Topic: CB750 K7 float valve seat

[Lars]

Hi all,
I have been restoring a CB750K7 which has the PD41A carbs. I am struggling with carb #1, any attempt to adjust the float, it overflows. The float valve needle looks fine, but the brass valve itself seems to have some very fine marks around the bottom hole. I am not 100% positive that the brass valve causes the problem, but I have tried to find that part in order to replace it. Does not seem to be a straightforward job to remove it. Every search on DSS or CMSL ends up with part number 16011-393-004 and that is the needle only. Does Honda not supply this brass valve seat? is it possible to hone any irregularities inside the valve seat, if Honda does not supply them?

Today I will swap the float and needle with one of the other carbs which works fine, just to check out those parts.

Any info would be appreciated.

Lars

[caluser2000]

It could be possible that the float has a small pin hole in it and sinking to the bottom of the bowl. Easy fix with brass floats.

[Lars]

It is not brass floats, so the float is not a problem. I believe it to be the brass float valve seat, into which the needle goes. My questions is; are the brass valve replaceable and if so, where to get the part? If not, is the valve fixable?

[bryanj]

I dont think you can get them out. Look on siriusonic in canada, bit of an unfriendly web site but with what they sell if they dont have it it cant be got.
I have 3 sets of 750 pd carbs in my lockup you could have but the post from UK would be horrendous

[madmtnmotors]

The float valve seat in the PD carbs is not intended to be a serviceable part. This is part of the reason for the switch to rubber tipped float needles in the PD carbs. I have heard of "lapping" the seat with a q-tip and some sort of polishing compound with mixed results.

[Lars]

Bryan, the valves does not look easy to get out, as Wilbur says, they are not a serviceable part. Drilling out might be an option, but if I can't get the part, no point in doing so. I have heard of lapping, too, Wilbur, I might give it a try. Using a Dremel with a soft cone and a polishing compund crossed my mind, but i doubt they have a perfect shaped cone for the job, and maybe too big. I think that project would have gone a little wild. Maybe I should set up an appointment with my dentist, he should have better tools and be more handy on that job than me.

Bryan, I will give it a try, somehow solve that brass valve. Maybe get rubber tip needles. The ones I got are black on the tip, but seems to be harder than rubber. Old and stiff?
If I don't succed, I will be in touch with you, if you are willing to sell.

Lars

[madmtnmotors]

I would try new float needles first. Original Honda float needles hold up best but they are pricey. If you opt for aftermarket make sure they are Viton tip. A Dremel will likely be too aggressive, you only want to polish the brass seat, not cut. I suggest replacing the float needles first. If you still have issues then try polishing the seat.

[Bodi]

swap the needle bit with another carb and see where the leak goes?
I have used the q-tip and brasso or solvol polishing and it actually worked for me, no guarantees of course. I wouldn't go hog wild though - I just spun the swab with my fingers with not much pressure for a while, not spinning it with dremel speed and pushing hard. I tried lapping metal tip CB77 needles in but it's devilishly hard to hold them. Heatshrink tubing got a dubious grip onto a wood skewer but worked, they don't need much spinning with solvol to get a shiny contact ring. Obviously no good for rubbery tips.
A new rubber/viton tipped needle might fix it.

And what did you mean ... it only leaks just after float level adjustments? Is the float tang worn, they often need to be filed flat to avoid the needle button wanting to stay in the little divot worn in the tab from many many hours of them rubbing, so things can get weird after adjustment.

[BenelliSEI]

I polish the seat with a Q-Tip and Autosol.

[Lars]

I swapped needle and float on carb #1 and #4, carb 4 is still good, but carb 1 still leaks. So the needle and the float are not the problem. I have polished the valve seat and will test again after work today.