Bad MPG. What jets should I get?

[jdmben]

Ive had my Max for a couple years now and have never done a tune up or replaced any parts other than an oil change. All I know about the bike is that it has Supertrapp mufflers(stock intake filter). I know the previous owner had the carbs taken apart and "rebuilt" by him. I dont know if he reused the stock jets or went bigger. So I had planned on just buying the best setup for better mpg's.

I only ride the bike to and from work cruising at around 80-85 mph. At this constant speed Im averaging around 30-32 mpg a tank. Highest ever was a 34. I punch it here and there but rarely. And Ive never red lined the bike or even close for that matter.

I realize this is a hot rod and not some econo bike. Im not looking for miracles but surely something is wrong or out of whack with this kind of mileage.

Is there a "best" jet kit for "best" gas mileage? And I plan on replacing the air filter, fuel filter and plugs but is there some other part that I should look into as well?

Any advise would be appreciated. Thanks in advance.

 

[44boyd]

sorry but those MPGs is pretty good. Only way to get better would be to slow down.

 

[tugla]

around 75mph i get about 38-41 on highway..... and better at 65......

if its a cali bike they set them up a little more eco friendly and less power which im sure hurts it also....

 

[NHVmaxpower]

That's better than what I was getting. I would get if lucky n babied it 100 miles to a tank but was usually closer to96-99. I'd say leave it alone. Jmho

 

[tothemax93]

The milage is pretty good for 80-85 cruising IMO. Always good to do a tune up though. You can also change the final drive (pumpkin) to one off a yamaha venture. It has taller gearing, so it will keep your RPM's down a bit for better milage. Usually someone on the board will have a used one for sale. You can click the search button and type in, venture differential. a bunch of threads come up for the mod.:eusa_dance:

 

[DMAN999]

On my Stock Carbs with Supertrapps and a K&N Filter I get 25 mpg or so around town and while playing.
On the Highway I get around 33-36 mpg at the most.
Even when I had the Stock exhaust I got the same milage.

 

[MaxMidnight]

First step is to change air and fuel filter + plugs then synch carbs.

Also make sure that the tyres are at the correct pressure.

If you are really serious about improving fuel consumption then a skin tight leather suit may help.

As for the jetting, unless you know if it is running rich or lean and at which revs this occurs then any changes are based on guesswork.

If you want the jetting set up optimally then an investment into some dyno time would be prudent.

 

[m-cman]

My bike is completely stock except for the Venture rear end and I get around 44 mpg cruising about 75 or so.

It is possible the po changed jetting when installing the Supertrapps. Most here recommend going from stock 152.5 main jets to 150 when using slip-on mufflers. This is against conventional thinking which is why the po might have gone with larger jets.

Sean (one2dmax) has all the jets available for a great price. I would recommend verifying the jet size before going further. If you have 152.5 or larger mains, I would change to 150 and see what happens.

 

[Fire-medic]

my acquaintance w/a 1500+ cc flatslides & NOS installed is lucky to get 15 mpg. The closer to stock, the better the mileage.

 

[ninjaneer]

maintaining an 80-85 mph cruise, i would reckon your needles were more a factor than MJs. i'd try to lean the needles a bit. not sure how to do that on stock needles, though. matter of fact, if your trying to maintain a cruise with only 1/4 throttle, your AFR mix is more of a factor. in this case, turn the screws till the motor stumbles and then turn them out until it recovers. that's as best as you can do

but like the rest if guys have said 32ish mpgs is about the norm.


Regards from my Taptalking Hercules Android

 

[[email protected]]

If you are not afraid to dive in, I would pull the carbs off and open them up. Make sure everything is clean. SET THE FLOATS! Check the jets and if they are not stock, put stock ones in. Then, adjust the AF screws to be as lean as you can and still let the bike run. Synch the carbs once you get them back on the bike.

As noted, check tire pressure. A regular tune-up couldn't hurt if it hasn't been done.

 

[vmaxrooky]

my 1998 was getting 20-22 mpg these guys will help you out now I'm getting 36-38mpg with stock needles and stock jetting 2 1/2 turns out on the fuel air mixture, a K&N replacement filter and marks exhaust... before my bike was set-up way to rich/fat now shes running good and awesome mileage...Check out some of my threads and carb and fuel mileage theses guys helped me a bunch...not sure what a 1989 vmax should get?good luck to ya..Still tinkering around with jets and air/fuel mixture hoping to get a few more got to get my carbs sync'd also...