Gas leaking from overflow

So, I just bought this 1979 KZ750 twin bobber yesterday. I rode it home on an hour long trip. No problems.

This morning I went and got plates and registration all taken care of.

I came back this afternoon and went out to put the plates on and noticed gas leaking from the area circle in the picture. Left side carb.



I sent to the picture to the guy who bobbed the bike for me. He sad that the area was the float overflow and that I should try running the bike for a few minutes and then tapping on the float casing with a hammer to see if the float will loosen up.

I did this then I let it sit for a while. 2 hours later I checked on it and it is still leaking so I run it and tap on it some more and the bike sputtered and died while idling. Got the bike running again by using slight throttle, tapped on the opposite side carb, and the idle steadied and the bike kept running.

I still have gas leaking. I know very little about carbs. Any and all help would be greatly appreciated.

Should there be a hose attached here?

Turn OFF the petcock when the engine is not running. Check the fuel tap to see if fuel is getting by when off.

i have already been turning the petcock off while not riding. should have mentioned that in the first post. still leaking. i know i will probably have to have the petcock replaced, but i am more wondering about the overflow since i know so little about carbs in the first place.

AjKZBobber wrote: i have already been turning the petcock off while not riding. should have mentioned that in the first post. still leaking.

That means the petcock is hosed, I already replaced mine once on my 750 twin. They are no longer available.

You can fix the leak by:

1) Checking/adjusting fuel levels in bowl.

2) Clean (replace as needed) the inlet needles and seats. That is the NUMBER ONE cause of fuel overflow leakage.

Yes, there should be a hose attached but that won't help stop the leaking.

Just an educated guess but most times when it over flows the petcock will leak in the OFF position. The float needle in theriory should stop the flow but when it gets past the needle seat it will overflow and in many cases will flow into the crancase and contaminate the engine oil, do you smell fuel in your oil, is the oil level way high? You should run overflow tubes from the nipples to the ground so your motor does not have to get soaked from the fuel that is leaking. Unhook the hose from the petcock to the carbs and see if fuel is seeping from the petcock when in the off position

The real problem is: gravity always wins. You have an imperfect mechanical valve (petcock) in series with an imperfect mechanical valve which is the inlet needle/seat, but the gravity will make the gas seep downwards. If both valves are good, the seepage is so low that evaporation in the bowl is enough to keep it from overflow flooding. But if the petcock is not sealing well (old ones never do) then the carb valves are critical.

I used to do routine maintenance: drop the bowls and remove the floats, then remove the needles and brass seats. I chuck the needles in a hand drill and polish the tapered tips with 600 paper/oil until they are mirror smooth.

I chuck the brass seats and polish the inside area where the tapered tip meets witha Q Tip and chrome polish until it is dead smooth.

Set the fuel levels to be 5 - 5.5mm down from the lower edge of the carb upper part.


NOTE: taking carbs apart, label floats, needles and seats and dont reverse them.

Protect needles and seats with tape in the drill when you spin them.

I will probably just have to take it to a garage to have it fixed. I live in a condo building and, therefore, i have nowhere to work on the bike myself. I don't think that they would like gas pouring on the ground either.

Go the cheap route and buy an inline shut off valve and install it in the hose between the petcock and the carbs.

Goto any parts store and get one. $5-10. Then you still should check out the float valve later.

Flyndrive wrote: Go the cheap route and buy an inline shut off valve and install it in the hose between the petcock and the carbs.

Thanks for the suggestion. Sounds like a good idea.

AjKZBobber wrote:

Flyndrive wrote: Go the cheap route and buy an inline shut off valve and install it in the hose between the petcock and the carbs.

Thanks for the suggestion. Sounds like a good idea.

Problem is stuffing a valve in there. On the 750 twins, I barely found room for an inline filter. Couldn't fit a shot off valve, but maybe there's a way I just don't know about.

Have you tried taking the hose off the carbs and watch for a leak straight from the petcock ?

I'm having some trouble with my new needles and seats, a couple of carbs are over flowing and will continue to drip after the bike is shut down but I believe it is due to the fuel left in the lines, once they are empty , no more leak.

My bike has a vacuum petcock and I know it is working right.

I just got one of those fuel level gauge tools from Z1E
www.z1enterprises.com/SearchResult.aspx?...e&KeyWords=ZSM01-208

Should be squared away by sometime tomorrow , hopefully. :dry:

JD