Very very annoying problem with my KZ750

If the mixture is lean, the RPs tend to go up with heat, not down. You were correct with your original estimation that it would go down with heat if rich.

However, since you say the plugs looked lean, there may be another problem besides jetting. It may be possible your petcock stops flowing when hot, or the tank vent is clogged, or if it's like my bikes, when I use paper inline filters, the bike eventually stalls out in hot weather.

The problem for me was gone when I switched to scintered bronze filters and metal screen filters (on different bikes).

the tank vent is clogged,

That would be a nice guess if i have a vent on my tank... is it the unconnected hose barb i have on my tank with the big plastic under (it's on the side of my fuel sensor)????

It is not mentioned in the kawa manual. Never knew what that hose barb was for!

It may be possible your petcock stops flowing when hot, or the tank vent is clogged, or if it's like my bikes, when I use paper inline filters, the bike eventually stalls out in hot weather.

I have no inline filter yet... i need to find a source from a local store where i am now.

If the mixture is lean, the RPs tend to go up with heat, not down.

Yeah but you are half right ... if the mixture is way too lean to be ignited the rpm will drop significantly!
Thats what i'm seeing in the chambers ... pale blue flame and misfire once every 2-3 explosions (without backfire or pop maybe exhaust pipe are not enough hot to cause afterburn in da pipes!).

Oh yeah and there is one thing i forgot to check/clean when i took off the carb rack are the bowls vent barbs at the top.

I completly forgotten what they was for and somebody mentioned in another topic that they are for venting the bowls...

if they are clog and temperature rise (long stop??) in the carb vapor lock will happen.


Please give me again any useful tips/clue where to check next!

I will found it eventually after checking everything you say guys

ELCouz wrote:

the tank vent is clogged,

That would be a nice guess if i have a vent on my tank... is it the unconnected hose barb i have on my tank with the big plastic under (it's on the side of my fuel sensor)????

It is not mentioned in the kawa manual. Never knew what that hose barb was for!

It may be possible your petcock stops flowing when hot, or the tank vent is clogged, or if it's like my bikes, when I use paper inline filters, the bike eventually stalls out in hot weather.

I have no inline filter yet... i need to find a source from a local store where i am now.

If the mixture is lean, the RPs tend to go up with heat, not down.

Yeah but you are half right ... if the mixture is way too lean to be ignited the rpm will drop significantly!
Thats what i'm seeing in the chambers ... pale blue flame and misfire once every 2-3 explosions (without backfire or pop maybe exhaust pipe are not enough hot to cause afterburn in da pipes!).

Yes, but if the mixture was lean due to jetting, it would have stalled out while cold, before getting hot.

If it was the jets it would have started lean. Since it runs ok cold, there has to be something making it go lean as it warms up. That is usually starvation from something other than jetting.

The vent is usually in the gas cap. Easy test isto open the cap and see if it gets better. If not then it's not the cap vent that's the problem.

The vent is usually in the gas cap.

I will open the gas cap when the problem is occurring to see if it make a difference.

For sake of curiosity do anyone knows what that magical unplugged plastic hose barb do on my tank ? Early evaporative control thing maybe ?

thanks for your replies guys!

laurent

The thing under the sensor.

it's a gpz 85 tank but it's nearly the same... is that hose barb important or i can leave it unconnected???

I think my cap is sealed tight... when it's very hot outside i clearly hear a hissing sound coming from the cap. If i open it the gas pressure will go away. Something is wrong doctor ?


regards,
laurent

My gpz550 has that too. I think it was to route any gas leak at the fuel sensor. But I'm pretty sure it was never hooked up from the factory. I think they decided it wasn't needed because the fuel level senders almost never leak.

It's not a vent. It just drains whatever collects in that plastic cover, to prevent gas from leaking directly onto the motor. (That is, if there was actually a hose attached.)

thanks loudhvx for the clarification !


regarding any intake air leaks i'm gonna buy tomorrow some Permatex Moto Seal Ultimate Gasket Maker and put a little inside the carb mouth and on the intake flange. If there's any air leaks i should be good with that!

Avoid Permatex Aviation Form-A-Gasket #3 Sealant... that resine stuff got sucked by the vacuum (become liquid with heat), back to the carb by the reversion and gummed everything in the carb including the bowls ... what a mess!


regards,
laurent