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1979 GS750L - Fuel leaking from carb 1 when running or on PRI

  • Thread starter Thread starter breckenedge
  • Start date Start date
B

breckenedge

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Floats set too high? Stuck? Fuel flows out the circled hole when the engine is running or petcock set to PRI.

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Thats a very likely candidate along with the float valves condition. Check the heights and then look at the float valve..some have the rubber tips and some are just solid. If they are rubber tipped look for any deterioration of the tips or signs of grooves or other marks on them. Look at the valve seats as well for damage, gunk on the sealing surfaces etc etc. Also if the float pin has a little plunger in the top be sure its loose and springy as well. And if you have the old brass solderd together floats , shake them around and be sure they havent leaked and took on fuel..that will weigh them down and cause all kinds of problems.. best to replace if they are ful of fuel..you will most likely have the composite floats though in that year bike.
 
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Yes, float needle not sealing. Most likely crud from the tank is fouling the works.
 
On prime the float needles should at least stop the flow of gas, and by that I mean it shouldnt let it noticable run out the overflows. And if its running it certainly shouldnt run out the overflows. If the floats are set and working properly ,the engines usage of fuel should be in harmony with the float metering the amount of fuel being fed to them from the tank..syncronisity of sorts.
 
Turning the screw nearest that hole sets the height? I am clueless regarding motorcycles. Unfortunately that screw is very stripped and difficult to turn. Any suggestions?
 
Good point on tank crud ED.. He may also want to pull the petcock and look at the pick up screen attatched to the petcock. I actually had one come out of the recess and couldnt figure out why it was always getting crap down stream. Also take a pen light and look in all the holes at as much of the tank interior you can. Determine if its in need of a cleaning or even coating . just a few thoughts here as to preventative maintenance up stream of the carbs.
 
chuck hahn said:
determine exactly where the gas is seeping from first...then post that up.
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Thanks for the replys. It comes straight out the circled pipe when either running or set to prime, otherwise fine. I'm guessing that's called the 'drain hole'?
 
Its the bowl overflow ..the screw next to it is the bowl drain plug which has nothing to do with float height..its just a drain..if it aint leaking leave it be. I deleted the post about gas flowing to the lowest point. I rechecked the pic and there isnt any way gas leaking from the drain plug could run sideways to the nipple. So yes i think its a stuck, dirty. or damaged float needle and youll have to inspect inside anyways so you may as well check the float height while the bowl is off the crab.
 
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When BASSCLIFF sends you his mega welcome package, and he will be along shortly, Read every tutorial and ALL the info in there. Your gonna eventually run into almost every issue addressed in that mega welcome. It will serve you well to save it in your documents for fast and easy reference in the future.
 
chuck hahn said:
When BASSCLIFF sends you his mega welcome package, and he will be along shortly, Read every tutorial and ALL the info in there. Your gonna eventually run into almost every issue addressed in that mega welcome. It will serve you well to save it in your documents for fast and easy reference in the future.
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Yea I've been reading many of his tutorials and posts, very helpful. Thank god the Dallas public library has both editions of the Clymer manual.

FYI the photo looks sideways on my iPhone, but upright on my PC. Apple :-/
 
You also know the petcock is working correctly because in the ON position with the engine not running it is supposed to shut off all fuel flow and it appears to be doing just that. You said it only happens while the bike is running which means there is vaccuum at the petcock and gas is flowing . When the bike is off..no vaccuum and the petcock close. This is exactly what you want to happen. On prime, the petcock is designed to bypass the requirement for a vacuum. In case you completely run out of gas, you need to drain the tank for maintenance..whatever may cause the a tank to become fully dry, You obviously need to reprime the carbs to try and restart the bike. Thats the purpose of the prime setting. Once the carbs are primed and the bike starts you then rotate down to the RUN position and leave it there unless you need the reserve. Does all that make sense as to the petcocks positions and functions?
 
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chuck hahn said:
You also know the petcock is working correctly because in the ON position with the engine not running it is supposed to shut off all fuel flow and it appears to be doing just that. You said it only happens while the bike is running which means there is vaccuum at the petcock and gas is flowing . When the bike is off..no vaccuum and the petcock close. This is exactly what you want to happen. On prime, the petcock is designed to bypass the requirement for a vacuum. In case you completely run out of gas, you need to drain the tank for maintenance..whatever may cause the a tank to become fully dry, You obviously need to reprime the carbs to try and restart the bike. Thats the purpose of the prime setting. Once the carbs are primed and the bike starts you then rotate down to the RUN position and leave it there unless you beed the reserve. Does all that make sense as to the petcocks positions and functions?
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Yep makes perfect sense. I didn't know diddly about this feature and ended up with a drained tank the first night, haha. In regards to the manual, I noticed none seem to reference an inline fuel filter.
 
Not a good idea..just another area of resistance for the fuel to have to flow thru. Theres a periscope lookin filter insatlled in the petcock inside the tank..Its also a good idea to be sure of the tanks interior condition as far as rust or slime built up inside from stale gas setting in it. Just me here, but experience has taught me to not take anyhting for granted. Its good to take the petcock off and be sure 1..that the strainer is there, 2.. that its clean and 3..the tank is spotless inside and if its rusty it may be a good idea to derust or even consider doing the POR 15 tank coating. Junk getting dislodged and finding its way down to the carbs is like having the arteries to the heart sudenly blocked. It kills a bike instantly . Run fine one day and then the next your hit.
 
breckenedge said:
Yep makes perfect sense. I didn't know diddly about this feature and ended up with a drained tank the first night, haha. In regards to the manual, I noticed none seem to reference an inline fuel filter.
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You're right there is no in-line fuel filter. There is a filter sock on the petcock and filter screens on each carb inlet on top of the float needle valve.
 
Well got the bowl off and fuel stops flowing if I manually push the float up, simulating a full bowl. So, stuck float? It's the old plastic kind, doesn't appear to be cracked though.
 
Shake the float next to your ear..ifm its been compromised youll hear fuel in it swishing..vigorously..any noise and it has fuel in it,,doesnt have to look cracked to be bad.
 
chuck hahn said:
Shake the float next to your ear..ifm its been compromised youll hear fuel in it swishing..vigorously..any noise and it has fuel in it,,doesnt have to look cracked to be bad.
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I moved the bowl a bit while it was dangling from the carb, doesnt appear to have any fluid in it. Put it all back together, and now it appears to be working well.

I think that some crap was clogging and stopping the pin that the float touches and prevented the float from rising and stopping the fuel. I'll have to do a full teardown next weekend. The carbs were just cleaned last weekend, so the new buildup is likely due to junk in the fuel tank.
 
Well we already posted about the screen and the possibilities of the tank being in need of some attention..Glad that at least for now you can ride it again.
 
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