Float bowl overflow on '81 KZ 750 ? !

Hello, looking for help with a problem that began with installing a Dynojet kit on my son's '81 Kz 750 E. After insalling the stage 3 portion , with Emgo pods and a Vance & Hines 4 into 1 the #4 carb leaked from the overflow tube on the float bowl. Thinking that perhaps the float tang was inadvertently bent he adjusted it for less height. Presto! The leak was gone , only to reappear on the previously fuel tight #1 carb. Is something we have done pressurizing the floats? We're missing something and any help would be greatly appreciated.

It is a long shot but maybe the #4 was pulling enough fuel that #1 never had enough to overflow? Does the #1 flow seem slower than the original one?

Have you done the clear-tube test to see where the fuel level is in the bowls?

The usual reason for overflow is a tiny microscopic speck of dirt under the float needle valve. In taking the carbs off to replace the jets you may have disturbed some crud in the fuel line or the bottom of the gas tank. If you dont have a filter in the fuel line you should get one. To remove the dirt without removing the carbs you can sometimes open the drain screws and turn the petcock to prime and see if you can flush . Otherwise take the carbs off, remove the bowls, remove the floats and the float valves and run a Q tip around the brass float valve seat.

Good luck

Thank-you for the suggestions. This is all so puzzling because there has never been a float height issue on this bike before. So here I will admit to never having properly set float height with the clear tube. I guess this lends credence to the impurity theory. The part that got me thinking about pressure is that Dyno Jet tells us to remove the vent tubes. It seems that with no tubes that a low pressure area could exsist under the float bowls drawing more fuel into them and then out the now tubeless overflow holes. If I am guilty of overthinking here , corrective measures are welcome. At any rate I will continue to try to solve the issue and post results in hope that it helps someone with a similar problem. Thanks again for taking time to help .

I'm assuming your carbs are the stock Keihin CV34s (like on my 1980 750/4) .....in which case removing the overflow tubes from the nipples on the bottom of the carbs will not hsve any effect other than allowing overflow gas to drip on the engine cases. There are other types of carbs which have vent tubes exiting the carbs higher up the carb body which are additional to the bottom of the bowl overflow nipples/tubes. Perhaps the dynojet instructions are a bit "generic".

Does the leak occur during running or when the engine is turned off? If it is leaking while the engine is off you could have a malfunctioning vacuum petcock, this is very common, and often misdiagnosed as incorrect float level or improper sealing of the float valves.

You can check this by disconnecting the fuel supply hose to the carb, in the "ON" and "RES" position there should be no fuel flowing when the engine is off (no vacuum signal to the petcock). If fuel flows when the engine is off, you will need to replace the vacuum diaphram in the petcock.

I have also had leaky float bowl over flows, the brass tubes crack with age and abuse, and then they drip.

mjg15 wrote:
I have also had leaky float bowl over flows, the brass tubes crack with age and abuse, and then they drip.

A lot of people fight with an over flow problem and never figure it out. Glad you brought this up. Kind of a rare thing but will drive a person nutty! :S