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Fuel petcock question

J

jetta90

Forum Mentor
I have a 1984 GS 750E I'm slowly getting it back to some sort of roadworthy condition.
Last night I took it out for a first road test around the block a couple of times....................its not licensed yet.
When I run it with the petcock on " on " its fine. When I turn the fuel petcock to " res " after 5 or ten seconds I get fuel running out the petcock vent tube. I don't even have to run the bike on RES for it to leak. I can turn the bike off and turn the lever to RES, wait 10 seconds or so and it'll leak.
I wouldn't have thought that could be possible, ok on the on position and fuel leaking on the reserve position.
Anyone out there had a similar problem? Anyone have a recommendation to repair? Or is it simply a bad petcock?
tx
 
Petcock vent tube?
You mean the vacuum port that is supposed to shut off fuel flow if there is no vacuum signal?
If you have fuel leaking out of that, then yes, your petcock is bad.
They can be rebuilt, but most of the guys here will just advise you to buy a new one as most rebuild kits are junk.
 
Are you sure you are setting it on RES and not on PRI? :shock:

I had a discussion with a couple of riders some time ago to try to convince them of the proper operation of their petcock. They thought there was a 'pointer' opposite the 'flag' that you grip to turn the petcock, and the 'pointer' showed the setting. I had a hard time convincing them that, if their logic was correct, why was the 'pointer' pointing away from the word ON when the bike was running? It is the 'flag' that points to the setting.

(Bike Bandit does not show an '84 750, so I am basing this on the picture for the '83.) For normal operation, the 'flag' should point down to the ON position. For RES, rotate the petcock clockwise, pointing the 'flag' forward. Conversely, rotate it counter-clockwise (pointing the 'flag' rearward) for PRI.

If you are mistakenly setting it in PRI, thinking it's RES, that might overpower the float valves, making the carbs leak out the vent tubes. If that is the case, you need new float valves.

.
 
Thank you for responding.

I think I got the working logic figured out on the fuel tap.

It does leak big time on RES and PRI, regardless of weather the bike is running or not.
What I don't understand at this point, and i didn't do a good job explaining in my initial post, is why would the bike run fine with no leakage on the ON position but leak on the RES and PRI?
Does it not make sense that if the ON position operates correctly then the RES should also be working as well?
Both the ON and RES system fuel flows within the same passages, don't they?
 
My apologies. My bad.

Upon closer verification i can see where i'm way out to lunch on this one.
The leak is coming from the overflow tube between carb 3 and 4 and not as I had explained it before. I checked to see if i had routed the vent line properly and no I had not.
The proper routing for both vent lines should be up above the air filter box then back down.
So, the lines are now rerouted to above the air box and then down along the side of the air box..................now my lines are to short to go further down to behind the crankcase. I'll fix that with longer vent lines.

I don't know if that is why fuel was leaking from the vent tube on RES and PRI as I've read somewhere on this forum that some people don't run vent lines at all.
 
jetta90 said:
My apologies. My bad.

Upon closer verification i can see where i'm way out to lunch on this one.
The leak is coming from the overflow tube between carb 3 and 4 and not as I had explained it before. I checked to see if i had routed the vent line properly and no I had not.
The proper routing for both vent lines should be up above the air filter box then back down.
So, the lines are now rerouted to above the air box and then down along the side of the air box..................now my lines are to short to go further down to behind the crankcase. I'll fix that with longer vent lines.

I don't know if that is why fuel was leaking from the vent tube on RES and PRI as I've read somewhere on this forum that some people don't run vent lines at all.
Click to expand...

You shouldn't leak fuel from the vent tube when the bike is off and the petcock is either in the "on" or "res" position, to do so means your petcock isn't working properly. Also to leak fuel from the carb vent tubes for any reason means your float needles aren't closing like they should when the float bowl gets full.
 
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