Massive fuel consumption

[Mafiera]

Hi
I have a gs750 1977
It's running rich
The fuel screws underneath have been messed with so I set them to one turn out
It was running really rich so turned them in an eighth
Bike is very responsive at lower revs a bit lumpy mid range and plenty of power top end
The guy I bought it off took carbs off and sent them to a mechanic cost him ?200 replacing all o rings gaskets and set up
I have 4 into 1 and 102.5 mains
I bought a gallon of petrol and did under 10 miles before going onto reserve
Any Ideas why I'm using so much fuel??

 

[rphillips]

The early GS750"s had like a 4.8 gal fuel tank, & appx. .9 gal on res. If the tank was empty & you put in 1 gal. you will go to res. very soon. If you put in .8 gal. it would not start unless on PRI or RES.

 

[Gorminrider]

That was the exact why and how answer!^^I would've said, fill the tank, look for drips, expect 40-50 miles per Imperial gallon which is not as good an answer. otherwise, You can't really know mpg without "normal use". It can vary for a whole lot of reasons, including the fuel level in the tank!

 

[Big T]

First, the pilot fuel screws only control idle mixture
Things to consider
Pilot air settings
Float height
Fuel cock leaking gas down the vacuum line
Needle settings
Leaking fuel junctions between carbs
Vacuum carb sync

Sounds like the "carb guy" didn't do a very good job

 

[Guest]

Do you know what size pilot screws you have? The '77s came with a variety of pilot sizes, from 15 to 27.5 - check out this post: https://www.thegsresources.com/_for...-Service-Bulletin-From-Suzuki&highlight=gs750. Depending on which size you have you'll need more/fewer turns out from seated...you'll find this out from plug chops, but getting in the right ballpark before starting will save you some time. I started with the standard recommendation of 1.5 turns out not knowing I have 27.5 pilots and it was SO rich.

Big T, not to be contrarian, but on the VMs the pilot circuit affects the entire throttle range. It's kind of the 'baseline' fuel flow onto which needle and main circuits are added. Check out page 3 of the VM tuning manual: https://drive.google.com/file/d/15DS201EFzcLm_geLgu_iOkBsiAqBvoE3/view?usp=sharing. It's unlikely this is his problem...just being pedantic

Check your plugs at various throttle openings and go from there. That's the only way to narrow it down.