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May 8, 2007

Nytro Fuel Injection basics

Upon logging onto my email this morning I discovered some tragic news. An old friend, CJ Ramstad and his son JJ were killed in a head-on auto crash this past Sunday in Minneapo0lis. You probably know CJ most recently from his ramblings in Supertrax (Tailights) and ATV magazines or perhaps his amazing collection of vintage snowmobile photography accumulated throughout his long career in photojournalism. CJ has been a true supporter and activist for all things snowmobile for many years. Our deepest condolences from all of us here at Yamaha go out to his wife Karla and family.

On a lighter note, I have received a couple of inquiries regarding the fuel injection system and chain case on the new FX Nytro. Here’s some details on the FI layout, I’ll get some additional explanation on how it all comes together when next I have a chance to speak with our engineers.

picture1.jpgThe FI system is from Mikuni. It is described as a ‘return-less’ fuel system and features six sensors. They are: intake temperature, intake pressure, coolant temperature, throttle position, crankshaft position, oil pressure. The fuel pump is enclosed within the gas tank.

The information from these sensors is sent to the ECU where the running condition is compared to the pre-programmed ‘mapping’ contained in the ECU chip-set. The mapping program consists of predetermined ‘instructions’ for every possible combination of operation. The ECU then adjusts ignition timing, fuel meter and air flow to optimize power.
picture2.jpg The chain case is redesigned for lighter weight and increased rigidity surrounding the main shaft. A bearing is added to the end of the main shaft (in the cover) to optimize the shaft support. The attached diagram shows the standard chain case (left) and rpicture3.jpgeverse gear type (right) with the new bearing seen in the lower right hand side of the cover.

To help keep the weight down, the cover is cast from magnesium alloy.

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Posted @ 12:48 pm in Yamaha Insights   

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2 Responses to “Nytro Fuel Injection basics”

  1. Bob Hogg says:

    Too bad about CJ and son – that’s two snowmobile icons in as many years.

    No comments here yet, not much you can say about a chain case – so I will jump in as we really do enjoy the tech stuff.

    I have not followed Yamaha’s jack shaft history – but I’m assuming you put the outboard bearings on to make up for the lighter cases? After playing with a different brand this winter – it only further opened my eyes on how smart Yamaha is with building – for lack of a better word – a monocoupe type package. You have have parts supporting other parts rather than each part working on its own.

    There’s no doubt Yamaha engineers have done thousands of miles on the dual bearing setup and have resonance analysis on the design and it will work well.

    This may be off topic below – if it is, please delete.

    To me, like clutching, the jack shaft may disobey some engineering rules. I’ve seen – cause I’m old…some interesting ones.

    As a young kid in Quebec, I hitched hiked to boat races. My hero, Chuck Simon Canadian Champion, told me once they installed a bearing, to hopefully increase speed, mid way on the short shaft that connects the power head bearing to the prop gear case bearing. It broke the shaft, at the mid bearing in one race.

    Our race sleds started out with aluminum 7075 T4 jack shafts – math will tell you (not mine) a ½” O.D. steel shaft has less inertia than a 1” aluminum one. We cut down a stock steel jack shaft to about ½” O.D. and tapered the ends to full size at the bearings. We were worried, but we let it run free to resonate and had no problems on a sled with around 100HP.

    We had a company resonate test our Yamaha engine as the Cat clutch had a hum. The engine was equipped with a TZ ignition rotor, so the poor thing was confused. The test told us how much steel to hang on the clutch to make it happy. Anyway – this guy took me to a paper mill where he was testing the resonance of a 15’ long X 6 or 8”D hanging vertical steel shaft from a motor above. On the bottom was a 3’ Dia. propeller used for mixing paper stock. This shaft had no lower bearing – it ran free. He said a lower bearing support would rip the building apart!

    Interesting stuff Bob, I am wondering if the prop was a ‘chopper’ or a ‘cleaver’ 😉 … thx cr

  2. Yellowknife says:

    Hey Chris,

    Re: Fuel Mapping, I wasn’t able to fire up my Mountain Lite past -26 C, (cold start) which was unfortunate, and due to a poor fuel mixture at that temp and colder. The engine would easily turn-over however.

    How different is the Nytro’s fuel injection vs. that found on the 07 Mountain Lite? And if you have access to the technical specs, what’s the coldest temp that fuel map has in it for mixtures? The coldest I put my Renegade and Mountain Lite through (after being plugged in) was -44 C.


    The first thing that comes to mind is ‘what the heck are you doing riding at minus 44 degrees?’ You Arctic Men are tough SOB’s 😉 . Its funny but if I’m not mistaken, minus 44 is the bench mark engineering uses in engine development (I can’t speak to the Doo but sounds like they are in the same boat). The injection systems are quite similar between Phazer and Nytro but I understand the starting can be affected by compression and ECU mapping both of which are different on the Nytro and I wouldn’t be the least bit surprised if the 08 Phazers get tweaked in some areas to better cold starting. Can you plug in the rider as well as the sled? brrrrr cr

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