82' GPz 750 BS34 float issues - dies at 5K rpm

Bike ran fantastic last summer, and after some issues this summer getting it going, it's now running great up to 5K and they it dies. Carbs are clean as can be, diaphragms excellent, and slides are smooth. Plugs are new, and I'm sure it's flooding out.

I've narrowed it down to the float levels, but no matter what adjustment the float has, the level is always too high. (using the clear tube method) Bike is now set with the level as low as the float tang allows, but it's still just under the bowl flange / seam. When it's set to the 18.6mm spec in the manual it's higher than the bowl mounting seam.

I suspect the black plastic floats aren't floating as they should, or the that the float needle assembly deteriorated over the winter.

Has anyone run into issues with the black plastic floats not floating? Or does it make more sense that it's just the float needle valve assemblies?

I'm hoping to get some confirmation of one or the other before ordering up replacements from Z1.

Bike only has 9800kms on it, and last summer it was running fantastic. Had the bike painted and the seat recovered over winter and now I have this running issue to fix before I can really enjoy it.

Any advise is much appreciated!

Rabin

Some thoughts where all 4 cylinders are simultaneously flooding ---

Partially blocked air filter under the seat (shop rag, gloves, or such).
Dirty or over-oiled air filter.

Floats installed upside down.

Low battery or imperfect cable connections.
Would verify voltage reaching coil is 12-13Vdc with engine OFF, and 14~15Vdc @ 3000-4000 rpm.

Possibilities unrelated to flooding (more the opposite)---
Paint over-spray or other crud inside fuel tank causing fuel starvation at higher rpm.
Dirty or faulty petcock.
Clogged in-line fuel filer.

Good Fortune!

Nope - nothing you suggested would be an issue.

Tank is spotless inside, I haven't removed the floats and I know they're correctly installed.

There currently isn't a fuel or an air filter - both of which just arrived on order.

Voltage shows 14V with the bike running on the gauge cluster, it starts and runs great up to 5 - 6K, and then it bogs hard. No amount of feathering will get through it, and it takes a bit to recover if I do which is why I think it's flooding.

I know the issue is fuel levels in the float bowl, and I know the level isn't responding to the float adjustment. I used the clear tube on three of the four carbs and all three are too high even with the float set to have the fuel level as low as possible.

I don't want to throw $80+ at floats if it's just the needle assembly, but I also don't want to just get the float needles only to find I should have bought floats...

Hoping someone has had a similar issue, or can at least confirm that this is a known issue with plastic floats...

Rabin

bean wrote:

...starts and runs great up to 5 - 6K, and then it bogs hard. No amount of feathering will get through it, and it takes a bit to recover if I do....

Perhaps not here, but that's a classic description of performance with a clogged fuel tank cap vent.

If not already done, easily tested by attempting to duplicate the problem while running with the cap ajar (loose, not snapped down).

Has spark quality been visually observed as a healthy fat blue spark? Could be weak for whatever reason, including old hard leaking plug wires.

Just thoughts as they pop up. And not as suspicious of simultaneous carb failures from just sitting a few months and still clean inside.

Good Fortune!

Thanks! At this point I'll try anything. So after work I'll loosen the cap - see if that helps. Can't hurt anyway.

I have tested for spark and it's OK, but not a fat blue - so now I'll be wiring in the coil power mod with the relay to ensure they're getting peak power delivered to them.

It does strike me odd that the issue came up after sitting for one season, but when I couldn't adjust float levels I figured I'd found the issue.

I sure hope it's a plugged tank vent! (Something I'd never have thought of.)

Rabin

bean wrote:

I know the issue is fuel levels in the float bowl, and I know the level isn't responding to the float adjustment. I used the clear tube on three of the four carbs and all three are too high even with the float set to have the fuel level as low as possible.

Sounds like the needles can not seal against the seats. Take the needles/seats out. Check the tapered portion of the needle to make sure it is smooth and not pitted. I use a hand drill to spin them and polish the tip with 600 paper. I also spin the brass seats and polish them with a Q tip and polish. If they seal tight, they will cut off the fuel flow.

bean wrote:

it starts and runs great up to 5 - 6K, and then it bogs hard. No amount of feathering will get through it, and it takes a bit to recover if I do which is why I think it's flooding.

It could be flooding but it might be a plugged main jet. Flooding will usually make a bike VERY hard to start and it will run like crap at just about any speed.... been there, done that.

