Bs-34 mikuni carb issues.

[stephen]

Hello all. i am having some carb issues that is frustrating me, I sent the carbs out to be remanufactured and they did a good job, But im having issues with the needle and seat, when i fill the tank im using to test the carbs the bowls fill up and sit there for about an hour then will start leaking out the front hole on the carb its 1and 3 that are leaking ive pulled the bowls off put a hose on and blew into carbs they seem to be sealing especially when i hold it down a bit but other times seems to leak a bit. I have adjusted float height , all parts are new in carb the needle is steel . ive been at it for days just when i think they aren't going to leak an hour or 2 go by and hey start leaking again, i really dont want t send them back for it takes months,, what could the issue be, sealed for an hour then start leaking, carbs are off bike didnt want fuel running into cylinders again, does anyone have an idea what it could be . clean gas and filteres are used it has me stumped why they are doing this. the bike is a 1980 gs1000g suzuki.

[Nessism]

You can't expect the needle and seat to hold back the fuel for an hour. The bike will never experience a similar situation in the real world. It could be that the needles and seat are cheap aftermarket, so they don't hold particularly long, but I'd say that as long as they hold back the fuel for 10 minutes or so, you should be okay.

[LAB3]

Sounds to me like you need to either get your vacuum petcock working properly or switch to a manual petcock and turn off the fuel when you shut the engine down. Pretty much everyone who's been around these bikes awhile will tell you the same thing.

My "theory" for lack of a better term is that a vacuum petcock is never fully "on" since the vacuum it's getting pulses as the engine intake valves open and close thus keeping the carbs from flooding while the engine is running.

[Nessism]

My "theory" for lack of a better term is that a vacuum petcock is never fully "on" since the vacuum it's getting pulses as the engine intake valves open and close thus keeping the carbs from flooding while the engine is running.

Actually, no. The engine produces more than enough vacuum to hold the petcock open while the engine is running. The engine is using fuel any time the bike is running, so there isn't time for the carbs to overflow, even if there is some seepage past the float valves.

[LAB3]

That thought popped up due to asking myself the following question: "Why would a carb NOT overflow with the engine running but WILL with the engine NOT running?"

[stephen]

Thanks for all the replies. it has never leaked before the rebuild maybe its because im just using a spare lawn mower gas tank and not the bike tank . i havent been able to get out to it last week or so.

[Suzukian]

If the vacuum petcock isn't holding, that would be a separate issue from leaving the bike on in "PRI", and it leaking. Leaking in the "Run" or "ON" position, then you have a bad vacuum petcock. You could just put an in line shut off valve, if is is leaking from the on position, but you have to remember to shut it off, as the extra gas is going into the crankcase. I would check the oil and make sure it has no gas in it

To be honest, I'd check the whole system. You can apply vacuum with your mouth on the vacuum hose to turn on the gas. Should you see the gas leak in the normal position that would indicate a leaky petcock. Rebuild, or replace. Depends on what parts you can get.

[stephen]

Thanks i got it straightened out floats were off a lot i adjusted them and seems to be ok now.