Non plastic floats buoyancy testing??

[Fentible]

Had this 1980 XS 400 SG5 running beautifully last year after eventually sorting a 4000 RPM misfire. Started easily, ticked over steadily but over the winter layup, it drained the contents of the petrol tank into the engine. This despite the petcock and carbs being rebuilt with new seals and float valves respectively.

So, got rid of the original vacuum tap and replaced with a Mikes XS manual tap. Carbs still flooding slightly though, causing poor starting and an inability to maintain tickover. Switch the petrol tap off with the engine running and as soon as the fuel level drops slightly in the float bowls the bike ticks over happily until it runs out of fuel. Float heights at 26mm, float bowl breather clear, replaced float valves again just in case, hook the carbs up to a fuel supply on the bench with a funnel, mark it after the initial float bowl fill and the fuel level slowly drains down over a couple of hours. I can see fuel lying at the top of the jet needle, but it doesn't flood out. Tried various float heights to exactly the same result, although I haven't tried the Haynes manual recommended 32mm as I'm led to understand that it is a misprint.

If I orient the carbs as if on the bike, remove the float bowls and add fuel, I can easily control the flow with really light finger pressure on the floats. So the float valves work fine. I have thoroughly checked clearances and the floats are definitely not hanging on anything.
These carbs have the black rubber style floats and although they float, they do so with about 95% below the petrol level. Am I right in thinking that they can lose buoyancy? I don't have a new one to compare with,they are expensive so don't want to shell out unnecessarily, but I'm totally out of ideas/options
Any thoughts from the collective??

 

[MrStubb]

I'm not so sure if this would help but I believe there is a specific weight for the plastic floats. And if they're slightly heavier they will allow your fuel level to be too high & possibly cause your flooding issue. If you can find a set of brass floats from an 79 or earlier you may be able to fix the issue. Some of the non metallic floats have soaked up fuel similar to a sponge. Usually caused by ethanol breaking down the coating that protects against this problem.

 

[Fentible]

I'm sort of hedging towards the floats as an issue, as I say the bike an perfectly till it was laid up for the winter and unfortunately without draining the carbs. Googling the float weight has not come up with any results and I agree that the older type brass floats are likely to be a better bet but come in at even more than new black rubberised ones.

 

[BBS360]

I've seen more experienced members state that floats/float valves are fuel metering devices, not fuel shutoffs.
Turning a manual fuel tap to "off" is the only way to definitely shut off fuel flow.

Doesn't work so well when the vacuum petcock is also leaky....

 

[xschris]

Plastic float height is not the same as the brass ones. Those are 22mm I do believe.

 

[MrStubb]

Plastic float height is not the same as the brass ones. Those are 22mm I do believe.

I believe you're right Chris. Chris do you know when they started using the plastic floats?? The 80 that I just picked up is about 600 in serial # after my other bike but it has the brass floats where mine had the plastic ones. A curiosity!!!

 

[xschris]

81 was the first year for them. But after many years and owners stock carbs get to be non-stock. I have sold a lot of 81 carbs with brass floats over the years. Just because I prefer brass over the foam ones.

 

[Fentible]

So in your opinion Chris, can the foam ones lose buoyancy?

 

[xschris]

No. I have never seen one that has.

 

[Fentible]

Hmm..........any ideas on what else might be causing fuel to seep past the float valves??

 

[16VGTIDave]

The float valves are defective, or the floats are not adjusted correctly. Have you checked the fuel level in the float bowls with the bike on it's wheels, on level ground? The measurement technique of setting the floats is only applicable to 100% stock bikes. If the ride height has been changed, then the actual fuel level has to be verified. It MUST be below the float bowl gasket, or flooding / running rich problems will occur. Believe me when I say that I learned this the hard way...

 

[Fentible]

Float valves brand new (needle and seat). I have tried varying float heights to nil effect. Bike was running superbly prior to winter lay up.

Floats themselves are the only thing that hasn't been renewed

 

[MrStubb]

I've seen floats soak in other applications with detrimental effects. Mostly in vintage boat motors lawn mowers & several small military engines I have in the garage. Most are of a different material than those in our bikes but the effect is the same.

