Float Height/Valve

[PJSALERNO]

Happy Spring, all,
I'm rebuidling my carbs on my 78XS E, all new jets and such. All the parts I got match the old ones except the valve for the floats. The new ones have a lot less spring to it and brings the float hight way to high (low when upsidedown) I would need to adjust the tang alot to reach the desired 25.7mm (about 1") height. should I just use the old ones, they're on the money. My hesitation is that the main reason I am rebuilding the carbs is because #1 was leaking. I'm doing the petcocks too.

Also, I read on the forum somewhere that the floats should sit over 1/2 way out of a cup of gas when checking for buoyancy. All 4 of my brass floats sit only a about 1/5 out of the gas, with no sign of pin hole leaks. Is this ok?

I want to get everything back together today, fire it up and fine tune it. Any help would be great...Thanks...Phil

[MartyA]

Well it is tomorrow and I see no answers. How did you do?

I am not a carbie person, but I have a question about those floats. You said 1/5 is below the fuel line? Was that the old ones? How does that compare to the new ones? If they are the same then you should bend the tang. That is the way to control the fuel level in the float bowls.

That is an interesting thought, though. The procedure for float height adjustment does not take into consideration float differences. I have not taken my carbs off, so I do not speak from experience, but if you have two sets of identically shaped floats, but one set has more mass, the actual float height in the float bowl will be different for the two sets - lower for the heavier float set. That is why I asked about the new floats. Maybe this is not an issue, as I said I have never touched my floats, don't know if replacements are different from originals.

As much as I know, your leaking is likely due to the float valve not seating. If that is the case, your repair of the petcocks should stop this anyway. Replacing the old parts should also help.

Maybe this will stir the pot and a more experienced person will chime in.

[RiskyBusiness]

Well I will jump in here with a follow up question as well...

Did your rebuild kit include the actual floats? I ask only because all the rebuild kits I see include the float valve (piston-like thing), but not the actual floats. Is the length of the piston part of the valve different than your old one or is the float all that is different?

The distinction you made about how deep in the gas different floats settle is why I decided to balance my floats using the tube method. I eye-balled things first then tweaked with the tube. I didn't trust my ability to get it right without actually testing how high the fuel level is.

[PJSALERNO]

The kit didnt come with the floats, but the valves did come new (which I didnt use).All 4 floats had the same buoyancy when placed alone in a cup full of gas. Maybe the difference is in the posts where the float pin goes or the pin itself, (it looked ok) I'll try the clear tube test., More later...Thanks

[MartyA]

PJ, if your carbs are original on your 78 you can't do the tube thing. That little outlet on the bottom of the float bowl comes on the 80 and up if I remember correctly. Wish we could do the tube thing, though.

[Bob Falter]

Marty is correct. The 78 and 79's just came with a plug in the bottom of the float bowl, nothing to hook a tube to. Thought about making some kind of fitting to get the job done but mine bike runs great after just setting the float height, and I set it too low (will run the gas level high) by 1.6 mm. If I can be that far off and still have it run good why bother with the extra work? Now if I can just get them to stop leaking.

[lewis]

Hey Guys:

Been a while since I've been on the site.

PJ, I've done alot of work rebuilding my carbs from the ground up because they were completely gummed from years of non use. This is what I have found.

Use original yamaha jets, especially your idle jets. the aftermarket ones I got were not right even though they were marked the same. they ran way too rich.

as far as the floats go, if they all float the same level and they don't have any fluid in them, you can tell by shaking them, then they are ok. I set the measure height as per the manual. To check, since I have a 78 and can't do the tube thing, is I mount my carbs on a verticle board using 1" L braces and hose clamps so they are level, feed them gas from an auxiliary tank like the ones used when you sync the carbs on the bike, shut the gas off, and then drain each bowl, measureing the amount of gas. you have it right when they all are the same or pdc.

If you build the carb stand, you can also test that the float valves don't leak by gassing the carbs up and letting them stand for a while.

[beechfront]

lewis - i cannot believe nobody has posted that as a way to test float height. sooo simple. i will be using that method from now on.

thanks.

[schpiff]

it is possible to "fix" the rubber tip on the needle..find yourself some real fine sandpaper/emery cloth and lightly scrub the old needle rubber. It has to be real fine as to not dig in too much.
If all your floats are consistant then you have no prob..its probably just the rubber tip on #1.

[nashville_bill]

You can buy the needles from PartsnMore for $2 each. I have an extra four of them just waiting for problems. They fit my XS650 also.

[RiskyBusiness]

Originally posted by schpiff
it is possible to "fix" the rubber tip on the needle..

Does the 78-79 have rubber tips or did that start in 80? I was thinking that some of the early ones did not have rubber tips.

[PJSALERNO]

U R correct RiskyB, no rubber tips on 78E.