Motorcycle carbs flooding ... ?

[T i m]

Hi all,

Trying to help a mate with an old but cherished Kawasaki ER-5 (500cc twin).

Long short, as soon as you turn the fuel ('Prime') on it floods both carbs.

Now, I'm very familiar with carbs and float jets etc so I've done most of the usual stuff, and this is after the local bike shop has done the same for him and suggested it needs a pair of good second hand carbs (because the float valve seats may have worn oval?).

Now, it's only done 35k miles and the carbs seem in very good fettle generally (throttle butterflies neat and tight, slides run freely etc) and even with new float needles and the float heights set to stock (17mm) they still leak (out though one of the jet holes and the carb mouths). Even lowering the float heights to the max (19mm) doesn't seem to help matters?

If you take the cabs off, hold them the right way up and blow into the fuel line you can hear air passing though the jets and into the float bowls. That's good.

Turn the carbs over and blow into the fuel hose and you would explode your lungs before anything 'leaked'? That's also good?

Removing the float bowls and turning on the fuel sees the fuel pouring out though the float jets. Lifting the floats with your fingers to just the point where the (rubber) tip of the needle would touch the seat and the flow stops? Push harder and the spring loaded plunger in the back of the needle allows the float to travel further but the fuel is already off at that point anyway?

So, the only thing that doesn't seem to work is the floats turning off the flow of fuel when in the bowls as usual?

Now, the floats don't appear to have any leaks (and FWIW they both weigh the same at 8 grams), you can't see any fuel in them because they are translucent and don't *seem* to be in any way distorted where they might touch the sides of the bowls etc?

So, when the bike ran last it generally performed well on the road (and when it ran the few times today it sounded ok), the fault first showed itself by a raised tickover and it has been suggested that could have been fuel leaking into the crankcase (there was fuel in the oil) and vapour being blown back up into the carbs via the breathers and fuelling the engine that way (bypassing most of the carb functions etc)?

So .. I'm tending towards the thought that the floats have become distorted somehow and are sticking on the inside of the carb body / float bowl (when floating in fuel anyway) but I'm not sure how I would check that.

Or what else could it be?

It *could* be intermittent because we tested it after cleaning and calibrating by rigging up a temporary fuel tank and the carbs didn't flood at all?

Cheers, T i m

[Mark]

is ther sufficient fuel flow out of the tank shutoff device my triumph amal carb always starts to overflow when the in tank filter starts to block if both cabs are doing the same thing then unlikely that they suddenly both have the some fault

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[T i m]

Good question. The fuel tap is 'remote' and vacuum operated so there are 4 hoses. One the main tank outlet to the tap, one the reserve tank outlet to the tap, the feed from the tap to the carb(s) and a vacuum pipe to the inlet of one carb.

The tap has 3 positions, Prime (full on), On (main outlet enabled by engine vacuum) Reserve (reserve outlet enable by engine vacuum). There is no 'off' because without the engine running there is no vacuum on the tap and so no fuel (except in the Prime position).

So, to answer your question I'd say 'yes' as it both seems to allow the engine to flood pretty quickly (in any position) and filled a 5l petrol can pretty quickly on Prime with the outlet going to the can.

Oooerr?

Agreed ... and why I was asking here. ;-)

Googling around on the ER-5 bike it seems the symptom of sitting at

3000 rpm on tickover and flooding are both 'known issues', some of which are down to the fuel tap not turning off *and* the float jets not turning off (even with the bike parked and idle etc).

Apparently the 3000 rpm tickover issue can be related to a leaking throttle slide diaphragm but I'm less worried about that whilst we have the flooding issue whilst the engine is turned off.

Cheers, T i m

[harry]

Crap in the fuel tank/damaged/disintegrating/missing fuel filters can lodge in the float valve seats so causing leakage. Fuel filter usually attached to fuel shutoff tap inside tank..

When I was a teenager we used to grind float valves in if they leaked.

[T i m]

How often should we do that? ;-)

True.

Except this setup has a remote tap (so no tap fitted to the tank itself) and unless there is a filter inside the tap, there isn't one on there. We have spoken of fitting one but they can cause issues themselves (I fitted two on my BMW motorbike and had to remove them on the first trip).

