Carbs Overflowing - Think I've Fixed It

[nick307]

Morning all,

The carbs on my 2005 Bandit 650 have an intermittent issue where if I've left the bike for too long without taking it for a ride, it starts to piss fuel out of the overflows onto the floor (I'm taking that as a sign that I need to get out more). Sometimes this lasts a few minutes and a good shake fixes it, sometimes it lasts 20 miles of back roads to work, and more recently, it started after heavy braking down from 60 for a red light camera. Sometimes it's out of 1&2, sometimes its 3&4, not had both yet though...

I've come to the conclusion that it's something to do with the float needles getting stuck (duh) so I had the carbs off last night to have a poke about.

I've had the carbs off a few times to clean the jets out as when I got the bike it wasn't running at all on #1, but in my ignorance I never bothered to look at the floats or the float needles.

Once the needles and floats were all out and on my work bench I had a look at the brass housings the needles fit into, and unsurprisingly they all looked pretty crap... dull, dark brown, not very nice. #1 (left) looked the worst of the lot, which I think is something to do with the fact that the bike no longer has a center stand so has probably spent most of its life leaning over to the left.

The brass parts I polished up using some autosol, q-tips, and a drill, and they all came out absolutely beautiful. I soaked them and the fuel inlet piping in some hexane degreaser (because my chemistry PhD girlfriend says that that stuff should be the tits for getting rid of petrol deposits and just about everything else) and blew them out to make sure there wasn't any residue from the polish left in there, then moved onto the needles.

More autosol, more q-tips (gonna need to buy a new tub or she won't be happy!) and they are all clean. If you've ever polished any oxidised metal before you'll know what I mean, but the needles just felt a bit gritty for a few seconds whilst rubbing in the autosol, but after maybe 5-10 seconds in each area the autsol went grey and the area I'd been polishing started to feel a lot more smooth and lovely!

Carbs cleaned and reassembled, they went back on the bike. A few seconds of cranking and it all fired right up again, and a quick ride to the nearby Shell to add some more gogo juice.

So far it's not had any more incontinence, but if it does, I'll have to have another look at the carbs... oh joy...

Other things to note:
- the floats were all empty (no ingress of fuel),
- the floats were all sitting exactly inline with each other when up and down,
- fuel filter is looking completely clean,
- before I got it in march, it had done 50 miles in 9 years, since then I've done 2000 miles on BP/Shell's finest go faster juice

Hopefully this works for me, and might help someone else who's having similar issues!

If it doesn't work, do any of you have any suggestions of where I should look next to try and track down my problem?

Ta
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"Nothing is impossible with the right attitude and a hammer!"

[RhynoCZ]

The next time your carburetors leak from the overflow, knock them with the end of a screwdriver, to get the float valves seated properly. It is odd though, that this happens after you leave the bike sit for a while. That would tell me those float valves leak very slowly but constantly, or there is a completely different issue. But, as you mention 50 miles in 9 years, I bet my money on petrol crud.

The XBR, that I recently bought, has a filthy carburetor (no time to clean it now). When I rode it at constant high speed = very high fuel flow, the float valve got into a position, where it doesn't get often and got stuck on all the ''modern petrol'' crud. It got stuck fully open, so when I got in front of my garage, it left a nice puddle of petrol on the ground. It leaked in a rate like if I just took the fuel hose to the fuel tap off and turned the fuel tap to RES, that's how quickly it was loosing fuel.

Petrol off + a few knocks on the carburetor bowl area = float valve drops and starts doing its job again. This is a roadside repair option, by the way.
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'87 Honda XBR 500, '96 Kawasaki ZX7R P1, '90 Honda CB-1, '88 Kawasaki GPz550, MZ 150 ETZ
'95 Mercedes-Benz w202 C200 CGI, '98 Mercedes-Benz w210 E200 Kompressor

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It just means the float valve isn't seating properly into the cup to stop fuel flow. Three main reasons, firstly that some debris is sitting in the cup blocking it from seating shut fully. Secondly, if the bike is getting on a bit, the cups and valves wear and won't make a good seal (you can see a ring around the float needle), thirdly and less likely is a float getting stuck, at the wrong height or the float itself is leaking and taking in fuel.

I used to put inline fuel filters to reduce float issues and also replaced the valves and cups on some of my older 2 strokes.
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TZR250 2MA road, TZR250 1KT road, TZR250 2MA race, TDR250, YZF-750R Boost colours.
Jaguar S Type 3.0 V6 Sport R, VW Transporter T5 GP LWB Shuttle 140ps DSG.

[nick307]

If in doubt break the hammers out!!! I've got a small adjustable stashed away in my repair kit for just such an occasion! I'll add "percussively re-seating carb needles" to the list of 101 things you can do with a shifter that aren't tightening bolts.
____________________
"Nothing is impossible with the right attitude and a hammer!"

[jaffa90]

Does this bike have a vacuum operated fuel tap?
Also the needle valve rubber tips go hard after years.

[nick307]

Yeah, it's got a vacuum operated tap. Seems to be letting the fuel through no problem though, as it's letting a bit toooo much through!

I had a loot at the rubber caps and to be honest they all looked alright. There was no ring around them from the carb body, and whilst they weren't exactly soft, they were easy enough to press a fingernail into gently (didn't leave any dents though so all good there)

A new needle kit is only a few quid though so that's a potential for next time if it continues to make a mess.
____________________
"Nothing is impossible with the right attitude and a hammer!"

[jaffa90]

"""""Yeah, it's got a vacuum operated tap. Seems to be letting the fuel through no problem though, as it's letting a bit toooo much through! """"

Fuel should not flow with the engine stopped, unless you have a PRI positioned tap.

[nick307]

Sorry, I wasn't particularly clear there... The tap seems fine. Lets fuel through with the bike running, didn't let a drop out when the tank was off last night.

It doesn't have a manual switch, its just on or off depending on the vacuum / no prime setting.
____________________
"Nothing is impossible with the right attitude and a hammer!"

[RhynoCZ]