High fuel consumption

78jotadave

78jotadave

Hero member
Location
Palm Desert, California. (near Palm Springs)
On a recent 1300 mile trip my bike a 78 JOTA was sucking up the fuel averaging 29-33 MPG (US gallon) :o . The engine is in top condition runs 4C cams and original good condition Dellortoes with clean K+N Pod filters (used them for years). A similar trip a few years back returned approx 37-40 mpg. The bike has excellent throttle responce, started up immediatley with just a touch of choke when cold and required no choke at all when warm. I was thinking maybe the chokes were hanging up but wouldn't it run rough ?  Carbs are in good condition. What should I look at first?
 
Hey Dave,
Just did the numbers and that works out at 13km/litre based on 32mile/us gallon. My 1200 used to return about 11km/ltr riding at speed. !200s are renown for shit fuel comsumption.
The Mikunis now give me 18km/ltr at highway speed with a much hotter motor at over 100rwbhp
 
Have a quick look at your plugs, there not as good an indication as in years ago but worth a look. Stick your finger up the mufflers as well, look for soot.
 
Replace needle jets and needles, irrespective of mileage.  These parts wear at alarming rates, not to mention the corrosion that sets in if the bike isn't used for a longer period.  Also check for wear in the carb linkage, apply a drop of oil if still OK, the bushes will be thankfull!

While improving mid-range response, I did not notice any improvement on consumption after fitting Mikunis to my triple.  Any engine in a given state of tune has its specific fuel requirements, it's just a matter of how well it is metered that determines overall consumption.

piet
 
If your chokes are in any way hanging it will from my experience give very noticeable effect on the running. Piet?s advice is what I would go with, needle jets wear gradually and don't give noticeable difference in running - until you replace them. I also don't have good experience with the oiled mesh K&N, even cleaned and re-oiled I don't think you get them clear as when they are new, I have gone over to foam UniFilter.
I remember from when Jotas were new that people said they got much better economy at 120/130kmh or so than at 100.
It looked like a fantastic trip Dave. I drove down the coast SF to LA some years ago, magnificent part of the world.
 
I guess fuel consumption improves once you get above the squirt from the accelerator pumps.
I have seen mpg (UK) improve by up to 10mpg after replacing Dellortos with Mikuni RS36 carbs.
 
That would be about half throttle Grant? Maybe a bit illegally quick cruising on a Jota in most countries.
My SF improved by 10mpg when I removed the pump levers, the only difference I could detect.
 
Hi Dave

Is all the brass in your carbs unworn?  If you mixture is out (rich or lean) the motor will run less efficiently and be gobbling up fuel to provide the power you request via the twist grip.

Illustration - I played with the throttle slide cutaways on my Jota and [before I got it fully dialed in] I caused the bike to fall to a 100 mile tankful, rather than the previous 130+. Only very small variations in general running could be detected by the arse-o-meter, yet the mpg was ruined.

Paul
 
FIRST
buy three gasket sets and a new set of choke plungers from a scooter shop (don't even look first just buy them as ethanol, age and static pressure degrades the rubber tip.)

Second
remove and strip the carbs, clean, check and adjust everything and be sure that you have K1 needles, and no silly main jets e.g. 240 (!!!) I saw a Jota last year with K14 needles, which was correct for 1200's, but normally very quickly swapped for K1's which did a lot to "dry out" the consumption of the bigger engine bikes.

Third
re-fit carbs and balance using the best kit you can lay your hands on (why do home mechanics think that rods, eyes and ears are good enough?)

CLEM
 
Pump your tyres up? Wear skin tight leathers, ditch the passenger. Then maybe do all that buggering around with carbs which i doubt will make much difference . Improve riding style. 😉
 
Thanks for all the great replies. Rob, Mikunis are a big outlay of cash which I could use to fill up the Jota tank many times with Premium which right now is cheaper than it was 10 years ago. Clem, the carbs were  rebuilt leas than 1000 miles ago, all but the chokes so yes I will be replacing them now, I have a good set of vacuum gauges so everything is in synch and linkages are always with a drop of oil. I ditched the pumpers more than 30 years ago it made no difference in performance and the bike ran cleaner especially around town.

Yep a finger up the exhaust pipe revealed a black somewhat greasy finger tip (not dry soot) but it was identical to the same test on my mates 2010 BMW R1150R. PB yeah I may try to refit the original(modified) airbox or go with foam filters.

In California all grades of fuel contain ethano no no nol (shit) made from corn around 10-12% the ethanol content is higher in summer than winter. A few states, Montana is one you can get fuel without ethanol but ethanol content is pretty much the norm in every state.
I think that explains the black greasy finger. Why we subsidize farmers to grow corn for fuel when petrol is cheap as chips is beyond reason.

Thanks for the replies guys, this site works (goodjob) Choke tips and filters it is, Cheers Dave


 
motoddrob said:
Hey Dave,
Just did the numbers and that works out at 13km/litre based on 32mile/us gallon. My 1200 used to return about 11km/ltr riding at speed. !200s are renown for shit fuel comsumption.
The Mikunis now give me 18km/ltr at highway speed with a much hotter motor at over 100rwbhp
Click to expand...

Mine runs 13kms/ltr (fast road use), has done for the last forty-four years. Drops to about 9kms/ltr (track use).
 
78jotadave said:
On a recent 1300 mile trip my bike a 78 JOTA was sucking up the fuel averaging 29-33 MPG (US gallon) :o .What should I look at first?
Click to expand...

If you had a smile on your face don't worry about it! I swapped a couple of Zanes for a RGS and that did 25 mpg until Maurice looked at it! Well he didn't look at it he could smell it whilst he was riding behind me.
 
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