Carb question

[93NJST]

When I ride my ST1100 in cold weather (below 32 deg) it sometimes starts to bog down. Almost as if the air flow was getting cut off. I heard mention of "carb freez". Can anyone better explain what it is and how to help prevent it.

Cheers,
Adam

 

[electrajoe]

Put a rag in the right carb inlet duct, forward in mid-faring. My 1991 has left and right, the left was later eliminated due to carb icing. Never had this problem, however, I don't ride much under 40F.

 

[93NJST]

Thanks for the info,
I am wondering, wouldn't the rag cut the air supply to the carb? Also, what year did they eliminate the left intake. I never noticed if my 93 had two.

What causes the iceing? Is it a fuel problem in the carb?

Cheers,
Adam

 

[electrajoe]

The air duct ends about 9 inches in front and above the air filter inlet port, there is plenty of air under there even without the duct. Just a case of Honda 's over-engineering on the ST1100.

Motor Cycle News (MCN) says "eliminated air snorkle" on later 1991 models.

"Carb icing occurs when there is humid air, and the temperature drop in the venturi causes the water vapour to freeze. The ice will form on the surfaces of the carburetor throat, further restricting it. This may increase the venturi effect initially, but eventually restricts airflow, perhaps even causing a complete blockage of the carburetor. Icing may also cause jamming of the mechanical parts of the carburetor, such as the throttle butterfly valve." from:

http://en.wikipedia.org/wiki/Carburetor_icing

Also try a bottle on gasoline dryer (Heet). The alchol, mixed with both water and gasoline and is burnt. However you probably are getting ethanol in your gasoline anyway.

 

[Reg_Siemens]

Adam - Have you tried bypassing the vacuum shutoff valve? There's been some discussion that what has previously been attributed to carb icing might in fact be a marginal vacuum shutoff diaphragm where symptoms only become noticeable at low temperatures. Since it's so simple to bypass, it would be worth a try for some of your cooler rides to see if it solves your problem.

 

[93NJST]

Thanks Joe for all that info. I'll have to try it out tomorrow morning.

Reg,
Do you have any instructions on how to bypass the vacuum shutoff?

Cheers,
Adam