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Are my float valves bad? opinions please...

Wallowgreen

Wallowgreen

Forum Mentor
Past Site Supporter
I'm having real problems setting the float levels in the VM carbs on my 79 850. I set them to spec then refitted them to the machine. After a while (days - which makes me assume the issue occurs only with the engine running) there's gas seeping from the float bowl gaskets.

I took the rack off the machine and cleaned them up again, now I'm trying to set the float levels so the gas level is correct and would like to get it right this time. I'm quite willing to replace the float needle valves and seats on all four but want to avoid the situation where I spend the $130 for OEM parts, which seems to be the recommendation, to find I still have the same problem.

To that end, I've taken my existing valves and seats to the microscopy lab at work and have some pictures of the valves and seats. I see some marking around the needle tip but it doesn't seem to have scored the metal at all far less worn a shoulder so is this just where the valve has mated with the seat? It seems logical to expect some marks where the two surfaces come into contact, in fact I could believe some wear might be expected so the surfaces mate even better.

What do you guys think, do they need to be replaced?


#1 needle
FloatNeedleValve4001.jpg



#2 needle
FloatNeedleValve3001.jpg



#3 needle
FloatNeedleValve2001.jpg



#4 needle
FloatNeedleValve1004.jpg


Needles and seats are at:
http://s612.photobucket.com/albums/tt209/wallowgreen/VM Float Needle Valves/?albumview=grid

Thanks.
 
Well I bet on one on here has ever seen them as close up as that! Great photos. They do look worn but as I've never been able to see that close up before I wouldn't be able to tell if they were badly worn or not.

I do 2 tests:
First get the seat and pop in the needle. Applying the same pressure as the floats could do, hold the needle in the seat with you finger (sure, it's a pretty inaccurate guess) and try and blow through the hole. If it's easy they're suspect, if your cheeks bulge out they're better.

Second, rebuild the carbs and pop them upright in a vice or workmate. Pour some petrol down the fuel pipe and see if there are any leaks. If there are, replace before refitting to the bike.
 
If fuel is flowing while your engine is shut off, you need to look at the petcock, not the float needles.
The floats and their needles are designed to control the rate of fuel flow to keep the fuel level constant when the bike is running, they are not meant to be shut off valves.
That's why bikes have petcocks.
 
Last edited:
I'm not usre if VM series carbs have o-rings on the float seats or not. If they do the fuel could be getting past them even if the needles are sealing up properly.
 
The sealing area of the needle valve looks fine.

how is the spring/ plunger end? sticky? are the springs weak?

put the needle and seat back in, put the float and float pin back in and turn the carb bodies so the floats are hanging down, then turn the carbs bodies until the float just rests/contacts the plunger on the end of the needle (without compressing the plunger)... then measure the float height on both side of the float.

adjust float(s) as necessary.
 
After checking Alpha Sports I see the VM carbs use a gasket on the seats. How do the gaskets look?
 
Sorry should have given a bit more background...

Just a couple of months ago I stripped, dipped, fitted new o-rings, seals and gaskets everywhere so the gaskets on the seats are new and I assume good.

The petcock was replaced about 6 months ago with an OEM one. With the tank off the bike for the last week and there being no spot under the petcock I assume the petcock is not leaking.

rustybronco, the spring force is a question in my mind too. Sadly I have nothing to compare with to even guess if what I have is weak or not. They may have been changed out for aftermarket (i.e. weak) one's before I got the machine. Even if weak though, I should be able to find some float level setting that compensates... shouldn't I?

Hampshire, I've tried your blow through test with confusing (at least to me) results but came down on the "they're good" side. In the end I put each individual carb back together, leveled them with a plastic tube shoved in the drain hole wrapped up around to the top of the body then poured petrol into each one in turn with the floats set at spec. All had levels that seemed too high compared to the 3-5mm down from the bowl mating surface shown in the pictures in the manual. So I set about fiddling with the float settings to get the petrol level 3-5mm down and have been fiddling ever since. Seems every time I test them I get different result and that's why I started to question the needle valves again.

