96 vmax bad mileage. (again)

[Jschl]

I've posted about this sled before and I know i am reaching at straws here but i have a 96 v max 600 that i love and hate not riding. This sled gets a reliable 5-6 mpg no matter of the riding style or conditions. We have torn the carbs down and rebuilt to spec., rebuilt the engine, put on a new clutch, checked the track tension, and even dropped the jets down to their lowest level (yet it still runs rich).This sled is fast and runs great, aside from a low speed burble, but nothing improves this sleds mileage.

As an act of desperation i was searching through the archives of the old rec.sport.snowmobiles newsgroup from the 90's and found some people with the same problem. They mentioned that Yamaha issued some sort of jetting revision for this motor that raised the mileage to a miserly 8-11 mpg. It looked like it had something to do with different needle jets or shims. Givin that most of these posts were 10-11 years old I couldn't follow up. Does anybody have more knowledge about this? Thanks

 

[yammy]

did you drop the mains or did you drop the needles or both? I had a 94 600 , it got around 8-9 mpg,I put a set of psi pipes and dropped the needles one notch,and got 10-11 mpg.you have to be sure to set them up right,clutching,skid,jetting, etc...to get 10 mpg, but thats all you can expect to get out of that hog! Daman knows those sleds real well ...i'm sure he'll chime in and give you specific info!

 

[Jschl]

The needles are dropped to the lowest levels, so it's jetted for the mountains....yet it still the seems to run rich at sea level.

We've all but given up on this sled but every year the bug still bites. In all honesty 8mpg is the goal, but we'll probably never get there.

Thanks!

 

[Yammi Nut]

mileage

hi, I had the same problem on a 97 V Max 600 talked to some Yamaha mechanics and they recomended that I change the needle jets and nozzels together. I don't know wether you have done this but it improved my mileage by a great deal. Yammi Nut

 

[crewchief47]

The needles are dropped to the lowest levels, so it's jetted for the mountains....yet it still the seems to run rich at sea level.

We've all but given up on this sled but every year the bug still bites. In all honesty 8mpg is the goal, but we'll probably never get there.

Thanks!

Lets clear up what you mean by that needle statement. Did you drop the needles by raising the clip? Or did you lower the clip?

You didn't mention if you've inspected the reeds. I see you said re-build, did you replace the reeds? Has the mileage always been bad? Or has it gotten progressively worse?

Would be helpful if you posted the jet sizes, pilot and main, and the position of the needle clip. Also the float height. You mention a new clutch which I assume means Primary, is it a stock or aftermarket clutch? What weights and rollers? Is it hard on belts? Are you using the Yamaha belt? Is the Secondary in good shape?

 

[Jschl]

Sorry for not being more descriptive, The clip is on the highest setting, so the needle is low. I believe the main jets are 152.5. Checking the plugs they are still mostly black and tan. As far as clutching goes, We replaced the primary clutch. I don't remember what the weights and rollers were (that was replaced last year), but it was a comit clutch and set up to resemble stock. The original clutch was stock. It has never been hard on belts. As far as my I can tell the secondary works properly.

That's the info i have off the top of my head, it's been a 3 year project and I keep the sled at my dad's house so not easily accessible today (he is the head mechanic on it anyway). We have been through everything a hundred times, to the point where we have all but given up and dedicated it as a sled just to keep to run around the farm. I have had it to several dealers and they all say it looks good or some bull story about how they have cleaned the carbs and it will run better now.

The thing that got me asking questions was running across this statement on an old newsgroup from 1999:
------------------------
"Had the same problem with my '95, as well as terrible (< 7 mpg) milage. Then
during one trip to my dealer, the service manager informed me of a tech update
that dealt with the needle position. If i remember right, the stock setting
includes a single shim, whereas the update mods to two thinner shims for more
precise tuning.

Check with your dealer for sure, but since the update on my 600, very smooth
through the entire range, and 10+ mpg. "
--------------------------

I figured i would bring it up on here to see if anyone remembered such a thing. Thanks for your help. I might give what yammi nut said a try. If i can can bring myself to put more money in this thing.