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Draining fuel tank on GS750

  • Thread starter Thread starter Firewall
  • Start date Start date
F

Firewall

Guest
Hello,

I'm trying to figure out how to drain the fuel tank on my GS750 (preferably with out removing it). I've done this on my other bikes, but this is the first bike I've had where the petcock does not have an "Off" position.

From reading around, it kinda sounds like with out a vacuum on the line fuel will not flow with the lever in the "On" position. So I should be able to pull the fuel line, then turn the petcock to Prime, right? I'd like to make sure of this before I end up with a big mess on my hand.

Thank you,
Matthew
 
No problem.

Be careful unless you are positive that the petcock is working as is should be.
 
So follow up question, I see replacement of the petcock recommended a lot on here. As far as I know mine is a original 1977 part. However, it worked fine during this procedure (meaning it didn't let fuel flow except for on prime) and there's no fuel in the vacuum line. So I should be OK right?
 
Yea you should. Just keep in mind that if you start seeing fuel leak from the carbs you may be looking a petcock issue since the floats aren't designed to stop fuel.
 
Firewall said:
So follow up question, I see replacement of the petcock recommended a lot on here. As far as I know mine is a original 1977 part. However, it worked fine during this procedure (meaning it didn't let fuel flow except for on prime) and there's no fuel in the vacuum line. So I should be OK right?
Click to expand...

Replacement is recommended if you are having problems with it. Unless you know the complete history of the bike in detail, that part may have already been replaced or repaired prior to your ownership without your being aware of it. Unless you can condemn a part without question, using proper troubleshooting methods, why replace it? You gain nothing and only lose money on the deal.
 
Cowboy..Just an FYI here`. If the needle valve seats and needle valve themselves are in good shape and the float height is properly set, then yes in fact the fuel should be shut off by the needle valves.. thats a basic function in any carb with a float. Thats what its designed to do. It sounds as if the petcock is operating properly. One test i do is to have about a gallon of fuel in the tank. Be sure the petcok is completely wiped dry. Put the petcock in the ON position and set it on a clean piece of cardboard. Let it set for about an hr. and then check for any wetness under the petcock.If its dry then the diaphram is sealing the flow properly..if its wet then you can purchase a rebuild kit from several sources. The thing is that you want to be sure the petcock and needle valves are doing their jobs in concert to prevent slow leakage of raw fuel into the crankcase and contaminating the oil.
 
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hmm. I kind of wish I'd seen this a few weeks ago. I had to drain my tank the hard way by turning it over and spilling it into a funnel. I tried putting it on prime to drain but I didn't get anything.
 
If you put it on prime and nothing came out then there was something wrong with the petcock.
 
chuck hahn said:
Cowboy..Just an FYI here`. If the needle valve seats and needle valve themselves are in good shape and the float height is properly set, then yes in fact the fuel should be shut off by the needle valves.. thats a basic function in any carb with a float. Thats what its designed to do. It sounds as if the petcock is operating properly. One test i do is to have about a gallon of fuel in the tank. Be sure the petcok is completely wiped dry. Put the petcock in the ON position and set it on a clean piece of cardboard. Let it set for about an hr. and then check for any wetness under the petcock.If its dry then the diaphram is sealing the flow properly..if its wet then you can purchase a rebuild kit from several sources. The thing is that you want to be sure the petcock and needle valves are doing their jobs in concert to prevent slow leakage of raw fuel into the crankcase and contaminating the oil.
Click to expand...

Thanks Chuck.
 
How does that make sense..the purpose of the prime feature is if the bike is totally out of gas or the carbs are being put back on and the bowls are dry..you need a way to PRIME them without vaccuum..If theres no fuel in the tank or carbs then you in cant start the bike like say on the side of a road and your out and someone stops and gives you some gas..At that point just how do you suspect you can apply a vaccum to get it started??? It should flow freely on prime without any assist from anything..thats how it works. Prime= free flow of fuel WITHOUT any vaccuum required..ON = fuel flow ONLY while engine running to supply vaccuum..Resereve = sama as on.
 
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chuck hahn said:
How does that make sense..the purpose of the prime feature is if the bike is totally out of gas or the carbs are being put back on and the bowls are dry..you need a way to PRIME them without vaccuum..If theres no fuel in the tank or carbs then you in cant start the bike like say on the side of a road and your out and someone stops and gives you some gas..At that point just how do you suspect you can apply a vaccum to get it started??? It should flow freely on prime without any assist from anything..thats how it works. Prime= free flow of fuel WITHOUT any vaccuum required..ON = fuel flow ONLY while engine running to supply vaccuum..Resereve = sama as on.
Click to expand...

I suspect it was a design flaw? Anyways its just what I heard.

Also in normal circumstances the starter will produce enough of this allegedly required vacuum.
 
It will take about 30 to 40 seconds for the bowls to fill and then you gotta actually have enough battery power left to start the bike..thats why the petcock is designed that way.. Suzuki and several sources sell the rebuild kits. Not terribly expensive either.
 
Aj..Knowyourenemy has a few in the parts for sale section......he is a good guy and i have had many a deal with him..good source.
 
Listen bub, I'm just repeating what I heard in another thread some months ago.
Its not that it needs constant vacuum, just a blip to get it started.
 
well I was having trouble getting my bike started what I did was take the hose off of the petcock and took a tiny syringe pump and started pumping into the hose. this helped me get the bike started. however not something I'd like to do every time I go to ride.
 
Im really grateful that my petcock works good.

Because I tend to read nothing but problems from most riders on here!:D
 
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