B400 '91 - cylinders full of fuel - time to time

[ventYl]

Hi all,
the common problem - while trying to start I've found that one cylinder is full of fuel. Nothing impresively interesting, worn/dirty/stuck float needles and/or fuel tap. The problem is that while I've had similar problems for maybe month ago and I did complete disassembly / cleaning / reassembly / set-up and ballance of carbs. The O-rings in float bowl assembly and under top cap are all new.

While the carbs were disassembled I flushed all the internals with all jets and needles removed with special care for thin passages. I've also examined needles for any wear. Nothing even close to illustration in workshop manual but while I have one spare set of needles which sealed perfectly I swapped one float valve which was visually the worst. There was no crack, dents or deformation in rubber but there was visible ring on the rubber at the place where needle touches the seat.

So current status is that all four float valves are cleaned, fuel line is all new straight from fuel tap to carbs, carbs are cleaned and still, time to time some of cylinders is filled with fuel. There's no apparent corellation to time, weather, amount of fuel in tank. Sometimes cylinder is full after 8 hours of standing on burning sun, sometimes I can leave the bike sitting for almost week and it will start ok.

For the fuel tap. When the tank is removed it is sealing. I can have the tank laying around for days without single drip of fuel but if I am manipulating with it (moving over to another place and so) fuel is dripping slowly. I assume that this is wrong and may lead to dripping the fuel into fuel line where bike is standing. I have already ordered new OEM tap but it will take some time to arrive.

So now when everything is almost new the last thing I am suspecting to lead to stuck float valve is float assembly. Inner wall of cylinder where needle moves has scratches made by needle. The question is if these scratches can cause needles to become stuck (ofc I was trying to stuck the needles out of carb with no success) thus if someone had similar problem and float assembly replacement solved it.

[Squishy]

Ok so you put the bike away after riding, and when you come back it's flooded? How do you know?
How do you know it's not flooded after you tried to start it?

[ventYl]

After the engine was flooded for the first time I kept the bike half-disassembled so I was able to quickly rip off fuel tank and air box to see if intake manifold is dry and for one or two times I found fuel in manifold.

The last time engine did maybe one full turn and then stopped revving. Fortunately battery and starter are not powerful enough to bend anything

[Squishy]

Ok well I can't think of any way for the cilinder to get flooded to the point of hydrolock while sitting that is not related to the float mechanism or the fuel petcock.

[ventYl]

well that makes sense. the question is if in case that needles does not seem to be worn there is possibility that they became stuck. and another question is if wear of float assembly walls where needle moves may cause this. workshop manual mentions that if needles are worn out they have to be replaced by new ones. but no checking of float assembly is mentioned.

the problem is that aftermarket set of 4 needles can be obtained for around $50 while single OEM float assembly with needle costs $80+ per carb which is quite expensive right now. i want to avoid the case that I buy new float needles and the problem will remain because of wear at some other place.

[Gouraami]

I had the hydro lock issue recently, after opening the suspect carb I found a small piece of dirt inside the float assembly where the needle is (this was after I had cleaned it a few days before). Cleaned it out (again) and it his been 100's since.

I am running with a filter, so not sure where the dirt came from, could have been stuck in the fuel line somewhere

[Squishy]

I am running with a filter, so not sure where the dirt came from, could have been stuck in the fuel line somewhere

What filter are you using?
I've found most don't work without fuel pump

[Gouraami]

I found it at a car spares place. It is long and cylindrical. It seems to have a high enough flow rate, tested it with a smaller fuel can, but if it is high enough I don't know yet, will only be able to see once I can take the bike for a long high speed run (Still going to be a while from now). It is going to be a tight fit under the tank, but it looks like it is going to work.

[greg737]

while single OEM float assembly with needle costs $80+ per carb which is quite expensive right now.

I can send you a float assembly (just the plastic part, no needle) if you want.  I'm slowly giving away all the bits that I had left over after my fuel injection conversion (I already gave the needles to another forum member, Tonis).

[ventYl]

I had the hydro lock issue recently, after opening the suspect carb I found a small piece of dirt inside the float assembly where the needle is (this was after I had cleaned it a few days before). Cleaned it out (again) and it his been 100's since.

I've checked for dirt in float assembly as well. Found nothing. Actually something similar to hair was in assembly of another cylinder which was not leaking. Right now I've re-assembled carbs with mix of two different float assembly sets from two different bikes. Both used but I had enough luck to be able to get together one set of not-so-much scratched assemblies. They are currently filled with fuel off the bike to see if any of them starts leaking. Not much representative to normal use... but at least I'm trying :).

greg373: If you have no use for them we may try to figure out how much the postage will be. I assume that while I am in central europe and you in US (just a guess) the postage will be high. I'll send you my ZIP code via PM. I'll surely find use for them one day while I have another bike with the same carbs :).

[Gouraami]

Once assembled, I normally  turn the carbs upside down and blow and then suck as hard as I can into and out of the petrol inlet pipe to test if any of the needle and seats or o rings are leaking

[ventYl]

I am pretty sure that nothing else than needles can be leaking. I've tried to blow into fuel inlet pipes that hard that my eyes started to going out of my head :) this quite extreme pressure caused to raise the level in all four carbs (measured by clear plastic pipes connected to drain tube at the bottom of carb) by one centimeter... in all four carbs evenly.

I've been riding it today. With newly re-assembled carbs it runs pretty nicely. While flooding is only occasional I have to wait if it returns or not :/ Hopefully new petcock will arrive before next flooding.

[ventYl]

Report after few weeks: It looks like the petcock was the only one guilty in this case. After dismounting it from tank i've found that petcock was leaking the more the less pressure was applied so with low fuel level in tank and fuel inlet connected it was technically open.

Now with new petcock the problem is gone. Greg sent me his assemblies but while they are in same condition as mine I won't be swapping them. I'll be looking for some available replacement needles as current ones won't last forever.

[Gouraami]

Glad you got it sorted, the needle and seats must be worn though

[ventYl]

Well, seats seem be in condition similar to one's greg sent me. So either his were worn out too or neither mine and his are worn out. If I find out which needles are the correct one for this particular type of carbs I'll get one set and replace them.