Fuel leaking from CAV Valve air vent

Myvatexman

Joined
May 3, 2015
Messages
4
Location
Geneva, IL
I had been riding along nicely on my 93 ST1100 with 49K miles -then after a few aggressive miles I smelled fuel and the bike stalled out- it got it running roughly and stumbled home but went through l1/2 tank of gas in 10 miles . After taking off the plastics and restarting it, I could see gas pouring out of the CAV Valve front air vent port. It stops when turn engine off. Does anyone have any ideas on why and where the gas is coming from? I am wondering if this CAV valve can be bypassed somehow ? I have read a number of threads about pressure in the gas tank which is also something that I have noticed upon opening the cap but am at a loss because I can find nobody that has had this issue before.
 
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Without knowing what a CAV valve is, I would guess its a stuck float in the carb. SWAG - not knowledge here.
 
Slydynbye said:
CAV valve?
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Never have seen that term used either, in the decades that I have owned ST1100's.

Possibly the OP is referring to the fuel cutoff valve?? If so, simple fix is to remove it and throw it away and reconnect the fuel line. Also, plug the vacuum line that went to the valve.
 
93 ST1100 standard California type and USA ABS/TCS type with a Purge Control Valve (PCV) and Air Vent Control Valve (AVCV) at the front of the carbs?
 
Yes let me clairfy the name of the part. The manual refers to the Evap Carburetor Air Vent Control valve as the CAV valve or EVAP CAV sorry for the many names but I think it must be an emissions system to vent fumes back to the Evap canister from the float bowls when engine is off and allows them to breath from atmosphere when running. But mine spews out fuel from the air vent port. Any ideas?
 
Ok, if this valve or port is spewing gas from the float bowls, that means you have a stuck float or dirt under the needle, allowing gasoline to flow into the carb float bowl. I had gas pouring out of a vent on a carb years ago when the float got stuck. I think you have a vacuum powered fuel valve, so when you shut the engine off, the gas line to the carbs is shut off, and the leak stops. My money is on one of the carb floats.
 
OK thanks I am pulling the carbs off tomorrow to give a good cleaning . Thank for the suggestions I'll let you know how it goes.
 
X2 on float needles. Pull the carb, clean it up, check float height and needles, etc. Also make sure your fuel pipe O-rings are not the culprit.
 
X3 on float/needle. What manual are you quoting that created the "CAV" acronym? Not in my Honda or Haynes...

The 49 state standard, non-ABS models don't have this valve.

John
 
before you just pull the carbs follow the hoses from the "CAV" and see which one is getting fuel in it. There has been more that a few times lots of work was done that did not fix the problem from guess repairs. Pull the hoses off and locate the fuel source.
 
Well you guys know your stuff - you were 100% right on the money ! Thanks SMSW for first pointing me in the right direction and getting me started and the rest of the posters for agreeing and telling me the solution. I spent Sunday pulling the carbs and then giving them a thorough cleaning. Could not tell which carb was the culprit- but it solved the problem now running smooth and no gas leaks from the air vent port of the AVCV. I also must have got some fuel in the engine so as soon as I saw no leak- I did a fresh oil change and apart from a few hiccups on first firing it up -to burn off the leaked fuel I guess it smoothed out within 20 seconds. I must say that the leak might have been quite dangerous as the fuel coming out of the port pours straight down the right side of the engine and onto the hot exhaust. So I am going to run a hose from the AVCV port to drain safely below the bike incase this ever happens again. FYI my naming conventions on the part come from page 274-275 of the Clymer ST1100 Service manual where they refer to this item by several names but full name appears to be Evap Carburetor Air Vent Control Valve . Now to put all the plastics back on and get ready for next weekends ride! Thanks again for the conviction of the problem and as well as the likely solution.
 
Myvatexman said:
Well you guys know your stuff - you were 100% right on the money ! Thanks SMSW for first pointing me in the right direction and getting me started and the rest of the posters for agreeing and telling me the solution. I spent Sunday pulling the carbs and then giving them a thorough cleaning. Could not tell which carb was the culprit- but it solved the problem now running smooth and no gas leaks from the air vent port of the AVCV. I also must have got some fuel in the engine so as soon as I saw no leak- I did a fresh oil change and apart from a few hiccups on first firing it up -to burn off the leaked fuel I guess it smoothed out within 20 seconds. I must say that the leak might have been quite dangerous as the fuel coming out of the port pours straight down the right side of the engine and onto the hot exhaust. So I am going to run a hose from the AVCV port to drain safely below the bike incase this ever happens again. FYI my naming conventions on the part come from page 274-275 of the Clymer ST1100 Service manual where they refer to this item by several names but full name appears to be Evap Carburetor Air Vent Control Valve . Now to put all the plastics back on and get ready for next weekends ride! Thanks again for the conviction of the problem and as well as the likely solution.
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I would recommend putting on a new fuel filter to make sure nothing get into the needle and seats.
 
Myvatexman said:
Well you guys know your stuff - you were 100% right on the money ! Thanks SMSW for first pointing me in the right direction and getting me started and the rest of the posters for agreeing and telling me the solution.
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Speaking for myself, and I am sure everyone else, glad to be able to help. These problems are usually not a case of you "going where no man has gone before...."
 
If you have an intact rubber barrier pad between the carb body and the top of the motor, the added drain line will not be necessary. I agree though, fuel flowing over hot exhaust is not comforting. X2 on the fuel filter.
 
Not sure if this is the place to reply since I am new here but this is what happened with my 99 yesterday-It had been sitting for four days and when I started it after a few minutes of idling I noticed gas leaking from the front of the engine-it was seriously dripping into a puddle but running smooth-I cut it off and let it sit for a couple hours and started it again-no leak. Today I started it and ran it twice-no leaking. Any advice or suggestions would be greatly appreciated-thanks and I am enjoying this forum.
 
rmcc12 said:
Not sure if this is the place to reply since I am new here but this is what happened with my 99 yesterday-It had been sitting for four days and when I started it after a few minutes of idling I noticed gas leaking from the front of the engine-it was seriously dripping into a puddle but running smooth-I cut it off and let it sit for a couple hours and started it again-no leak. Today I started it and ran it twice-no leaking. Any advice or suggestions would be greatly appreciated-thanks and I am enjoying this forum.
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Check your coolant system.
 
I know this is an old post, but I've just won a battle against the EVAP (Evaporative Emission) CAV (Carburetor Air Vent) valve and its partner, the EVAP Purge Valve. In the 91-02 ST1100/A Honda Service Manual, these two vales are shown on page 1-44. Only important to all CA bikes and early US ABS/TCS. STerling is (was) a CA bike.

EVAP CAV valve resides right behind the thermostat housing with a bunch of hoses connected. EVAP Purge resides at the front-left of the carb set, again with a bunch of hoses. Their combined purpose are to collect and purge vapors from the carbon canister on top of the swingarm and to provide atmospheric pressure to the carb diaphragm. I'm adding a detailed description to my thread Surprise! Surprise! concerning STerling.
 
Another thread where a little reading & looking is going to save me a lot of time. I’m at that stage where a ten minute job is taking me 2 hours so I am appreciative.
 
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