These are rubber tipped so again, not possible in this instance. However, they are brand new (carb service kit).

It's very frustrating.

A float valve is the most basic of mechanical systems and on the bench, everything about these look perfect.

Further, with the basic 'blow into the fuel line and test the float valves the right way up and upside down (so the valves only being closed by the weight of the floats and jets) seem to demonstrate the things as working perfectly? Operating the floats manually whilst sat on the bike (with the float bowls off) also demonstrates they are working perfectly?

So it's looking like the (hollow plastic) floats aren't working properly when they are expected to 'float' (in petrol) but they don't appear to be punctured or cracked or have taken on any fuel (and at 8g weigh exactly the same).

Cheers, T i m

[Dan S. MacAbre]

Wouldn't you need to raise the float heights?

I had an Amal concentric on me old Tiger Cub, and that had a punctured float, but you've already checked that. I'd only add that the puncture was tiny, and you couldn't hear the petrol splashing about. The floats weren't clear like yours, though. In those days, there was a metal tab that you needed to bend up to make the adjustment.

Maybe the floats have 'shrunk' with age and become denser? Everything else (blowing in the pipe while they're upside down) makes it sound like they would be fine as long as the float lifted properly.

[T i m]

Yes / no, I think this is just a terminology thing Dan.

The spec says 17 +-2mm so 15-19mm. We initially set them to 17mm and that is really the *distance* (not 'height' as such) between the bottom of the float (when the carb is the right way up) and the body of the carb, when the float is dangling such as to *just* close the valve. So making that a bigger number will cause a lower fuel level (I believe). ;-)

The best we can Dan. Luckily the floats are hollow plastic, translucent and made of two 'sides', and neither side on neither floats are leaking that we can tell?

Yes, I have experienced that in the past, confirm we tested for that (sploshage) and couldn't sense any at all.

Same now days. ;-)

I'm at the point where I'd consider anything possible!

Precisely. The only issue I can think of with that test is that the weight of the (very light) floats when upside down in air may offer a grater closing force to the jets than the floats floating in petrol (but really)?

Apparently these Kawasaki ER-5's (and other makes and models no doubt) suffer with issues of the automatic (intake vacuum driven) fuel taps not closing fully / intermittently but I've only ever turned the fuel taps of my motorcycles off when I've finished using them that day, not because not doing so will see them flood? ;-(

Ok, I think the carbs on my old 'Airhead' BMW's have been know to flood but all that does is soaks your boot, not flood the engine / crankcase / airbox and a quick clean (and the float bowl clips on, making that a roadside job). ;-)

Cheers, T i m

[Dave Plowman (News)]

Dunno these carbs, but with SUs you'd tend to replace the valve and seat complete - it just screwed in.

Does the valve and seat look OK under a magnifying glass? If not, and the seat is part of the carb body, I'd be inclined to lap the valve to it.

Other thing is not enough lift from the float, or it sticking. But you seem to have covered this. I assume you can't just by new ones?

[T i m]

Yeah, same on many bikes Dave, just not this one.

I've not looked by daughter has (with her good eyes) but I should be able to get in there with an endoscope.

Except, these bike valves are often rubber tipped and so you couldn't really use the valve itself to do any lapping.

Well, sort of. I am wondering if the float upside down in air is the same (jet-sealing) effect as the right way up in petrol (buoyancy V mass etc).

No, you probably can but I'd hate to think how much. The throttle slide diaphragms on this model are ~£100 each. ;-(

One thing I have learned since posting is that you can put a small clear hose on the bowl drain nipple and run it up beside the carb. Then you crack the drain screw(s) open, apply fuel then you can see what the fuel level is in the carb bowl(s). ;-)

And that's fine of course, *if* it doesn't flood straight away! ;-(

Cheers, T i m

[Dave Plowman (News)]

Ah - of course. Think those arrived on later SUs too. I'd guess the rubber might wear or perish etc? No chance of buying new? Checked Ebay etc for pattern parts?

[T i m]

I think the classic failure mode for them is the develop a ridge where they sit on the hole in the seat.

New already fitted. ;-(

Cheers, T i m