air sucking sound vt500 - Honda Shadow Forums : Shadow Motorcycle Forum

CrashOverride · 08-13-2010, 07:46 AM

VT500c gravity fed petcock. Had an air sucking sound coming from the hose that goes from the petcock to the engine on the lefthand side. Small crack in the hose little tape and issue went away.

Started again this morning, got that sucking sound and bike would not idle. More tape lol and moved it around a bit and ran fine at idle and speeds.

I will replace the hose tonight, what type of material should I get? Is a special kind needed to withstand the engine heat?

Also what does that air hose do? Does the engine start and then use it as a vacuume to help pull the fuel from the tank down into the carbs?

Thanks

Crash

snickers_163 · 08-13-2010, 10:18 AM

The hose uses engine vacuum to operate the diaphragm in the automatic petcock. Vacuum opens the valve and lets fuel flow to the carbs. Replace the line and you will be fine. I used some 3mm ID high temp silicone because that's what I had laying around, but you shouldn't need anything fancy. Rubber vac hose or fuel hose will do as long as the inner diameter (ID) is small enough. 3mm or 1/8" should do.

ExTex · 08-13-2010, 10:24 AM

The hose is a vacuum line from the engine intake to the petcock.
The petcock is an "automatic" valve that is vacuum operated to let fuel go from the gas tank to the carbs.

Take the old hose to an auto parts store. They can match the diameter and sell you the length you need.

With a leak in the hose, the petcock won't open to feed the carbs.
Also the engine may run poorly due to the extra air being sucked into the cylinder.

While you are working on the petcock area, you may want to test the petcock. With no vacuum, there should have no gas flow in any of the 3 positions.
With vacuum (you can suck on the hose enough to open the petcock), there should be gas flow in the ON and RES positions, but no gas flow in the OFF position.

Ride safely,

CrashOverride · 08-13-2010, 10:32 AM

Thanks for the info.

I was going to stop by the store on the bike so I don't have the tube off yet and its kinda stuck on good so i may have to cut it off.

The schematics for the hose say 3.5X75. Is that 75mm long with a 3.5 internal diameter?

Thanks

Crash

still_bluenoser · 08-13-2010, 02:25 PM

Any hose that will jam over it and seal will work. Very low suction.

08-13-2010, 07:46 AM	#1 (permalink)
CrashOverride Senior Member Join Date: Jan 2010 Location: St. Catharines, Canada Posts: 589	air sucking sound vt500 VT500c gravity fed petcock. Had an air sucking sound coming from the hose that goes from the petcock to the engine on the lefthand side. Small crack in the hose little tape and issue went away. Started again this morning, got that sucking sound and bike would not idle. More tape lol and moved it around a bit and ran fine at idle and speeds. I will replace the hose tonight, what type of material should I get? Is a special kind needed to withstand the engine heat? Also what does that air hose do? Does the engine start and then use it as a vacuume to help pull the fuel from the tank down into the carbs? Thanks Crash __________________ 1984 VT500C Shadow Ox Blood Red

08-13-2010, 10:24 AM	#3 (permalink)
ExTex Senior Member Join Date: Jul 2007 Location: Southeast Arkansas Posts: 462	The hose is a vacuum line from the engine intake to the petcock. The petcock is an "automatic" valve that is vacuum operated to let fuel go from the gas tank to the carbs. Take the old hose to an auto parts store. They can match the diameter and sell you the length you need. With a leak in the hose, the petcock won't open to feed the carbs. Also the engine may run poorly due to the extra air being sucked into the cylinder. While you are working on the petcock area, you may want to test the petcock. With no vacuum, there should have no gas flow in any of the 3 positions. With vacuum (you can suck on the hose enough to open the petcock), there should be gas flow in the ON and RES positions, but no gas flow in the OFF position. Ride safely, __________________ 1983 Nighthawk 650 1989 VTR250 1985 Sabre 700 - - Sold 1983 Shadow 500 - - Sold 2006 Ninja 500- - - - Sold

08-13-2010, 10:32 AM	#4 (permalink)
CrashOverride Senior Member Join Date: Jan 2010 Location: St. Catharines, Canada Posts: 589	Thanks for the info. I was going to stop by the store on the bike so I don't have the tube off yet and its kinda stuck on good so i may have to cut it off. The schematics for the hose say 3.5X75. Is that 75mm long with a 3.5 internal diameter? Thanks Crash __________________ 1984 VT500C Shadow Ox Blood Red

08-13-2010, 02:25 PM	#5 (permalink)
still_bluenoser Senior Member Join Date: Mar 2008 Location: Nova Scotia Canada Posts: 3,476	Any hose that will jam over it and seal will work. Very low suction. __________________ 1981 cb750c with 900f forks, cams, oil cooler. 1983 vt500c 1979 cbx

08-13-2010, 10:18 AM	#2 (permalink)
snickers_163 Member Join Date: Jul 2010 Posts: 69	The hose uses engine vacuum to operate the diaphragm in the automatic petcock. Vacuum opens the valve and lets fuel flow to the carbs. Replace the line and you will be fine. I used some 3mm ID high temp silicone because that's what I had laying around, but you shouldn't need anything fancy. Rubber vac hose or fuel hose will do as long as the inner diameter (ID) is small enough. 3mm or 1/8" should do.

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