Viton Float Valves for older carbs

[81xsproject]

I discovered a way for folks with older brass needle vavle assemblies to get and use Viton tipped ones. Here are some pics of the two different types installed. The only difference that I can see so far, is that the filter screen is attatched, they use a metal washer instead of a fiber, and as best as I could measure, the Viton needle sticks up ~.035" higher than the brass assemble. However, this comparison is between an old worn out brass assembly with already crushed fiber washer and a brand new Vitron assembly with uncrushed washer. I imagine this is SOME of the difference. Still very close. Both seats have size 2.0 openings so there shouldn't be any fuel supply issues.





I found these at Z1enterprises and thought I would get some to see if they would work on a pair of '78 carbs I am rebuilding to sell.

They apparently fit:

Float Needle Valve Assembly - Fits Yamaha XJ650G/H/J/K/LH//RJ XJ700N/NC/S/SC XV700L/LC/N/NC/CS/CSC/CT/CTC/SS/SSC XJ750J/K/MK/RH/RJ/RK XV750H/J/K/MK XV920J/K/MK/RH/RJ XV1000L/LC/N/NC XV1100S/SC/T/TC

I will report more as I get everything back together and take the carbs for a spin.

[somesuch]

Oh, one week to late for me this time, I just put in a set of new Mikuni valves that I got from K+L supply. Good info! Thanks
--Nick

[Ken Talbot]

The way I figure it, .035 is pretty close to 0.9mm That much difference, at 6.0mm from the centreline of the float pivot to the end of the needle, will proportion out to approx 7mm difference out where you measure float height, which is approx 45mm away from the centreline of the float pivot. I'm not saying it won't work, but I'm saying you will need to do some fairly major resetting of the float level. I would be concerned about having to bend the tab so much that it wold no longer be anywhere close to perpendicular to the spring loaded pin. It might make more sense to carefully grind or file that 0.035 off ot the end of the pin.

JAT, YMMV

[81xsproject]

I will keep an old set up and with the same float set it up both ways to get an actual difference at the float. Maybe tonight, but no promises

[81xsproject]

Good news, measuring small distances by eye is extremely inaccurate . Using a much more scientific process that an caliper assisted eyeshot, they difference is much smaller. I installed an old brass assembly, torqued the seat down, installed the float, them measured float height; 1.048". Then I removed the old one, and in the same carb, installed a Vitron setup, and checked the float height; 1.033". So the difference between the two setups is (at the float) .015" or 3.81mm. So, no EXTREME float adjustment required.

[Ken Talbot]

That sounds promising, but let me get this straight. The Viton tipped needle is a bit longer than the stock one, but once installed, it makes the float sit lower? What am I missing?

[81xsproject]

Sorry, Ken caught my boo boo. The measurments are backwards. The Vitron is longer and corresponds to the higher float height.

[skids]

'Course you could just get a thinner fiber washer from the hardware store.

Originally posted by 81xsproject
Sorry, Ken caught my boo boo. The measurments are backwards. The Vitron is longer and corresponds to the higher float height.

[81xsproject]

or even better, remove the washer all together and seal the thread with fuel resistant thread tape which is what I like to do anyway.

[81xsproject]

Since it came up, I thought I would revive this to give the final report on the upgrade. It works very well. I adjusted the floats 1-2mm to get them to spec. Once the carbs were on, I opened both the petcocks and let them sit for about and hour. No dripping. When I took them out for a test ride, I did everything I could to try and starve the carbs by running WOT. I couldn't get them to starve, so I don't think the different valves have any flow problems either.

[81xsproject]

Plus, at $33 for an entire set of 4 needles, seats, and screens, it is a pretty good price.

[GNEPIG]

I have just ordered me a set. What is your recomended float hight with these needles?

[81xsproject]

It should still be the same especially with the older round floats. I didn't have any issues at the stock height.

[egsols]

Hey 81xsproject,

I tried doing a conversion based on using the valves and floats from an 81 into a 79 using the 79 seats. I ran into the issue Ken was worried about, I had to bend the tangs so much that the they were binding on the valves. I see that you found a set that come from a XV920 so you use the new seats. Do the XV920 seats sit the valve lower so the plastic floats fit better?

I'm getting tired of trying to get a seal between the valves and seat on my 79. Already have gone through a new seat of aftermarket valves and seats that don't make a perfect seal.

[81xsproject]

The best set-up I have come up with is to buy these xv920 valve assemblies. With brass floats there is just barely enough room (what Ken was worried about). However, if you get some of the fuel resistant sealing tape (it is like teflon tape for fuel lines) and use a little on the threads of the seats, you can omit the use of the washer. This brings the height of the seat down ~1mm which is plenty. Both LVTom and cbradford have gotten carbs from me with the xv920 assemblies and no leaking from the carbs and I did both of those with the washers in. So, you don't NEED to go the tape route. As a side note, obviously you should make sure no tape is sticking out as it could come loose and clog something up. And to go to a further tangent, the tape can be use as a cheap fix for leaking fuel T's.