Carb Icing Explained

[HOG maniac]

How does it stop it ? Carb heater ?

[Tooty]

The bottom line is, yes, a carb heater will stop it. Almost all carbs on aircraft have some sort of carb heater. Some use a water jacket from the radiator but air cooled motors have some form of air ducting to direct hot air over the carb.

Here is an interesting story for you. When we were leaving the Bartjest Rally back in March, the six carb equipped bikes in the group all suffered rough running while the guys were sat with the bikes ticking over ready to leave. My own Dyna with its S&S motor and carb was the same. It started OK but when I took the choke off it ran like a bastard until I'd done a fair few miles. The conditions at the Tan Hill Inn that Sunday morning were ideal for carb icing, i.e. just above freezing, fog/mist, bikes left running at a low throttle setting for a long period. Needless to say, the EFi bikes in the group were completely unaffected.
A lot of postings suggest fuel additives as a solution but this will only stop the petrol freezing. CARB ICING forms from the MOISTURE IN THE AIR going into the carb. Petrol additives will have no effect on the air entering the carb.
Some carbs work better than others and the concensus is that Mikunis are the least prone to carb icing.
Bikes fitted with the Rivera Dual Runner manifolds or similar extended manifolds suffer badly from carb icing. You can actually see the condensation forming on the outside of the manifold even on a hot day and despite the motor being hot, the manifold will be cool to the touch. This is because the low pressure zone in the manifold leads to a drop in temperature. Basic 'O' level Physics.
This posting isn't an attempt to fix carb icing, it's just me saying DON'T PANIC if it happens to you occassionally. It's as natural as Middle Age Baldness.

Regards

Tooty

[HOG maniac]

Does this cause the jets to block up with ice and the bike run lean. Or does the slide ice up causing the bike to run rich.

[Baff]

At the risk of resurrecting an old thread and maybe pissin' a few people off, my beastie has dual Qwiksilver carbs, and the carb to head measurement is damn near 12" (no jokes about finally having got the length I've always dreamed of, please). On anything but the warmest of days, there's condensation on the manifolds. Only on really cold days does it have much effect, thank God, but I often think about it when I feel my knee getting cold.

Baff

[HarleyDuc]

Apparently some of the temperature drop is caused by fuel evaporating which adds to the effect of low pressure in the venturi. Additives to the fuel will reduce this element so I guess thats why there is an improvement with FST Pro and Isopropyl Alchohol etc

[HOG maniac]

Since posting I have learned that a fuel additive is the way forward.

[HOG maniac]

From the web:

Pro-FST (Fuel System Treatment) was developed in 1992 following an unofficial request from Kawasaki Motors (UK) Ltd., for something that would deal with the particularly British problem of carburettor icing in damp, cold weather. (It was also specifically a motorcycle malady