Topic: Float needles leaking, which are best replacements, Viton tipped or metal?

[Yamahawk]

My 1971 Cb750 tank is evidently leaking by the petcock, and also through a couple of the float needles. Slow leaks, but leaks nonetheless. I have a drip off the bottom sediment bowl on the petcock, and the valve is leaking by as I am getting gas out the tubes on the bottom of the float bowls. (Overflow vents) A rebuild kit is available for $15 or 39 for OEM, and a replacement petcock is also $29.
Now, what are the best replacements for the float needles? I believe the seats are good, but the metal needles have grooves in them from age and vibration. I cleaned them and polished with 0000 steel wool, and figured I would give them a shot, but they have a slight leak on two of them. Would Viton tipped needles be good to use, and should I replace the seats also? Or just use the same type of needles that are in there now? What float needles and seats are the best? Thanks,
Charlie

[seanbarney41]

In my experience, if your petcock leaks, brand new honda float valves and seats will not stop the carbs from overflowing.  So fix your petcock and always make sure to turn it off when the bike is not running.

[Flyin900]

If you can get viton tips that would be great, yet I think the early bikes only used metal tips and the viton tipped ones were later in the 70's and early 80's

I would replace both the seat and valve as a set. If the valve is worn the seat is too and best to do both. The OEM Honda ones are the best for sure, yet much more expensive to buy. Don't go really cheap as they are sketchy at best and you will be chasing leaks forever. I have used the K&L ones sold by DSS for the CB 400F and they were about $16-18 US per kit X 4 for the carb set.
I am sure they sell a set for the early 750's too.

[TwoTired]

I prefer the metal tipped valves, as they last longer, imo.  But, even with new seats it takes a little bit run vibration to get them to seal  and marry together.  I still have the habit of fuel shut off whenever parked.  The valves can leak if the floats don't swivel properly, even when rubbing the pin post, too. Then there are the dimples on the float tang that can prevent smooth operation of the float swivel.

 For the early fuel taps, they will weep/leak if those two mount screws don't get the proper fiber washers.

Cheers,

[Jerry Rxman Griffin aka MuthaF'er]

Any way to use valve lapping compound on them?

[TwoTired]

Any way to use valve lapping compound on them?

You can.  But, it is easy to overdo.  Ending up with a step in the cone tip.

Cheers,

[Yamahawk]

In my experience, if your petcock leaks, brand new honda float valves and seats will not stop the carbs from overflowing.  So fix your petcock and always make sure to turn it off when the bike is not running.

I always turn it off... but why would it leak through the float needles if it was on? They are designed to Not leak when the float bowls are full. When the petcock leaks by, due to a dried out seal, it keeps the float bowl full, and the float should press the needle into the seat, stopping the leak...

If you can get viton tips that would be great, yet I think the early bikes only used metal tips and the viton tipped ones were later in the 70's and early 80's

I would replace both the seat and valve as a set. If the valve is worn the seat is too and best to do both. The OEM Honda ones are the best for sure, yet much more expensive to buy. Don't go really cheap as they are sketchy at best and you will be chasing leaks forever. I have used the K&L ones sold by DSS for the CB 400F and they were about $16-18 US per kit X 4 for the carb set.
I am sure they sell a set for the early 750's too.

Yep, I can get the K&L float needles and seats... that will be the last resort if new needles won't stop the leaks. I think it is only 1 or 2 of the seats are leaking by.

I prefer the metal tipped valves, as they last longer, imo.  But, even with new seats it takes a little bit run vibration to get them to seal  and marry together.  I still have the habit of fuel shut off whenever parked.  The valves can leak if the floats don't swivel properly, even when rubbing the pin post, too. Then there are the dimples on the float tang that can prevent smooth operation of the float swivel.

 For the early fuel taps, they will weep/leak if those two mount screws don't get the proper fiber washers.

Cheers,

Lloyd, I didn't remove the petcock, so it sat without fuel in it for several months, and those washers were probably dried out. I was hoping that they would swell and seal, but apparently not.  I have used the butt end of a drill bit that fits into the needle seat with a little lapping compound to smooth the seat and allow a needle to seal. These needles were original, I am sure, but are in a later set of carbs, from mid-70's. My friend Pat has some viton tipped needles, I might throw a set in there, as most all modern bikes run them for a reason.
What do you think about the new replacement petcocks? Like this one from 4 into 1..
https://www.ebay.com/itm/Reproduction-Fuel-Valve-Petcock-16950-300-020-Honda-CB500K-CB550K-CB750K/182609898224?hash=item2a8465eaf0:g:iLsAAOSwVlVaI1N1
Would it be a better alternative than rebuilding the stock petcock?

Any way to use valve lapping compound on them?

Being as the needles already have a small ring on them from age and vibration, I should replace them, the seats looked pretty good, but I can lap then with the drill and compound (toothpaste work well) and see if they will seal.
I remember reading from Hondaman's tips about the dimples in the float tangs, also not allowing the needles to seat. How would you eliminate these dimples, without getting new floats?

