.

[weller51]

I'll drop the pilot and see how it goes

I'd leave that to Joan Armatrading.

ah,im glad to see there will be banter on here !!!!!!(crap song tho)