Electrics are much less frustrating!
 
Wallowgreen said:
The petcock was replaced about 6 months ago with an OEM one. With the tank off the bike for the last week and there being no spot under the petcock I assume the petcock is not leaking.
Click to expand...

And yet there is fuel leaking when the engine is shut off...
Leave your floats alone, it's the petcock.
 
tkent02 said:
And yet there is fuel leaking when the engine is shut off...
Leave your floats alone, it's the petcock.
Click to expand...
No disrespect intended, but it may be leaking elsewhere.

a few more comments if I may...

(1) are you sure the fuel is coming from the gasket area? if it is coming from that area then it could be a bad gasket and/or a bad surface on the body or bowl.
does the gasket show the markings of complete sealing on both sides?

(2) does this issue occur with the bike on the side stand, or does it also occur on the center stand?
with the bike on the side stand the fuel level is parallel with the ground possibly making the fuel higher than the gasket sealing surfaces.

(3) have you tried connecting the fuel line from the tank to the carbs, putting the petcock on prime and mounting the tank about 1 foot higher than the carbs?
does it leak with the carbs mounted the horizontal and inclined position as when on the side and center stand?

(4) spray foot powder on the offending area and check were the leak(s) is/are actually coming from.
are you sure it's not the fuel tube, or some other place such as a crack?

(5) does the leak occur with the vent tubes disconnected?

(6) how far does the float travel from where it just contacts the needle plunger, to where the full weight of the float is resting on the needle valve as a percentage of travel. I would think (read guess) 25% further is about the most it should travel. I can check the (honda and yamaha) carbs I have on the bench if you need me to.

no more thoughts at the moment.
 
Last edited:
tkent02 said:
And yet there is fuel leaking when the engine is shut off...
Leave your floats alone, it's the petcock.
Click to expand...

Nope, don't believe I said that. In fact I said or meant to say the opposite.

Perhaps it would help to clarify a little. After a few days gas is evident running down the outside of the bowls from the gaskets I believe because the fuel level in the bowl is too high then drips from the drain plug onto the engine casing. It seems to stop because if I clean the bowl and drain plug it doesn't happen then until after I ride it again.
 
Wallowgreen said:
I believe because the fuel level in the bowl is too high then drips from the drain plug onto the engine casing...
Click to expand...
I.E. out the over flow tube in the bowl? how much does it drip?
there should be drain hoses connected to them.
 
rustybronco, thanks for the suggestions, some thoughts come to mind...

The gaskets do look to seal ok, they all have the tell tale line in them from the bead running around the surface of the body. However, the original philips head bowl screws were pretty boogered before I even got there. This time I've replaced them with allen head bolts and new spring washers. The reason I think the fuel is escaping from the gaskets is because there's no evidence of fuel on the body itself, only generally on the bowl but right up to the top surface.

The problem has only been noted on the side stand as I rarely use the center stand. And you know what, I think the bowls were only dirty on one side, the downward side. Hmm, interesting, I'll remember that when I eventually put the carbs back on.

As for the other suggestions...

connecting the tank back to them before refitting the rack was something I'd considered but haven't done yet. Perhaps I'll try that this weekend.

Foot powder is a new one but I'll try that also if/when it happens next.
Not measured the float travel, I will tonight.
I don't know if the leak happens with the vent tubes disconnected, I'll bear that in mind also.

Thanks again!
 
rustybronco said:
I.E. out the over flow tube in the bowl? how much does it drip?
there should be drain hoses connected to them.
Click to expand...

No, don't think from the over flow tube in the bowl. All have the drain hoses connected down to the ground and there's no sign of fuel dripping from those.
 
rustybronco said:
then what do you mean by drain plug?????????
Click to expand...

The drip is from the bowl drain plug.

Wish I'd taken a picture now that would have been best but it looks like fuel runs down the outside of the bowl to the bowl drain plug then drips on to the engine casing.

Think you may be on to something with the sidestand comment though. Just maybe I couldn't tighten the bowl screws enough on the gasket and that's all it is. Hope it's that simple, can't seem to find much else wrong.
 
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