venny2522 Posted May 17, 2009 Share Posted May 17, 2009 Hey guys. Trying to get our '67 YR1 up and running, and I have encountered a problem. Fuel flows freely from petcock when it is in the "On" or "Reserve" position. Am I correct in my assumption that it should only flow when the cylinder vacuum pulls it from the petcock bowl? When the petcock is turned on, and connected to the carbs, the fuel rushes mostly to the right hand carb, overflows it, and dumps onto the ground at an alarming rate. TIA for your help, Venny2522 Link to comment Share on other sites More sharing options...
Moderator Airhead Posted May 17, 2009 Moderator Share Posted May 17, 2009 Not correct in your assumption , Vacuum operated fuel taps were developed lmuch later than 1967, the giveaway however is a vacuum line from fuel tap to manifold, if it hasnt got one then its fuel all the time and you have to switch to OFF when not running. Link to comment Share on other sites More sharing options...
venny2522 Posted May 17, 2009 Author Share Posted May 17, 2009 Not correct in your assumption , Vacuum operated fuel taps were developed lmuch later than 1967, the giveaway however is a vacuum line from fuel tap to manifold, if it hasnt got one then its fuel all the time and you have to switch to OFF when not running. Righto. Then it must be a problem with the carbs. What would cause the fuel to start dumping out of the bottom of the carb (vent/overflow?) What regulates/shuts off fuel flow in the carbs that might be at fault? Link to comment Share on other sites More sharing options...
stillooking Posted May 18, 2009 Share Posted May 18, 2009 Righto. Then it must be a problem with the carbs. What would cause the fuel to start dumping out of the bottom of the carb (vent/overflow?) What regulates/shuts off fuel flow in the carbs that might be at fault? I'm not an expert, but I've been having similar problems with a CS5-e 200cc - judging by the forums it's a quite common problem. Have you removed and dis-assembled the carbs yet? If not, clean them internally and particularly inspect needle valve and seat beneath the floats. It might be sticking or worn, allowing the fuel to continually flow through and thus overflow. Also, check float height and verify against proper spec. I'm about to get mine going again to see whether this has fixed it but I just need to try and decoke some of the sludge in the silencers first. Link to comment Share on other sites More sharing options...
peteypops Posted May 18, 2009 Share Posted May 18, 2009 Righto. Then it must be a problem with the carbs. What would cause the fuel to start dumping out of the bottom of the carb (vent/overflow?) What regulates/shuts off fuel flow in the carbs that might be at fault? If you take the float bowl off the carb(s) you'll see the float needle valve on the main body of the carb. It sits between the floats and is normally under a small tang that pushes it up when the bowl is full. If you remove the swivel pin and take off the floats, the needle valve should drop out.Pull out the brass body that the needle was sitting in. Inmost cases on old bikes/carbs it's the o-ring seal on the needle valve body that has hardened off and is allowing fuel to flow through and drain.The needle can also wear but I'd go for the o-ring. However I'm also assuming that the floats are at the correct height? Link to comment Share on other sites More sharing options...
stillooking Posted May 18, 2009 Share Posted May 18, 2009 If you take the float bowl off the carb(s) you'll see the float needle valve on the main body of the carb. It sits between the floats and is normally under a small tang that pushes it up when the bowl is full. If you remove the swivel pin and take off the floats, the needle valve should drop out.Pull out the brass body that the needle was sitting in. Inmost cases on old bikes/carbs it's the o-ring seal on the needle valve body that has hardened off and is allowing fuel to flow through and drain.The needle can also wear but I'd go for the o-ring. However I'm also assuming that the floats are at the correct height? i don't think if they've got an o-ring on the needle valve, mine doesn't on a '72 cs5-e (mikuni) but he'll have to confirm Link to comment Share on other sites More sharing options...
peteypops Posted May 18, 2009 Share Posted May 18, 2009 i don't think if they've got an o-ring on the needle valve, mine doesn't on a '72 cs5-e (mikuni) but he'll have to confirm No probs. The o-ring I'm thinking of doesn't sit round the needle valve but round the brass sleeve that the needle sits in. Thats been a problem on a lot of my keihin & mikuni carbs on singles, twins and fours. Certainly worth tearing the bottom end off the carbs tho' eh? Link to comment Share on other sites More sharing options...
stillooking Posted May 19, 2009 Share Posted May 19, 2009 No probs. The o-ring I'm thinking of doesn't sit round the needle valve but round the brass sleeve that the needle sits in. Thats been a problem on a lot of my keihin & mikuni carbs on singles, twins and fours. Certainly worth tearing the bottom end off the carbs tho' eh? deffo Link to comment Share on other sites More sharing options...
Recommended Posts