Motorcycle Repair: 1982 honda cb650sc [ 4cyl. single 0hc]

Question
QUESTION: help! pulled carb rack and had a shop clean and install new k&h kit. now fuel leaks intermittently from tubes between 1&2 and 3&4
where rubber 3way joint #16047 460 771 went. my joints are in pieces. are the joints necessary? could their absence be causing the leak? any ideas on what would case fuel to come out of the tubes that I thought were vents. thanks in advance for any insight.
David

ANSWER: David,

These carburetor sets have three sets of interconnecting tubes, which are sealed at both ends with o-rings.  The tube sets connect to supply all four carburetors with (1) Fuel (2) fuel delivery from the accelerator pump and (3) bowl venting.

http://www.cmsnl.com/honda-cb650sc-1982-nighthawk-650-usa_model475/partslist/E++

http://www.cmsnl.com/honda-cb650sc-1982-nighthawk-650-usa_model475/partslist/E++

http://www.cmsnl.com/honda-cb650sc-1982-nighthawk-650-usa_model475/t-joint_16180

The bowl vent system connections could be eliminated or at least not that much of a concern as they only vent gasoline fumes to atmosphere and equalize the atmospheric pressures within the float bowl.

It appears that either the shop did not separate the carburetors for cleaning or they tried to reuse the old o-rings or damaged them in the process of reassembly. It is not a fun job, taking patience and precision to connect all three sets of tubes at the same time, while re-connecting the carburetor throttle and float arm linkages back together again.

Bill Silver


---------- FOLLOW-UP ----------

QUESTION: thanks. the middle link you sent shows the correct part. any idea why fuel would come out of the cast tubes that i thought were vents? [no orings here] thanks for your help.

Answer
The few times I have seen fuel come up out of the vents is when the float valve has stuck open filling the bowls full of fuel which has no where else to go at that point.

When the bowl vents in the roof of the float chamber are plugged, gasoline will shoot out the inlet emulsion tube holes when you turn the gas on. I think your bike has an automatic fuel control valve, which can go bad if the diaphragm has failed.

Bill Silver