 

[16VGTIDave]

Float valves brand new (needle and seat). I have tried varying float heights to nil effect. Bike was running superbly prior to winter lay up.

Floats themselves are the only thing that hasn't been renewed

I'm not going to argue with you. New does not guarantee functional. You have told us that the float valves are either not sealing, that the floats aren't floating, or that the fuel level is set too high.

What more can we do? You've been offered tests and possible solutions. You have to choose to act on the advice, or not.

 

[Fentible]

I'm not going to argue with you. New does not guarantee functional. You have told us that the float valves are either not sealing, that the floats aren't floating, or that the fuel level is set too high.

What more can we do? You've been offered tests and possible solutions. You have to choose to act on the advice, or not.

Seriously......... " what more can WE do?"........... You need to chill out mate..............no none is arguing with you. I have undertaken all the tests and tried the possible solutions to nil effect. Perhaps you should read my original post more carefully and stop assuming that you think you know what is wrong??
Fuel stills seeps past the float valves regardless of what I try (2 x new sets.........yes I also believe that new is no guarantee of functionality) and I was simply asking if people thought that the rubber style floats can lose their buoyancy.
Thank you XS Chris and Mr Stubbs for your more considerate advice.
Honestly, "what more can we do".....................best laugh ever.

 

[16VGTIDave]

Quite the cheeky attitude from someone who should have their hat in their hands. I understand that you are frustrated, but that is no excuse for poor manners.

This despite the petcock and carbs being rebuilt with new seals and float valves respectively.

So, you rebuilt the petcock and it flowed fuel when it shouldn't have. You rebuilt the carbs and the fuel level is too high and floods the engine. When I suggest a test that would answer your questions you tell us what you have already done, that it hasn't fixed the problem, and you completely ignore my suggestion. The work you've done, and it's quality, is not being questioned. That has been well established, by your own admission.

Now, go find some clear fuel line and verify the fuel level in the float bowls as previously suggested. Then report back with your findings. We'll be here to help.

 

[Almost_Infamous]

Plastic float height is not the same as the brass ones. Those are 22mm I do believe.

Sure wish I saw this last week

 

[PEPXS400]

If it was me, I would go to ebay and buy some brass floats. If that doesn't fix it, then you might have to pull them partially apart and clean that passage good. Maybe try that first before buying. Just one small piece of varnish could be sticking in the bottom and not allowing it to seat. Also if someone cleaned it before with an abrasive tool, they could have gouged it and the new parts are now not seating correctly.
We all are here to help a fellow XS rider! Be kind and rewind

 

[Fentible]

Quite the cheeky attitude from someone who should have their hat in their hands. I understand that you are frustrated, but that is no excuse for poor manners.

.

Actually, I thought it was fairly restrained, I usually struggle with the intellectually challenged. You may also want to reconsider the post I reacted to and how it came across before you accuse anyone of poor manners. You were totally intolerant, judgemental and condescending. What did you expect, respect with that ill mannered response??

Okay. I'll be the first to admit I don't always grasp the concept but please explain to me the value of using plastic tube simply to verify that the carbs are overfilling? If I was actually trying to ascertain the correct fuel level, I could understand the rationale. But as the fuel level just keeps rising until it overflows, I'm not sure what I would be reporting back. Did you actually read my original; post or perhaps you found the long words confusing?.


PEPXS400: Thanks for your suggestion. I didn't just replace the needle valve I replaced the entire needle valve assembly........twice. Just to rule out a possibly flawed pattern part, so I know they haven't been messed with. I'm also using a clean fuel source through a filter so I know its not residual dirt causing the float needle to unseat. I agree that the brass floats would be the way to go and I'll probably follow that option next and report back.

I also appreciate the value of forums like these, I subscribe to several and enjoy a good humoured exchange of ideas. What I don't appreciate are narcissistic idiots who think they know everything, really don't and lack the fundamental of good old fashioned courtesy.

 

[xschris]

Put your foam floats in a cup of water to test them. If they float it's not them. Are you setting the float level without the bowl gasket in the carbs? They should be removed for accurate measuring. There are threads on where to measure from and the part of the float.