Mikuni BS32SS Flooding issues (Cannot figure it out!!!)

[Guest]

Ok guys, this is making me pulling my hair out!

I have this set of 4 Mikuni BS32SS carbs that I have to clean out for a guy, they all flooded so I checked the float needle and sure enough they all had wear marks.
Of course I have replaced both the needled, the seat and the O-ring, I reused the filter, also I set the float height to 22.4mm as per manual.
The weird thing is this will work perfectly well if you test this on one carb (all 3 other valves shut) however, when testing the same thing with two or more carbs connected the whole assembly starts to flood.
I made a little plug to connect to the bottom of the carb so I can connect a clear tube to check fuel level, this is correct for every single unit except when connected together.
For me It is impossible to figure out why it leaks! the needles are obviously working, It's not leaking past the O-ring otherwise it would leak when testing the carbs individually!

When it start flooding it seems to be coming from the little opening on the opposite side of the air jet in the intake bellmouth, but soon after that it just comes from everywhere.
The carbs have been thouroughly cleaned (ultrasonic, compressed air), and new O-rings and gaskets are used.

Any help would be greatly appreciated! I have done many many carbs I do not understand what is happening here

[BillH]

Hey Bud,
Yeah that sounds weird. Works with one but with more than one connected if floods. Is this with some sort of bench testing your doing with fuel ? Or are you connecting them to the engine and watching the flooding that way ? I did notice your mixture screws were turned way out.

[Rensdw]

Hey Bud,
Yeah that sounds weird. Works with one but with more than one connected if floods. Is this with some sort of bench testing your doing with fuel ? Or are you connecting them to the engine and watching the flooding that way ? I did notice your mixture screws were turned way out.

I bench tested and tested with a running engine, the engine starts up just fine and dies when it floods, the screws are turnied 2.5 turns out here, the manual says 2 and 1 quarter but I'm not too worried about that yet.

[Spyderman]

is it leaking down the vacuum tube into the carbs from the petcock???

[Rensdw]

is it leaking down the vacuum tube into the carbs from the petcock???

Nope, during the benchtest the vacuum tube is not connected to the carbs.

[850GT_Rider]

How high is your fuel source above the carbs? Once, with the tank off and using a bottle hung from the garage rafters, the resulting head pressure was enough to overcome the float needles. Dumped fuel all over the ground. Dropping the bottle down to just a few inches above the carbs (duplicating the elevation of the setup when the tank is on the bike) stopped the flooding immediately.

There are those here in the forum who will scream BOGUS! and say that the elevation of the fuel source has no effect. All I know is what I experienced.

And just a reminder - without the petcock attached, the vacuum port on the carb must be plugged.

[Rensdw]

How high is your fuel source above the carbs? Once, with the tank off and using a bottle hung from the garage rafters, the resulting head pressure was enough to overcome the float needles. Dumped fuel all over the ground. Dropping the bottle down to just a few inches above the carbs (duplicating the elevation of the setup when the tank is on the bike) stopped the flooding immediately.

There are those here in the forum who will scream BOGUS! and say that the elevation of the fuel source has no effect. All I know is what I experienced.

And just a reminder - without the petcock attached, the vacuum port on the carb must be plugged.

Thanks for the input, I am going to try that tommorow, I have like a meter long test hose connected to the fuel tank and the carbs are laying on my jacktable right beside the motorcycle.
Although I have had the carbs mounted to the engine but that was before setting float hight, I"ll try again!

Regarding the vacuum port, leaving it open with the engine running will make just one cilinder run bad so not really relevent here, I'm trying to get it working during the benchtest first anyway.

[geol]

Two things... sounds like someone had previously bent the floats for adjustment incorrectly and although you are seeing
22.4mm measured, the actual position of the floats is allowing the carb(s) to flood; Suggest you get a 1/4" straight piece
of plastic vacuum connector (sold in auto parts store) and thread it into the drains of each carb in turn and ensure the
fuel level is about 3mm below the gasket mating line. That can often cure this type issue.

The other issue may be the carbs are not venting. There is a tee vent between 1 & 2 and 3 & 4. Check to see that air
flows from inside the upper bowl chamber through the vent on all carbs. If a carb isn't venting (such as the vents are
capped) the floats act crazy and will either spew gas or not flow much at all.

[Rensdw]

Two things... sounds like someone had previously bent the floats for adjustment incorrectly and although you are seeing
22.4mm measured, the actual position of the floats is allowing the carb(s) to flood; Suggest you get a 1/4" straight piece
of plastic vacuum connector (sold in auto parts store) and thread it into the drains of each carb in turn and ensure the
fuel level is about 3mm below the gasket mating line. That can often cure this type issue.

The other issue may be the carbs are not venting. There is a tee vent between 1 & 2 and 3 & 4. Check to see that air
flows from inside the upper bowl chamber through the vent on all carbs. If a carb isn't venting (such as the vents are
capped) the floats act crazy and will either spew gas or not flow much at all.

Thanks for you input, I have adjusted the floats with the method you describe, so that can't be it.
Today I will surely check the vents, thanks!

[Rensdw]

Ok guys I seem to have fixed the problem, I clean the float needles again and I noticed the gas coming out of the fuel tank was dirty so I replaced the gas after cleaning the fuel tank.
It still wasn't fixed but then I raised the carb assembly up higher as 850GT_Rider said and that did the final trick.

Now the bike doesn't wanna start but I suspect the coils are bad since there is a very weak blueish spark, but that's a separate issue

Thanks!