Need info on my differential

[Scaryfast]

I would like to improve my fuel economy on my VMAX. On long rides I'm only getting 90 miles on a tank. I was thinking I could rebuild my diff with venture parts fairly cheaply to lower my highway rps. What would the fuel savings actually be, and would i be money ahead just replacing the whole pumpkin instead of rebuilding. I would like about 120miles on a tank if possible. I found a replacement fuel-tank for my max but holy crap they want $900! I also wouldn't mind the higher speed unk:! by the way mine is a 97.

 

[maleko89]

What's your current jetting setup? You should be getting at least 130 miles to a tank with a stock 1200.

 

[4gasem]

Yeah I can do 120+ on mine with Sean Morley's kit installed depending on conditions...

The disadvantage of the Venture pumpkin is reduced acceleration. If that's not an issue then go for it!

Chris

 

[naughtyG]

I use a Venture pumpkin. The difference is 500 rpm lower across the range. Here's how it goes:
3000 = 55
3500 = 65
4000 = 75
4500 = 85
5000 = 95 etc

My '86 also only does about 90 miles from full to reserve under normal riding conditions, and regularly return 105 miles b4 the red light comes on when riding highway only (@ 85 mph).

I've NEVER seen more than 107 miles before the reserve light. I believe my carbs are good, my sync is spot on, plugs look good, and the bike is totally stock other than the K&N air filter.
OTOH, I weigh in at about 220 all geared up and with my laptop, I have a big windshield and the Fatmax hard bags, so maybe these all contribute a bit, at least on the highway.

Other than that I'm coming up to 45,000 miles so I'm thinking a valve adjustment is due, when I get round to it I'll see if fuel economy improves.

About the Venture pumpkin though, I like the reduced rpm on the highway, and didn't notice much difference on acceleration, but in terms of fuel economy I felt it made just about zero change. I think Sean's overdrive (-1500rpm) could be a better choice for long trips, but I can't afford that now.

 

[one2dmax]

Ive got a few diffs left but if the economy of 120 is what you are striving for you can get that with stock carbs (with almost any kit except maybe the stage 1's). Check the float levels, main jet selection, and needle settings. Probably too rich.

Sean

 

[naughtyG]

Ive got a few diffs left but if the economy of 120 is what you are striving for you can get that with stock carbs (with almost any kit except maybe the stage 1's). Check the float levels, main jet selection, and needle settings. Probably too rich.

Sean

I set my floats dry on the bench using the casting mark. Main jets are stock (152.5) and needles are stock as well (they used to be shimmed but I took that off).

Do you think valves could be the culprits for my poor fuel economy, or just engine wear and weight combined?

I wonder what mpg Bill gets with his 120k miles..

 

[4gasem]

That huge wind screen and bags don't help.

 

[naughtyG]

That huge wind screen and bags don't help.

Yea I'm thinking that too.. I might ride a whole tank without them just to see.

Not gonna happen for a while though, I'm off on tour in Europe on Saturday, and won't be back 'til early July.

Last ride for a while tomorrow - I'm gonna enjoy that! :eusa_dance:

 

[one2dmax]

Yes, the screen will kill more then you think. Check the levels wet and see. We've had one carb that was perfect when dry but off when wet. Each time would vary. Ended up the stud holding the float was too long and flexing when bolting the bowl on.

Sean

 

[maleko89]

Yes, the screen will kill more then you think. Check the levels wet and see. We've had one carb that was perfect when dry but off when wet. Each time would vary. Ended up the stud holding the float was too long and flexing when bolting the bowl on.

Sean

Wow, weird. From now on I think I'll measure those with my caliper to make sure.

 

[Scaryfast]

Ok, Looks like I need to have those carbs looked at. I have no idea how to set and sink them so I guess ill have a dealer do it for me. This bike has always ran great since i bought it. But it may be a bit on the rich side, I do smell a bit of gas when Idling. Will leaning it out effect the way it performs? If so maybe i should just get a bigger tank.

:ummm:

 

[naughtyG]

Check the levels wet and see.

Sean

Just remind me, to check them wet, I need to..?

 

[06VMAXIMUS]

My bike is bone stock, with saddlebags and full fairing...I get 120-130 miles before the reserve light comes on...smells a little rich at idle, but plugs look light tan. I suppose it matters what mods you have, how large you are around the waist, and how hard you twist the right hand that can really effect fuel consumption!

 

[one2dmax]

there should be a sticky on here that shows the wet check.

Sean