Fuel Consumption

[Dixie]

Hi All, me again with yet another question.  What is the expected fuel economy on a 79 GS750. I reckon out of a full tank I'm getting around 100 miles and that's not ragging it, I reckon pretty average riding. At 3.5 imperial gallons that's under 30 mpg. I have read that I should be getting around 40 mpg.  

I'm wondering if the carbs want overhauling.

[johnr]

have you checked the plug colour?

[gs7_11]

Yep, that's wrong. Should get mid to low 40s easily.

[CockneyRick]

if you're worrying about consumption, you'll get lighter as you waste away. Problem solved  

[Dixie]

I'll have a look at the plugs at the weekend, I'm wondering as its an ex Dutch bike would the carbs be set different for a different octane of fuel. Yep as I said, I'm sure I read somewhere I should be getting over 40 to the gallon.

 

[johnr]

fuel consumption is a subjective thing. rg owners would take the chance of 30mpg readily. so before fretting about its consumption, you need to first check how its burning, and then make sure its not losing fueel either from a leaky tank or pipe, overflowing carb or through the cabs down the bores. next job would be to check what your jetting is, make sure your air filter/s arent clogged or your exhaust is clogged or restricted. finally, you need to mak sure that someone isnt nicking your fuel when you park up (seriously, i once had an x5 that was only doing 30mpg till i realised the local scrotes were pulling the petrol pipe every few days from the tap and draining juice out for their little shit peds)

[Dixie]

Hi Johnr, right I've checked plugs, all sooted.  Oil doesn't smell of fuel so I don't think there is any dumping, the fuel tank isn't leaking neither are the pipes, the bike is locked away in my garage when not in use so no theft issues and the air filter is brand new.  Before I remove the carbs what notch should the needles be set on as standard?

[gs7_11]

If all 4 plugs are the same, logic says start with something that will affect all 4 cylinders, since its less likely that all 4 carbs would have the same fault, although not impossible.

What about the air filter and airbox? Any issues with that? Is the filter itself clean, and importantly NOT over oiled?

Then there are things which could be off on all 4 carbs, like has someone set the air or pilot fuel screws incorrectly, but the same on all 4? Have the float heights been set incorrectly on all 4? Needles come under this heading, but are less of an issue as the adjustment available is not that dramatic.

Finally, you might have the same fault on all 4 carbs, such as leaky float valves or leaky o-rings at the float valves or chokes for instance. These bikes are of an age now where you can't assume anything is working correctly, and even a low mileage bike might need a carb overhaul with a complete new set of o-rings.

 

[Dixie]

Nice one, I reckon a carb overhaul wouldn't hurt, as I mentioned the air fuel is brand new, I'll order a kit for each carb. It fires up without any hassle, runs well and picks up pulls really well but still feels like it's hunting at steady throttle, is that normal? 

[gs7_11]

No, carburation should be spot on.

Sound like a good overhaul would be the place to start. I like Keyster carb kits, and you can get a set of o rings from cycleorings.com

[Dixie]

Spot on I'll get a kit ordered, thanks for the info