A plugged tank vent will literally make the engine run out of gas from a vapor lock in the gas line: the engine will start sputtering and lose power at just about any RPM. Also done that....

Did these carbs get cleaned after sitting for a season?

Patton wrote:

...Would verify voltage reaching coil is 12-13Vdc with engine OFF, and 14~15Vdc @ 3000-4000 rpm....

bean wrote:

Nope - nothing you suggested would be an issue...
Voltage shows 14V with the bike running on the gauge cluster....

Voltage reading on gauge cluster doesn't necessarily reflect amount of voltage actually reaching the coils, which for various reasons may be far less.

Voltage at the coils, meaning the coil primary terminals, is the critical measurement, not the voltage across the battery terminals or anywhere else.

Fuel fouling over all cylinders could result from poor spark quality due to insufficient voltage at the coils.

Carbs are often wrongly blamed for performance problems actually due to poor spark (for whatever reason) or weak compression (for whatever reason).

Good Fortune!

With the carbs mounted I removed the fuel bowl and confirmed that the float needles are indeed working and shutting the fuel off when the float is pressed up closing the needle on the seat.

What was odd is that no matter what the float tang setting, the level was high in the bowl. I was told the plastic floats are solid plastic, but they can get porous and may not float as well. Same guy figured it was likely the needle and seat needed changing. Since fuel is stopping - I figured the seat was OK and the floats were crap.

Now I'm not so sure.

Also not sure about the tank vent - I would expect vapour lock to kill the bike, but I can ride an hour at 5K in 5th.

Pilot, main, emulsion tube above the main, all the passages - everything about the carb is spotless. I've dumped so much carb clean on it I've ruined the black paint finish on much of the carbs...

I can also see spark being an issue, but I can't see it killing the bike the way this is bogging out. I've got the level down a little, and that raised the bog from 4K to the current 5500 rpm - so I'm confident the level is the issue.

Seems weird that plastic floats would fail though - thus the post here...

Rabin

bean wrote:

With the carbs mounted I removed the fuel bowl and confirmed that the float needles are indeed working and shutting the fuel off when the float is pressed up closing the needle on the seat.

What was odd is that no matter what the float tang setting, the level was high in the bowl. I was told the plastic floats are solid plastic, but they can get porous and may not float as well. Same guy figured it was likely the needle and seat needed changing. Since fuel is stopping - I figured the seat was OK and the floats were crap.

Now I'm not so sure.

Also not sure about the tank vent - I would expect vapour lock to kill the bike, but I can ride an hour at 5K in 5th.

Pilot, main, emulsion tube above the main, all the passages - everything about the carb is spotless. I've dumped so much carb clean on it I've ruined the black paint finish on much of the carbs...

I can also see spark being an issue, but I can't see it killing the bike the way this is bogging out. I've got the level down a little, and that raised the bog from 4K to the current 5500 rpm - so I'm confident the level is the issue.

Seems weird that plastic floats would fail though - thus the post here...

Rabin

...can ride an hour at 5K in 5th.... -- not at all unusual with partially clogged cap vent.


Simultaneous float valve degradation or simultaneous loss of float buoyancy in all 4 carbs over a few months storage just doesn't seem likely imo. Seems highly unlikely.

Given correct installation of floats, should be able to sufficiently lower fuel level by adjusting the tangs.

Presupposing that fuel levels were the same "too high" before and after storage, and that the clear tube test was correctly performed, and that the float valves (needle and seat) are the correct parts for these carbs ---
One conceiveable reason for failure of the tang adjustment would be that the float seat is too high for the tang to push the needle far enough into the seat regardless of maximum tang adjustment, which might result from missing 0-Rings on the seats.

Here's a pic (see below).

Now after all that, keep fingers crossed for simply a clogged cap vent.

Good Fortune!

A damaged seat 0-ring might allow fuel to escape around outside the seat and into the bowl regardless of how tightly the needle tip is seating in the seat orifice.

Maybe all that carb cleaner also did a number on the seat 0-rings. :laugh:

Good Fortune!

With the carb mounted, float bowl off, petcock on prime and the float held up in the closed position - no fuel at all is coming out.

Funtionality of the seat is working as it should as far as I can tell. Flows fine when released, and stops dead when you hold it up.

Problem has been there from the start - so I don't think the carb clean did them in...

No mention of dodgey floats though - so I'm less inclined to replace them...

Man - it's so much easier when the carbs are gummed up, you clean them, and then they work!

I'll know if it's a vent issue aftr work on the ride home.

Rabin