fivestring
CB750 Member
I have a '78 SOHC with the PD42 carbs. I purchased four rebuild kits that included the bowl rubber gasket, needle and some o rings. I also purchased a new accelerator pump which came with a new spring and a rubber dust boot. None of the kits I got included the tiny o ring that goes between the bowl and carb body to seal the passage where the accelerator pump squirts gas up into the carb body. And my carbs were missing this little seal when I opened them up (bike was not running when I bought it). Here's a good picture of this elusive little critter, although it is from a Honda CBX carb:
I tried to find a replacement o ring from my collection. None seemed to work, either they were too thick and closed off the passage so no gas came out the tubes in each carb venturi or my attempt at using silicone sealer would fail and allow the gas to leak right back into the bowl or leak outside the carb bowl. No matter what I used, I was not getting the little stream of fuel that is so necessary to acceleration from idle.
After removing, installing, removing, and bench testing several times, I was at wit's end. I thought, "why didn't they just use a paper type gasket to seal everything like my Mikunis do?" So I looked around and found an old paper-type gasket from the top cover of these Kei Hin carbs. I cut a small circular gasket from the largest screw hole in that gasket, put a tiny bit of sealer on it and put it together, sandwiching this new gasket in place of the missing little o ring seal between bowl and body. I used the regular rubber bowl gasket, I didn't change anything there.
So far, with bench testing, it seems to be doing the trick. I tightened the bowl screws a little extra snug to be sure the bowl would not leak. I'm finally getting four tiny streams of gas with each throttle movement.
I'll update once the carbs are mounted and working properly, or not.
I tried to find a replacement o ring from my collection. None seemed to work, either they were too thick and closed off the passage so no gas came out the tubes in each carb venturi or my attempt at using silicone sealer would fail and allow the gas to leak right back into the bowl or leak outside the carb bowl. No matter what I used, I was not getting the little stream of fuel that is so necessary to acceleration from idle.
After removing, installing, removing, and bench testing several times, I was at wit's end. I thought, "why didn't they just use a paper type gasket to seal everything like my Mikunis do?" So I looked around and found an old paper-type gasket from the top cover of these Kei Hin carbs. I cut a small circular gasket from the largest screw hole in that gasket, put a tiny bit of sealer on it and put it together, sandwiching this new gasket in place of the missing little o ring seal between bowl and body. I used the regular rubber bowl gasket, I didn't change anything there.
So far, with bench testing, it seems to be doing the trick. I tightened the bowl screws a little extra snug to be sure the bowl would not leak. I'm finally getting four tiny streams of gas with each throttle movement.
I'll update once the carbs are mounted and working properly, or not.