Very very low MPG!

[Omran]

Hey guys,

I've been enjoying my Vmax for the past 5 months until the gearbox broke down and I had to park it for a while until I got it fixed.

Now my problem is, and this has been going on since I bought it, it runs a very low mile per gallon, and by low I mean from full tank to fuel light coming up in less than 50 miles.

From what I read online it should have a good 150 miles per full tank. First I tried playing around with the carbs, didn't get me anywhere. Changed the spark plugs, cleaned the carb, air filter, checked for leakage in the fuel tank, and still nothing has proved to be the source of the problem.

Iunno if it might be the needles are stuck or if I need to take apart the carbs and see where that leads me, but I figured I'd post to the forum before taking any other steps.

So what do you guys think could be the problem?

I'm also thinking of removing the filters from the exhaust for a louder noise and better speed, if so do I need to jet it afterwards?

Oh, and one last thing, the little switch that sits beneath the clutch lever seems to be dead, so I removed it, found little metal parts inside that were scrambled all over the switch's insides. I'm trying to put it back together but I don't know how the mechanism works, so if anyone can post me a photo from the insides of the switch of an illustration of how it works I'd be very grateful!

Thanks and I hope I'm not asking too much questions :whistlin:

 

[tugla]

100 miles for sure and it seems to very after that... for sure a good carb cleaning there are lots of threads that show you how and what to do....dont cheap out and make sure you get yami parts not jobber ones to put back in there such as gaskets.
then a dry float setting along with wet and carb sync to set everything to a good base line.

check the tank for rust, clean or chg if needed, chg fuel filter and even add another one after the fuel pump for safe measure......
id start there and see how it goes.

oh if you are into the vboost as you should be while driving, if your in that lots then for sure the mileage will be low......

 

[mr.maxx]

is the bike stock? any carb jetting changes or a stage 7 kit maybe? all of which will affect fuel mileage.

 

[Rusty McNeil]

50 miles to a tank is so low that your getting into "ring wash" territory.

That's where it's so rich the unburnt fuel rinses the oil off the cylinders and the rings lose seal, followed by excessive oil consumption and lowered compression.

I wouldn't ride it like this very long.

 

[naughtyG]

The only time I ever saw this kind of consumption my needle valves weren't sealing (because of rust dust from the tank) and petrol was constantly leaking through to the point I was getting fuel puddles under the bike through the exhaust joints!

Does your bike smell of fuel a lot? How does it run?

 

[Omran]

It runs a bit rough, I smell raw petrol all the time, and I haven't modified anything in the bike, it's all stock!

 

[davesax36]

50 miles to a tank is so low that your getting into "ring wash" territory.

That's where it's so rich the unburnt fuel rinses the oil off the cylinders and the rings lose seal, followed by excessive oil consumption and lowered compression.

I wouldn't ride it like this very long.

Is top end work the only way to cure this? Is it possible for the bike to run smoothly and still be in this state (ring washing)? My bike seemed to be under-powered when I got terrible mileage like that. I have to fix a clutch issue before I test it again,but my sync was WAY off. I have strong gas smell now, but I'm hoping that's idle richness. There doesn't seem to be fuel in my oil or thick smoke. I'm pulling the motor next month anyway for transmission work. If I'm destroying things by riding, I might just have to look for a whole new motor.

Sent from my Galaxy Nexus using Tapatalk 2

 

[Rusty McNeil]

Is top end work the only way to cure this? Is it possible for the bike to run smoothly and still be in this state (ring washing)? My bike seemed to be under-powered when I got terrible mileage like that. I have to fix a clutch issue before I test it again,but my sync was WAY off. I have strong gas smell now, but I'm hoping that's idle richness. There doesn't seem to be fuel in my oil or thick smoke. I'm pulling the motor next month anyway for transmission work. If I'm destroying things by riding, I might just have to look for a whole new motor.

Sent from my Galaxy Nexus using Tapatalk 2

I wouldn't assume you have any ring problems just yet, just wouldn't ride it a lot this way.
I'm just paranoid about this one, never realized the damage that could result until improperly tuning my wife's supercharged Nissan and going so rich it did that. And yeah once the damage is done a ring job at minimum is required to fix it.
You have to be really, really rich to make that happen in a hurry, like black clouds of smoke out the tail pipe rich. No fuel smell in the oil is a good sign.
The other way it can happen is by cranking a heavily flooded engine way to long getting it started, this can happen on brand new engines on initial start up if someone is overly persistant in trying to fire up a new engine thats getting fuel but not firing the first time.

I wouldn't worry about it if I were you, just get the carbs sorted and then go from there.

"Don't borrow trouble" as my grandma use to say....

A compression and leak down test should tell you what condition it's in if you want to go to the trouble, but if its rich enough to get that kind of mileage the reduced power could be from too rich an a/f mix I'm guessing, since you've already proven your fuel consumption is through the roof.
If you're pulling the motor anyway I would definitely do a compression test first to help decide if it could use new rings and or pistons or a valve job before pulling it without regards to this issue, just as general good practice.

If you decide to search for info on "ring wash" don't get too confused by the terminolgy...Some times it's referred to as "fuel wash", but to make it even more confusing "fuel wash" has a totally different meaning on two strokes and is a diagnostic tool used by reading the "fuel wash" i.e. the color distributuion across the tops of the pistons on two stroke motors....sort of similiar to reading spark plugs......