Petcock Vacuum Line

Cascadia · 08-07-2020, 11:43 AM

Just picked up a 2009 GZ250 under 3000 miles. It was ridden only 500 miles by the last owner, who registered in 2016. So, it was sitting for a while, but the dude I bought it from works at a shop and went through it, cleaned the carb, etc. But, he said it runs best when the petcock is in prime ("PRI"), not "ON." Indeed, it stalls out after a bit when riding in the ON position but has no problems in when riding in the PRI position.

I looked through these forums and found that others have dealt with this issue (http://www.gz250bike.com/forum/showt...ck+vacuum+line) . . .

Checked the the petcock assembly and, lo and behold, it looks like the vacuum line from the back of the petcock to the carb is missing. I've looked through the parts manual but the petcock diagram does not show the vacuum line (https://app.box.com/s/bg53kxt9vwecnr0xm7ab pg. 35). I've also looked through the owner's manual and service manual.

I'm hoping someone would be kind enough to post a picture of their petcock with the vacuum line running from the nipple on the back of the petcock to the carburetor?? I understand from researching that the vacuum line should connect to the carburetor on the top-right-front.

Also sounds like some people just let the bike run in PRI and don't worry about it, but that it could cause problems with the needle.

Any suggestions? Thanks everyone!

Vegas Street Rider · 08-07-2020, 01:09 PM

You definitely need to replace the vacuum line as it regulates the amount of fuel your engine receives when it is running. It could create both lean and rich mixture conditions which could do damage in the long run.

Also, if you leave the petcock in Prime, you could get a situation where the fuel could seep through the carb and into the airbox. Not good.

The vacuum tube does run from the back of the fuel petcock to the carb just behind the throttle wheel on the top right side. If you turn the hand throttle just slightly, you will see a nipple behind that throttle wheel on the carb. Not able to post a pic at this time.

You can pick up some vacuum hose at any auto parts store along with some ring clips. Not sure on size. Probably 1/4" or 3/16" inside diameter. You will only need 6 inches or so. Hope this helps.

Cascadia · 08-09-2020, 01:30 AM

Your description was just as good as a photo! Located the nipple on the carb right behind the throttle wheel and connected a hose from there to the nipple on the back of the petcock (not sure what size the hose is, but it fits snug). Fired right up and has been running great in the "on" position. Problem solved. Thanks so much for your help

Vegas Street Rider · 08-09-2020, 12:14 PM

The other advantage is you now can use the petcock as intended with the reserve switch.

wacio · 08-11-2020, 02:13 AM

Sorry Vegas I need to chime in. The Petcock vacuum valve is only for on/off. The very moment engine is running it just opens fuel and it stays open until engine is shut off. I replaced petcock with manual as many did with no ill effects. You need to cap the nipple at carb to eliminate vacuum leak.
Also this vacuum line is sadly stepped so replacing with generic hose is not straight forward. Its a lot bigger on petcock side.

08-07-2020, 11:43 AM	#1
Cascadia Junior Member Join Date: Aug 2020 Posts: 2	Petcock Vacuum Line Just picked up a 2009 GZ250 under 3000 miles. It was ridden only 500 miles by the last owner, who registered in 2016. So, it was sitting for a while, but the dude I bought it from works at a shop and went through it, cleaned the carb, etc. But, he said it runs best when the petcock is in prime ("PRI"), not "ON." Indeed, it stalls out after a bit when riding in the ON position but has no problems in when riding in the PRI position. I looked through these forums and found that others have dealt with this issue (http://www.gz250bike.com/forum/showt...ck+vacuum+line) . . . Checked the the petcock assembly and, lo and behold, it looks like the vacuum line from the back of the petcock to the carb is missing. I've looked through the parts manual but the petcock diagram does not show the vacuum line (https://app.box.com/s/bg53kxt9vwecnr0xm7ab pg. 35). I've also looked through the owner's manual and service manual. I'm hoping someone would be kind enough to post a picture of their petcock with the vacuum line running from the nipple on the back of the petcock to the carburetor?? I understand from researching that the vacuum line should connect to the carburetor on the top-right-front. Also sounds like some people just let the bike run in PRI and don't worry about it, but that it could cause problems with the needle. Any suggestions? Thanks everyone! Login or Register to Remove Ads
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08-07-2020, 01:09 PM	#2
Vegas Street Rider Senior Member Join Date: May 2015 Location: Henderson, NV Posts: 1,108	You definitely need to replace the vacuum line as it regulates the amount of fuel your engine receives when it is running. It could create both lean and rich mixture conditions which could do damage in the long run. Also, if you leave the petcock in Prime, you could get a situation where the fuel could seep through the carb and into the airbox. Not good. The vacuum tube does run from the back of the fuel petcock to the carb just behind the throttle wheel on the top right side. If you turn the hand throttle just slightly, you will see a nipple behind that throttle wheel on the carb. Not able to post a pic at this time. You can pick up some vacuum hose at any auto parts store along with some ring clips. Not sure on size. Probably 1/4" or 3/16" inside diameter. You will only need 6 inches or so. Hope this helps. Last edited by Vegas Street Rider; 08-07-2020 at 01:12 PM. Reason: additional info
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08-09-2020, 01:30 AM	#3
Cascadia Junior Member Join Date: Aug 2020 Posts: 2	Your description was just as good as a photo! Located the nipple on the carb right behind the throttle wheel and connected a hose from there to the nipple on the back of the petcock (not sure what size the hose is, but it fits snug). Fired right up and has been running great in the "on" position. Problem solved. Thanks so much for your help Login or Register to Remove Ads
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08-11-2020, 02:13 AM	#5
wacio Senior Member Join Date: Apr 2016 Location: Illinois Posts: 174	Sorry Vegas I need to chime in. The Petcock vacuum valve is only for on/off. The very moment engine is running it just opens fuel and it stays open until engine is shut off. I replaced petcock with manual as many did with no ill effects. You need to cap the nipple at carb to eliminate vacuum leak. Also this vacuum line is sadly stepped so replacing with generic hose is not straight forward. Its a lot bigger on petcock side. Login or Register to Remove Ads Last edited by wacio; 08-11-2020 at 02:16 AM.
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08-09-2020, 12:14 PM	#4
Vegas Street Rider Senior Member Join Date: May 2015 Location: Henderson, NV Posts: 1,108	The other advantage is you now can use the petcock as intended with the reserve switch.
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