Carburettor Icing

[bmews]

Do K engines suffer from Carb icing. I have noticed since the weather got cooler here in Sydney that the beast stalls soon after driving off in the morning. Today with rain it stalled many times until it got really hot.

 

Should I use the winter setting on the stock air cleaner?

Edited May 17, 2005 by bmews

[bmews]

Thanks, that confirms my suspicions. I had this trouble really bad once before in a Cessna and caused me an emergency landing.

[Super Jamie]

running the stock carb, you usually have to tune your idle mixture and speed at least twice a year to compensate for temperature changes

[Medicine_Man]

My motor takes a few minutes to warm up in the mornings now its getting colder, once it hits the first mark on the temperature guage its usually ok..

[bmews]

Thankyou once again.

I presume one winds in (leans) the screw until it runs roughly and then richen a turn or two?

Barry

[bmews]

Mr Grim,

Indeed it was grim for a while but don't worry about the flying, I just got caught in a bad situation when quite inexperienced. We were flying low on a rally spotting object to answer questions etc etc. 500ft above ground under cloud and kept opening the throttle to maintain power.

When the throttle was fully opened I realised there was probably icing. Now applying full carb heat to an significant ice load causes a big power loss for a few minutes while the ice melts and as we were already low we had a problem didn't we and those trees looks very tall so I quickly put it down on an old ag strip.

 

It ran normally later offcourse, and I went home tail between legs.

[Super Jamie]

if you search here, toymods, and oldcorollas you can find my idle tuning howto. ideally you should tune for best vacuum at idle. i run really rich idle because i don't use a choke

[reCOUPErator]

Whats the winter setting?

[Super Jamie]

copypaste of my post from toyfags:

 

you just need to find out wether or not it's a fuel bleed (in is leaner, out is richer) or an air bleed (in is richer, out is leaner)

 

get a notepad and make some columns. idle speed, idle mix, result. now, using a screwdriver (or 5c piece if it's hard to get a screwdriver in there) wind the idle mix screw all the way in and count the turns. then bring it back to where it was (count the turns out), just so you know how far it is out to start with

 

now adjust things, make precise half turns of the screws. write down everything you do, and what changes it makes to the engine. this way, you can go back to settings that worked if you stuff up

 

your table should look something like this

 

SPEED - MIX - RESULT

--------------------

3 out - 0 - stalls

4 out - 0 - stalls

5 out - 0 - idles 1200rpm

5 out - 0.5 in - idles 1100rpm

5 out - 1 in - idles 1000rpm

 

and so on. those are totally unrealstic numbers, but you get the idea. tune in full turns, then in half turns, then in quarter turns. once you have two quarter turns between which your settings are good, tune by hand

 

if you have a vac gauge, you'll be able to get the car idling at many different states of throttle and mixture, you should try to achieve the idle with the highest manifold vacuum, something like 18in/Hg is good for a stock motor. anything under 15in/Hg is a pretty crappy idle, and it will use alot of petrol

 

alot of service manuals will tell you to tune to "best lean idle", where you raise the rpm, lean out the idle mix, then lower the rpm, lean out the mix, etc - till you get a factory rpm idle with the leanest possible fuel delivery

 

i personally don't like this, as the idle circuit of the carb affects your fuel delivery right up till about 2500rpm, and you want a bit of fuel in there to make power, and make the car go smoothly, more than the minimum anyway. i also tend to run a rich idle because i don't use a choke in my cars

 

ps. you should always tune the car at operating temperature

Edited May 17, 2005 by Super Jamie

[mikeys toy[RL]]

wtf; it's getting COLDER down there??

[Jason]

Yep, going into winter :)

[coln72]

My old KE35 (5K, 3KB carbies) used to ice up regulary between Melbourne and Ballarat - no matter what time of the year. Really any long continuous running at constant throttle would set it off.

 

Ended up having to run tubing off the extractors into the aircleaner housing as it didn't have a winter setting. Also found that running a small amount of octane booster helped mionimise the problem.

 

PS. it was well below ten degrees down here :)

[bmews]

Thanks all.

Changed to winter setting, problem sorted.