Cafe Racer Forum banner
1 - 20 of 33 Posts

·
Registered
1977 Suzuki GS750
Joined
·
11 Posts
Discussion Starter · #1 ·
My bike leaks gas out the over flow lines while the bike is running and goes through my gas pretty quickly. I have put all the pieces of beside the needle of a carb kit in all four carbs to fix the problem. It still leaks gas out of the same carb which is the left middle and sometimes it’s will leak out the right middle one too, any thoughts
Fuel tank Tire Land vehicle Wheel Plant

Tire Automotive tire Automotive lighting Tread Vehicle
 

·
Registered
Joined
·
2,737 Posts
Float valve seals are bad or floats need to be adjusted. I don't remember if these carbs have seals on the float valve seat, but that may be worth checking for as well.

I'll add (im assuming you already know this) that you should absolutely not ride the bike until this is solved due to the obvious fire hazard
 

·
Registered
Joined
·
7,627 Posts
Works the same way as the mechanism on the back of your toilet. Float needle and seat needs to seal the valve shut or motorcycle fuel Incontinence will result.
It must also be performing very poorly.
 

·
Registered
Joined
·
7,627 Posts
IF your carburetors have floats that are plastic or metal, something that can easy be over-looked is that hollow floats can become 'waterlogged' if fuel gets inside them they don't float any more so the fix can be to repair the float so it does not leak any more. :geek:
 

·
Registered
Joined
·
7,627 Posts
What you need is a mentor. Somebody familiar with motorcycle carbs and willing to teach you. I don't think it is possible to own an old motorcycle with carburetors and not know how to service them. It would cost too much.
it's also not difficult once you understand what all the individual parts do.
 

·
Registered
1977 Suzuki GS750
Joined
·
11 Posts
Discussion Starter · #9 ·
@TrialsRider yeah I don’t really want to pour to much money into this. I’m gonna try and find some to look at it but should I just go ahead and get new floats since they are probably the original ones
 

·
Registered
Joined
·
7,627 Posts
@TrialsRider yeah I don’t really want to pour to much money into this. I’m gonna try and find some to look at it but should I just go ahead and get new floats since they are probably the original ones
No. Do not buy anything until you test and inspect what you have, the original parts are by far the best parts to work with.
Any old guys ride motorcycles near where you live? any racing motorcycles?
I went to a night school class on motorcycle mechanics about half a century ago, those are good if they exist near you.

Likely best and easiest first step is a service manual, and those exist both for your motorcycle and for the carburetors (y)
 

·
Registered
1977 Suzuki GS750
Joined
·
11 Posts
Discussion Starter · #11 ·
@TrialsRider i don’t really know anyone that can besides taking it to this shop that’s close to my house

Also I have the original service manual but it doesn’t give much on tuning it sadly, I may try to get a Haynes manual for it. Also do you have a link to a manual for the carbs?
 

·
Registered
Joined
·
2,737 Posts
You should be able to find a diagram using Google. The GS forums should also be able to point you in the right direction. But that being said, these carbs are pretty similar to most of the era.

Worst case, I have a set of junk 79 GS750E carbs that I can pull apart and check to see what seals you'd need.
 

·
Administrator
Joined
·
27 Posts
@CaTacL1sm I’ve already replaced the float valve seals and all the floats looked to be at the same hight
This is not good enough. They must be measured properly. Does it still have the factory vacuum activated petcock? These commonly go bad at this age. Rebuild kits for these rarely work. Best fix is an OEM petcock. But first check the float heights by measuring them. Can't be eyeballed...
 

·
Registered
Joined
·
2,737 Posts
Did the 750s have a vacuum petcock? I know they had some sort of vacuum system. The previous owner of mine blocked the ports off on both the valve cover and carbs and a gravity petcock.

I'd bet however that your floats are the primary culprit. Check them on the bike with a hose or on the bench with calipers. OR there's some crap in the carb fuel rail/connectors thats getting stuck and keeping the needle from closing... personal experience with that
 

·
Registered
1977 Suzuki GS750
Joined
·
11 Posts
Discussion Starter · #15 ·
@CaTacL1sm @Spyder13
It has the original petcock to the bike and works fine, it took a look at it and it’s oddly good for it’s age

I will check the fuel rails and all the floats heights

I think now It’s either the floats are bad or gas is getting blocked
 

·
Registered
Joined
·
7,627 Posts
Super easy to test, With the fuel tap off, remove the 4 JIS star screws holding the float bowl, lift the little float half way up with your finger, turn on the fuel petcock and if you can't stop the flow of fuel by raising the float slightly you confirmed a problem. If you can stop the fuel flow at the same place on all the carbs (y) if you find a float that is heavier then the rest, you found another problem.
 

·
Registered
Joined
·
7,627 Posts
If it has a vacuum petcock fuel should only flow when there is vacuum applied to the fuel tap and that comes somewhere off an intake manifold. or you suck on the vacuum hose, that works too.
 

·
Registered
Joined
·
7,627 Posts
If it's a Keihin carb : Carburetor Tuning | Keihin North America is a good resource
if it's a mikuni carb there will be an equally good or better resource for their carbs too.

Good news is you have one of the more simple carburetors by design, bad news is you have 4 of them and they all need to work perfect.
... another little hint of carburetor float level being off slightly; the bike works better with the front end elevated, or on a steep decline angle. That tilts the carbs and makes the off level problem more pronounced in one direction or the other :geek: for example: the bike stalled out every time the front wheel is tilted down a steep slope. <- float level is off.
 
1 - 20 of 33 Posts
Top