GS750 frustrating carb leak

[Hubba]

Hi all! First post, so be gentle..

I'm at my wits end with this problem. The carbs are leaking heavily out of the float bowl overflow tubes. Doesn't matter which carb, it picks them at random. When I tap on the bowls it doesn't stop. Which doesn't make me think it's not sticking floats?

So far I've done the following,
Changed the float needles and seats
Cleaned thoroughly and made sure the floats clear everything
Cleared jets

It continues to flow after the engine is switched off for about 5 seconds. Which perhaps suggests petcock but it does it when the bike is on or off and doesn't leak when it's sat on the side stand. I've ordered a petcock rebuild kit but will this solve it or make things worse by breaking it down?

Any help appreciated!

[chuck hahn]

Check the actual float HTS. If its a 77 or 78 you should see right at 24MM. Take the gaskets off the bodies and measure from then raised bead to the top of the floats as they gently rest on the float needles themselves. Check the spring loaded plunger on the float needles as well to see they are free.

Service manuals here and carb rebuild tutorials along the right side margin.

http://members.dslextreme.com/users/bikecliff/

[chuck hahn]

Rebuild kits are maybe a 25 to 30 % success rate of ever working. They tend to come with the wrong size oring and dont seat..or fail within a week or so.

[Nessism]

Instead of checking float height try using the clear tube method to measure fuel height in the float bowl. This test is detailed in your factory Suzuki service manual. Also, check to see if the petcock works properly. Pull off the fuel line and vacuum lines and install dummy lines and then test. Make sure fuel doesn't back flow down the vacuum line as well.

[Hubba]

Cheers for the quick replies chaps! Float heights are all set at 26mm as per the haynes... Ill drop it to 24mm and see how I get on. I will also give the clear tube method a go.

As for the fuel tap I'll test it. Just to check, if I put a tube on the vac line then another on the carb feed into a can, then suck on the vac line with it on and on reserve this should be the test?

Cheers!

[chuck hahn]

I stand corrected. Instead of going by memory, I checked the 8 valve manual on Bikecliffs website. Page18..Float hts 25 to 27MM. So if your at 26 now and they are getting too full and overflowing, I would be sure the floats are indeed shutting off fuel flow, the gaskets arent hanging up on the floats ( its been known to happen ), and use the tube to see where the fuel level is in each bowl. Page 18 also shows the test tube and gives the range your looking for. Do this off the bike with the carbs level so you dont end up taking carbs on and off several times to make adjustments.


Check the overflow tubes to see they arent cracked too.

http://zeus.mtsac.edu/~cliff/storage/gs/GS750_Service_Manual_early8valve.pdf

[Rensdw]

Check fuel tank, I had the same issue, turned out it was small pieces of rust in the needle seat, after cleaning the rusting tank would just make it leak again.