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Leaking fuel on prime normal?

  • Thread starter Thread starter safwan.khan
  • Start date Start date
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safwan.khan

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Hi friends. I have a suzuki gs450 and it is finally in good running condition except for one thing. I recently rebuilt its fuel petcock and it works great now however, if I accidentally leave it on prime and let the bike stand overnight, I notice that petrol is leaking from the air box where carburetor intake vents fit into. Is this normal? I suspect it could be a clogged "over" line or may be a float needle gone bad? Someone told me that ideally it should NOT leak fuel no matter if it is left on prime. I noticed that when that leak took place, my engine was also filled with gasoline and I had to replace the engine oil before I could take her again for a ride.
Please advise.
 
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Yes, I have done the same thing and gasoline poured all over my garage floor...
Prime position is only for filling the carbs with fuel again after they have been drained or if the fuel in them has evaporated or something.
 
So what you are suggesting is that my carb float needles are intact? If yes, then how come the engine is filled with fuel? My carbs do not leak fuel when running at normal ON mode. Also, what are the indications, if any, that can tell me when my floats or float needle is creating problems and needs replacement / adjustment?
 
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No, carbs in good condition should not leak fuel at all. The fact that very many old carbs are slightly less than perfect and the fact that it is a very minor issue in most cases does not change this.
 
This was a big enough issue that Suzuki issued a service bulletin about this in 1975. Was even a problem for new bikes.

The float + needle valve is intended to control carb fuel level on a running bike.
The problem could occur on a new carb with properly adjusted float levels & might not occur on a 30-year-old carb.

The service bulletin told dealers that they needed to tell owners about this. Owners were to be told that a bike must not be parked with the petcock left in prime.
 
Thanks bro. I didn't know about that bulletin before reading your post below. Seems to me that my floats are not an issue then. But just for knowledge, what could be the indications if ever the floats start misbehaving? My machine is quite old and I cleaned its carbs a couple of weeks ago. Only used petrol for cleaning though. Will do a more comprehensive carb clean this upcoming weekend and then observe how she goes. One of the mixture screws is also quite tight and rotates with significant force through a large screw driver, though I know I cannot crush its tip so I do it tenderly on the inward direction.

jabcb said:
This was a big enough issue that Suzuki issued a service bulletin about this in 1975. Was even a problem for new bikes.

The float + needle valve is intended to control carb fuel level on a running bike.
The problem could occur on a new carb with properly adjusted float levels & might not occur on a 30-year-old carb.

The service bulletin told dealers that they needed to tell owners about this. Owners were to be told that a bike must not be parked with the petcock left in prime.
Click to expand...
 
safwan.khan said:
Thanks bro. I didn't know about that bulletin before reading your post below. Seems to me that my floats are not an issue then. But just for knowledge, what could be the indications if ever the floats start misbehaving? My machine is quite old and I cleaned its carbs a couple of weeks ago. Only used petrol for cleaning though. Will do a more comprehensive carb clean this upcoming weekend and then observe how she goes. One of the mixture screws is also quite tight and rotates with significant force through a large screw driver, though I know I cannot crush its tip so I do it tenderly on the inward direction.
Click to expand...

There is some really good info about servicing carbs on this forum.
Also is a good idea to check the electrical system -- good info here on that too.
 
I'm definitely going to dig deeper in this forum. Looks very promising so far!

jabcb said:
There is some really good info about servicing carbs on this forum.
Also is a good idea to check the electrical system -- good info here on that too.
Click to expand...
 
When I first got my bike running it was dumping fuel out of carb #4. In my case it was a bent float pin that was keeping the float from rising.
 
if fuel is getting past with prime off, it may be the little o ring on the end of the prime screw is faulty. Change it ! , it will be 30 years old.
 
I have completely rebuilt its petcock with hand made parts :) and it works great! I felt it was outrageous to spend 24+ bucks on ordering a K&L fuel petcock rebuild kit so I managed to make it up again using custom sized O-rings that I got from local market which had the exact same fitting. Bought a diaphragm sheet that cost me less than $2 for 2 square feet piece. My overall petcock repair cost was as low as $3 and I have enough diaphragm sheet available with me for making diaphragms for the rest of my bike's life. Now that's cheap! :D

hugo151 said:
if fuel is getting past with prime off, it may be the little o ring on the end of the prime screw is faulty. Change it ! , it will be 30 years old.
Click to expand...
 
If it is still leaking I highly doubt your repair job fixed it. I'd recommend replacing it with a new one from Z1 and not worrying about it for awhile.
 
My floats are OK. Their height was a little bit on the low side which I adjusted in my last carb job. The float pin tips are also looking nice and shiny smooth contrary to my expectations so I've let them stay untouched for now.

BluePlateSpecial said:
When I first got my bike running it was dumping fuel out of carb #4. In my case it was a bent float pin that was keeping the float from rising.
Click to expand...
 
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