Will a new air filter cure carb icing?
Q. I have had no problems with my 2005 Suzuki GSF650 Bandit until the weather turned before Christmas.
Since then on cold days the bike starts fine, but then after about five minutes of riding the engine sounds like the choke is on full and the engine runs like a dog at low revs, then cuts out when the revs drop to tickover.
I have checked all the basics and the plugs are sooty but there’s nothing else obvious.
I have had the bike looked at by a mechanic and all appears fine except for a small amount of water in the air box drain tube.
He advised to change the filter as it may be picking up moisture and this is what is causing the carburation problems.
I have ordered a K&N air filter to replace the original as he advised that this would be less susceptible to moisture.
Dave Pyle, email
A. Keep that K&N filter in its box for now as it’s the weather that’s causing you this grief in the form of carb-icing.
All this snowfall has given us day after day of almost 100% humidity with freezing temperatures, the ideal conditions for carb-icing.
If you are doing a daily commute chances are that you spend time at a constant speed with the throttle only fractionally open at 70mph in top gear.
With the carb butterflies cracked open like that the air is going to be rushing through that small gap at 120mph.
This high-speed low pressure air causes the temperature of the air to drop rapidly, lowering the temperature in the venturi through the law of the latent heat of evaporation.
After a few miles that’s enough to lower the temperature of the carb bodies close to Antarctic conditions of -40 ° C while the engine is still showing 80°C!
In those conditions ice will form in the pilot air jet, blocking it and making the bike run massively rich (hence the sooty carbs) until it cuts out.
A few minutes at a standstill and the engine temperature warms up the carbs so that the ice melts and away you go again.
It’s also made worse because the vast majority of vehicles on the roads these days are fuel injected, so icing isn’t an issue for them, which means the fuel on sale in the winter can be refined to be more volatile, so it evaporates more easily, and higher octane super unleaded is even worse, so stay clear of that.
Adding Silkolene Pro-FST and consciously changing the throttle position on a steady run should see it off.