[Progas]

Always replace the needles and seats together, and use OEM Honda parts. Don't waste your money on after market parts, been there, done that!

[Yamahawk]

Always replace the needles and seats together, and use OEM Honda parts. Don't waste your money on after market parts, been there, done that!

Thanks for the advice! I am going to Honda East this morning and get a new petcock, I see they have them listed on eBay lol... So, once I get the gas to stop flowing into the carbs, I will address the needles and seats. Actually, the seats looked pretty good, and I was surprised that they were leaking by. I will see what they have them for, also.
Charlie

[Flyin900]

I wouldn't try to lap the seats but it's up to you. Again it isn't likely that new valves alone will fix your leaky seats, yet you can try.
It is recommended to always use OEM Honda sets for zero issues and anything else is taking a chance.
Definately test whatever you do with the carbs off the bike with a gas bottle first to avoid finding out they are still leaking after you reinstall them.

[Yamahawk]

Thats the pisser.. I did check each side (two hose feed) with my IV bottle and zero leaks... But, I did start and run the bike the other day, and let it warm up, so perhaps the vibration rotated the needles to a spot where they leaked... or the dimples did their dirty deed.
Charlie

[DaveBarbier]

I remember reading from Hondaman's tips about the dimples in the float tangs, also not allowing the needles to seat. How would you eliminate these dimples, without getting new floats?

Hey Charlie, I haven’t done it, but some people solder a thin piece of sheet steel over the tang. You’ll have to raise your float height (lower the fuel level) to get back to the proper setting but after that it should be good.

[Don R]

 I recently cleaned my seats with mothers polish and Q tips. I was amazed how much black came off of them. I have a newly painted K0 airbox so I'm extra cautious. I rebuilt a different petcock and cleaned the carbs and plan to test everything first.
 I'm still thinking I should buy all new parts rather than risk the paint.

[Yamahawk]

I recently cleaned my seats with mothers polish and Q tips. I was amazed how much black came off of them. I have a newly painted K0 airbox so I'm extra cautious. I rebuilt a different petcock and cleaned the carbs and plan to test everything first.
 I'm still thinking I should buy all new parts rather than risk the paint.

Thanks, Don, the Mother's will polish the brass, and that's where the black came from, good deal! I just got a brand new petcock from the Honda dealer here in Toledo ($43), but it didn't come with new fiber washers and bolts, so I ordered them too, (extra $7 and change) I will install the new petcock, and see what it will do.
I noticed when I was draining my tank on reserve or on, that there was only one of the dual petcock feeds that had gas flowing out of it, and the other one was sucking air into it, even with the filler cap open... I would have thought that both feeds would have been flowing gas, as I was draining it. curious as to why the one flowed and the other didn't. With my carbs, being dual feed, I would have thought it would starve one bank of two carbs if that feed didn't flow gas... 
Charlie

[TwoTired]

Being as the needles already have a small ring on them from age and vibration, I should replace them, the seats looked pretty good, but I can lap then with the drill and compound (toothpaste work well) and see if they will seal.
I remember reading from Hondaman's tips about the dimples in the float tangs, also not allowing the needles to seat. How would you eliminate these dimples, without getting new floats?

If you use a drill with lapping compound, you are likely guaranteed to make a wear step in the cone.   Hand lapping is more than adequate.

For the float tangs, either file flat or fill with silver solder or silver braze if you can control the heat well enough.

Cheers,

[TwoTired]

I noticed when I was draining my tank on reserve or on, that there was only one of the dual petcock feeds that had gas flowing out of it, and the other one was sucking air into it, even with the filler cap open... I would have thought that both feeds would have been flowing gas, as I was draining it. curious as to why the one flowed and the other didn't.

It's all about gravity and a log manifold exit.  It falls out the first down pipe encountered.  Plug the near one and it will happily flow from the second outlet.  On the bike, the float valves do this for you.  Once the carbs fed from the near tube are filled, the far tube supplies the other two carbs.  When all are filled the lines are full and the flow is available to whichever carbs float valve make the demand.

Cheers,

[Yamahawk]

Being as the needles already have a small ring on them from age and vibration, I should replace them, the seats looked pretty good, but I can lap then with the drill and compound (toothpaste work well) and see if they will seal.
I remember reading from Hondaman's tips about the dimples in the float tangs, also not allowing the needles to seat. How would you eliminate these dimples, without getting new floats?

If you use a drill with lapping compound, you are likely guaranteed to make a wear step in the cone.   Hand lapping is more than adequate.

For the float tangs, either file flat or fill with silver solder or silver braze if you can control the heat well enough.

Cheers,

I actually just use a drill bit, and the butt end of that, in a size that fits into the needle seat. I hand lap with the bit and toothpaste lol...
I will have to look at the float tangs when I get into the replacing of the needles later this week.  Got a new petcock today from Honda East, and they had to order the fiber washers, and bolts while they were at it. Thanks, Lloyd!
Charlie

[Yamahawk]

I put the new petcock on using the old screws and fiber washers, as they didn't look bad, and so far so good, no leaks from the petcock... as soon as another nice day appears, its time for a ride!
Charlie

[TwoTired]

I actually just use a drill bit, and the butt end of that, in a size that fits into the needle seat. I hand lap with the bit and toothpaste lol...

