Topic: Bad shaft seal in Keihin PD carbs - can get a replacement?

[cookindaddy]

Please see the pic below of the bad seal. The rubber is coming away from the seal ring. There are two of these in each center carb, one each on the outside ones. They are the seal for the main shaft that runs through all the carbs. I imagine that they are there to prevent vacuum leaks.

Honda does not show this as a replaceable part. I thought it might be a standard metric shaft seal but it doesn't appear to be. I measure 15mm OD, 10.8mm ID (the diameter of the shaft) and about 4mm thick. I haven't tried to take it out of the casting yet as I will probably destroy it. I have several that are like this.

Has anyone run into this and found a replacement?

My Keihin PD carbs are from a 1978 CB750K, but I think these are used on others?

Thanks!

[boatsdickson]

Too bad this is an older post and I dont have a clear answer, but I have seen this exact problem with my pd carbs on the 78 k8 of my own. I believe these can be replaced with U-rings found on www.crc2onlinecatalog.com or other sites in our FAQ section. I dont have specific sizes for replacements but maybe someone else has an answer for cookindaddy or myself. 

[cookindaddy]

Hey thanks!
I found that out myself. I used U rings from a local O ring shop. It turned out that the inch style fit the shaft and the recess better than did the metric. I have some extras. Do you need some? PM me.

[boatsdickson]

Yup, PM sent. 

[anchorweight550]

you think these might work for the 550 keihin carbs? ill go check mine for the measurements. My bike has been running way lean and the only thing it could possibly be is either from the shaft or the gaskets I made for the caps from gasket material.

[Captaindonutbikes]

damn, if you leave these out will it totally mess up the running of the bike ? there are also some on the lower smaller shaft.

i have just finished a build and i am trying to iron out any faults. the seals on mine were rubbish so not all survived the rebuild. i took these as cushion washers for the shafts and did not think they were involved in the vacuum of the carbs but now maybe thinking this the fault (possibly)

cheers for any feedback

[Tintop]

you think these might work for the 550 keihin carbs? ill go check mine for the measurements. My bike has been running way lean and the only thing it could possibly be is either from the shaft or the gaskets I made for the caps from gasket material.

If the cause of the lean condition is an air leak, it will be 'down stream', between the carb and engine. The PD (46A/C) slides are mechanically actuated (no vaccum), the top seals are dust seals to keep crud out of the bores.  Not having them is like running open velocity stacks on the street.   The choke shaft is slightly differnet in that leakage here would disrupt air flow into the throat.  That said the shaft, butterfly's, and screws are having a much greater effect.   Racers remove them and JB Weld the holes to control air flow, and remove the restriction.

[CBJoe]

Hey thanks!
I found that out myself. I used U rings from a local O ring shop. It turned out that the inch style fit the shaft and the recess better than did the metric. I have some extras. Do you need some? PM me.

Can you post the size of U Ring that worked for you....

thanks, Joe

[anchorweight550]

when i was checking for air leaks, ( replaced carb intake runner boots, o-rings at the head) i found that when i would spray carb cleaner around the carb caps the bike idle would stumble and sometimes crap out. All the throttle slides move smoothly in their bores and nothing telling me they are genuinely worn. Its bizarre to me because I went to take my carbs apart and fix a few things (#2 throttle body had some putty crap the PO put on it and I replaced it) my plugs started looking extremely lean in the midrange.