kj1074

has anyone experienced carb icing issues with the stock Aisan carb? ive heard that even though its above freezing temps the carb can still ice from the accelerated spead of air through the carb. im having hard start problems this winter. i run a manual choke and no matter where i set it i have problems keeping it running until it gets at least a little warm. i have to let it fire with the choke closed then open it and keep my foot in it for about 30sec. all this at only 40 degrees! any advice would be greatly appreciated.

84sr5yoty

Sounds like the carb is running too lean for one reason or another like vacuum leaks or improper mixture adjustments.

It would be worth trying some moisture removing additive that you dump down your gas tank. It's available at any automotive parts store.

kj1074

good thought on running lean, i just assumed 2.5 turns out is ok with an open exhaust and open intake.

fredbauer

Hi , I had the same problem with my 81. Cured mine by taking off the snorkel that ran from the front and made sure it could get warm air from the headers. I also put a half sheet of cardboard in the radiator and made sure the heater hose connections that ran to the carb were burped . Haven't had any problems since. Fred

kj1074

yea mines set up the same way, great minds think alike. but my problem is more initial start up when there is no heat available; after about the 3rd try it fires but will only stay running if i turn off the choke and keep my foot in it, only takes about 20-45 sec before i can let it idle and its fine. thanks!

rowdy235

my carb is icing up as well, but its around 23* here. I'm missing the heat shield on the manifold for the HAI, as well the hose isn't hooked up. Tomorrow I'm off to the junkyard to get one.

kj1074

see i could understand icing in the 20s but not in the 40s. i think i f uped my carb. when you close the choke shouldnt it idle higher and not kill it? i may be a little confused on how the top butterflys work. the passenger side one is choke only and the driver side butterfly does what? on mine it doesnt do crap, i would assume it would open with the secondary. am i wrong?

rowdy235

Yes the top plate drivers side opens with the secondary barrel.

Tomorrow i'll have a working HAI so hopefully no more icing.

TrikeKid

Throw some Heet in the tank the next time you fill up, that's what I have to do with my Weber. I can't run a HAI with the current air cleaner. Mine will start fine on the electric choke, but I usually have to slap it into neutral and brake with the left foot, gas with the right to keep it running.

82yota

Carb Icing is most common above freezing and up to 60-70*F. It isn't common below freezing as the air is too cold to hold much moisture but when you are sucking so much air through the venturies in the carb it will form ice. This is a common problem on aircraft. Thats why they have a carb heat knob on them. You always pull the carb heat on when landing to make sure there is no ice in the carb if you need to add power fast. I never used to use it in my cub but coming in for a landing this fall when it was around 45* or so I needed a bit of power on landing and I gave it throttle but the engine almost died so I pulled the carb heat on fast and saved it from dying. I was already on the ground but didn't want to get out to start the motor again as mine has no generating system and no starter. Get that heat shield and hose on and your problems should go away. Had the same thing on my 82 after I put my header on but I was able to fit the stock heat shield around the header with a bit of trimming and works well now.

kj1074

yea that makes sense, the airplane analogy is great. i was talkin with an old mechanic the other day and he pretty much told me the same thing that carb icing usualy wont happen in sub freezing temps because of the lack of humidity. it wont be cold here much longer anyways, it was 38 last night and today it is almost 70! gotta love central Texas. very salubrious.

Nickle Eye

I was having icing problems too when temps were in single digits. I pour a little sea foam in carb while running. Put some in the tank also. You'll have to have one hand on linkage to prevent it from stalling. It cleared it right up. The stuff is available at most part stores. I swear by it. Found out about it on a mortorcycle forum I'm on.

87blyota

hate reviving a old topic but its in the mid to low 20's with 86% humidity and I just started having carb issues when this cold spell came through does anyone think it may be carb icing?

millball

In the mid to low 20s even 86% humidity does'nt allow the air to hold much water, so no, carb icing is probably not your issue. Poor fuel vaporization might be, or ice in the fuel bowl.

I think that there may be confusion as to what carburetor icing really is.

It is NOT frozen water in the fuel. Ice in the carb bowl, or in the fuel lines can surely cause problems, but carb icing is something entirely different.

Carburetor icing occurs, usually in fairly damp, relatively warm (40s, 50s, even into the 60s, temps when cruising at relatively lo partial throttle, where there is high manifold vacuum.
The venturi effect in the carb throat (expansion causes cooling) coupled with the rapid evaporation of fuel in high vacuum conditions, turns the carb into a mini-freezer that freezes the moisture entrained in the intake air as it passes thru the carb, depositing a layer of ice in the carb venturis. This causes the intake fuel and air to become less and less as the icing progresses.
I have seen old VW air-cooleds actually overheat from excessively lean mixture and stall when hiway cruising in very damp conditions in 50-55 degree temps. All caused by carb icing.
Some 60s and 70s ford V-8s had a plate under their carbs that provided hot water heat to help prevent carb icing.
I added a heater control valve to this circuit on my '72 390 pickup, so I could cut off this heat during hot weather, because it caused hard hot starts when the gas in the carb would boil.