Wait, that's not lapping, that's resurfacing.  Lapping marries two parts that are going to live together forever for a perfect contact all around, aided by a dab of abrasive grit.  If you are machining/wearing a surface with a foreign object contour not exactly like what is going to be placed there, the final parts have to resurface each other when they are in service.

It's the same concept of piston ring to cylinder seal and what happens during the break in process.  The parts are lapping each other while in service to make each other smooth and fully seat together.

Cheers,

[Yamahawk]

Technically, yes I agree.The drill bit butt end has a slight, very shallow concave surface (not a cheap poorly ground one from HF lol) which takes out any surface imperfections, and gives the taper on the needle a new sealing edge to mate with. Now, I don't like to use a needle which already has a groove worn into it by contact with the seat, as it will continue to wear and leak at the groove. So, when I do resurface the seat, it gives a new area that will mate with a good needle replacement. I also prefer a Viton tip, as they seem to seal better. I said lap as that is the motion used when lapping a valve into a seat area, even though I wasn't using the needle to lap with.
Charlie

[Bodi]

I don't use lapping compound, even extra fine is pretty coarse for working brass. Just Brasso liquid. A Q-tip in the body first, spun by hand or maybe a battery drill slowly, not for a long time. Then the needle, with it in the drill chuck and a bit (NOT a lot) of polishing. Then a drop on the needle and gently turned in the body with a straw pushed over its back end. This usually works but I have bought replacement valves too. Honda OEM ones are worth the $$$.

[Yamahawk]

yeah, toothpaste works pretty well and is less abrasive the lapping compound or rubbing compound.
Charlie

[setdog]

You can pull the float valve seat, stick into the end of some tubing, insert float valve, add some fuel to the tube, and you should now have way to check if your float valves are seating properly, or you'll have gas all over.

The best float valves are the ones that don't leak.  Viton or metal is of little importance.  I'm of the opinion that oem is always best choice.. But I think viton might have the edge if your seats are a tad off.

Mike Nixon (carb guru)  over at motorcycleproject.com says oem is a must for float valves.

[Don R]

I recently cleaned my seats with mothers polish and Q tips. I was amazed how much black came off of them. I have a newly painted K0 airbox so I'm extra cautious. I rebuilt a different petcock and cleaned the carbs and plan to test everything first.
 I'm still thinking I should buy all new parts rather than risk the paint.

Thanks, Don, the Mother's will polish the brass, and that's where the black came from, good deal! I just got a brand new petcock from the Honda dealer here in Toledo ($43), but it didn't come with new fiber washers and bolts, so I ordered them too, (extra $7 and change) I will install the new petcock, and see what it will do.
I noticed when I was draining my tank on reserve or on, that there was only one of the dual petcock feeds that had gas flowing out of it, and the other one was sucking air into it, even with the filler cap open... I would have thought that both feeds would have been flowing gas, as I was draining it. curious as to why the one flowed and the other didn't. With my carbs, being dual feed, I would have thought it would starve one bank of two carbs if that feed didn't flow gas... 
Charlie

 I noticed the inside of the petcock has one hole that feeds both tubes. I'd think when fuel lines are attached the air can't be sucked back in and both sides will flow.
  I thought I read once someone drilled a second interior hole from the outside and sealed the outside part of the hole like the factory did on the primary one. Just for racing purposes. 

[Yamahawk]

I recently cleaned my seats with mothers polish and Q tips. I was amazed how much black came off of them. I have a newly painted K0 airbox so I'm extra cautious. I rebuilt a different petcock and cleaned the carbs and plan to test everything first.
 I'm still thinking I should buy all new parts rather than risk the paint.

Thanks, Don, the Mother's will polish the brass, and that's where the black came from, good deal! I just got a brand new petcock from the Honda dealer here in Toledo ($43), but it didn't come with new fiber washers and bolts, so I ordered them too, (extra $7 and change) I will install the new petcock, and see what it will do.
I noticed when I was draining my tank on reserve or on, that there was only one of the dual petcock feeds that had gas flowing out of it, and the other one was sucking air into it, even with the filler cap open... I would have thought that both feeds would have been flowing gas, as I was draining it. curious as to why the one flowed and the other didn't. With my carbs, being dual feed, I would have thought it would starve one bank of two carbs if that feed didn't flow gas... 
Charlie

 I noticed the inside of the petcock has one hole that feeds both tubes. I'd think when fuel lines are attached the air can't be sucked back in and both sides will flow.
  I thought I read once someone drilled a second interior hole from the outside and sealed the outside part of the hole like the factory did on the primary one. Just for racing purposes.

When I pulled the old petcock out for replacement with the new one, I noticed that it didn't have a tube that stuck up for on vs reserve... thought that was strange since the replacement OEM one from Honda has a tube at least 2" high... I am thinking PO modification... 
And, the new petcock flows from BOTH openings...
Charlie