YZ 250 EFI

[TMKIWI]

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I still have a bit of , faith in Yamaha - they at least have kept producing, and supplying to most world markets, 2t MXers. I live in hope, that the company that put reed valves and good porting into their production 2ts, of all types, over 40 years ago, then the single shock, and so many other things - including having the balls to mass produce 4ts that were not Foo Foo bikes, will be the first Japanese manufacturer to give us a modern 2t.

You may be right. My local Yamaha dealer told me the other day that Yamaha was bringing out a EFI YZ250 for 2015.
Who knows if it an internet rumor or not. Would be nice to see it happen.

[bearorso]

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I still have a bit of , faith in Yamaha - they at least have kept producing, and supplying to most world markets, 2t MXers. I live in hope, that the company that put reed valves and good porting into their production 2ts, of all types, over 40 years ago, then the single shock, and so many other things - including having the balls to mass produce 4ts that were not Foo Foo bikes, will be the first Japanese manufacturer to give us a modern 2t.

You may be right. My local Yamaha dealer told me the other day that Yamaha was bringing out a EFI YZ250 for 2015.
Who knows if it an internet rumor or not. Would be nice to see it happen.

Just give thought to the sort of sales Yamaha would get from such a bike. Just for a moment, cogitate on it........

They've made serious profits on the current alloy framed 125s and 250s, with the prices they've charged. They've 'milked' them for all they're worth, for many years now. If they didn't "go the gouge" on  'EFI / DFI / whatever the bloody things turn out to be', New 2ts, They'd sell a Lot of bikes. And that's what you'd think they'd want, in these straightened times for bike sales.

Hmmm, I wonder if they'd apply the reverse cylinder idea to such a "dream bike"? It would be logical, with their 4t MXers having gone that way. I, personally, think it's a very good set up (too many Drongos have equated JS's record on the reverse 450 as it being his "problem" - well, I guess the RMZ is a "POS", too?), that would enable so many benefits to 2ts. Tiny little Ossa, showed a great template for future 2ts. Just getting the pipe out of most harms way, would be a great thing.

[Uniflow]

No one want's to take a risk in this financial environment. Remember to rotary engine debacle, late 70's.

[bearorso]

I really see no risk in doing modern 2ts, that will pass legislation. Or ones that may not, such as just pre reed EFI, with regards to MXers. Most solutions are being sat on, and the placing of a 2t in an existing 4t chassis, can be done at minimal expense.

If you , Uniflow, can do a EFI 2t - that is far more sophisticated than just the placement of an 'electronic carburettor', which is so prevalent now, as to be of little expense, it's not much of an ask, for a major manufacturer to put such basic tech (I emphasize the 'electronic carb, that EFI basically is - not your impressive transfer port / case injection efforts) on a 2t.

  Frankly, I think the   Biggest Risk for manufacturers, is to not make a return, at least partially, to 2 Stroke production.

Rotary Debacle? With relation to bikes, Suzuki's RE5, Yamaha's never produced Rotary ( and their never produced, road going inline , pistoned Four cylinder 2t that the TZ 700 /750 were supposed to be 'race versions of, for the F750 class) Van Veen's OCR(?), Hercules / Sachs , Nortons  (great track record, for such  small operations, in both Race teams) Rotaries, were not debacle, just a branch of motorcycle engines, that was barely touched on. I know bugger all about the car market, but I don't recall lots of manufacturers, going for Rotaries, and losing their shirts over them?

 But, I may have easily missed such a 'debacle' - as I said, I'm not particularly car orientated. Two Wheels have always been my passion - 4 or more, transportation, is all.

It's funny, my little suburb against the mountain, seems to have a bit of a RE(?) 8 cult  going - I know of at least 9 of them being nearby  ......... I love how my  two V8 worshiping / Drag Racing brothers nearly foam at the mouth at the sound ( or even sight) of them! 

[Stusmoke]

.

I still have a bit of , faith in Yamaha - they at least have kept producing, and supplying to most world markets, 2t MXers. I live in hope, that the company that put reed valves and good porting into their production 2ts, of all types, over 40 years ago, then the single shock, and so many other things - including having the balls to mass produce 4ts that were not Foo Foo bikes, will be the first Japanese manufacturer to give us a modern 2t.

You may be right. My local Yamaha dealer told me the other day that Yamaha was bringing out a EFI YZ250 for 2015.
Who knows if it an internet rumor or not. Would be nice to see it happen.

Just give thought to the sort of sales Yamaha would get from such a bike. Just for a moment, cogitate on it........

They've made serious profits on the current alloy framed 125s and 250s, with the prices they've charged. They've 'milked' them for all they're worth, for many years now. If they didn't "go the gouge" on  'EFI / DFI / whatever the bloody things turn out to be', New 2ts, They'd sell a Lot of bikes. And that's what you'd think they'd want, in these straightened times for bike sales.

Hmmm, I wonder if they'd apply the reverse cylinder idea to such a "dream bike"? It would be logical, with their 4t MXers having gone that way. I, personally, think it's a very good set up (too many Drongos have equated JS's record on the reverse 450 as it being his "problem" - well, I guess the RMZ is a "POS", too?), that would enable so many benefits to 2ts. Tiny little Ossa, showed a great template for future 2ts. Just getting the pipe out of most harms way, would be a great thing.

Absolutely. Think about how many Loyal (And ecstatic) customers of there are of the current "outdated" YZ250/125. Its one of the best motocross bikes every made. Imagine how many of those customers would line up for an updated YZ250/125 off the production floor, E/DFI or not.

The reverse cylinder idea was and still is a good one. The YZ450F of 2010-2013 (possibly 2014 yet, who knows) was a good, reliable bike that had issues. Name me a motorcycle that DOESN'T have issues. Oh yeah, the YZ250 and SX250.... OOps 

Seriously though, it was VERY wrong of James AND his mechanical crew to be slinging **** at the YZF. He broke his contract to get away from it, thats all that needed to be said. Going on radio and dissing out your previous employer at his level of racing is just plain wrong IMHO. And as bearoso said, hes still just as ****ty if not worse on the best turning bike in the biz.

[Nath88]

Awesome project Uniflow!
I'm looking at doing a similar thing with my registered 02 YZ250 motard, primary injector in the transfer for idle and light load, secondary in the throttle body to keep the crankcase cool. What oil pump are you using? I've been looking for a small one for a while, I even designed one for a final year engineering project, but wasn't very successful. Oil pump would be awesome on the street, stock tank gives me about 100km range

[Stusmoke]

Awesome project Uniquip!
I'm looking at doing a similar thing with my registered 02 YZ250 motard, primary injector in the transfer for idle and light load, secondary in the throttle body to keep the crankcase cool. What oil pump are you using? I've been looking for a small one for a while, I even designed one for a final year engineering project, but wasn't very successful. Oil pump would be awesome on the street, stock tank gives me about 100km range

Good to have another expert on here, welcome aboard! To be clear, I wasn't calling myself an expert.

[Uniflow]

The YZ is using a small jet into the intake stream just behind the throttle body. It's programed to only open after 60% throttle. Works well. Although I'm designing a smaller electric ( UCU ) driven pump, smaller than a match box for accurate oiling, this will be feed straight to the bigend.

[Stusmoke]

The YZ is using a small jet into the intake stream just behind the throttle body. It's programed to only open after 60% throttle. Works well. Although I'm designing a smaller electric ( UCU ) driven pump, smaller than a match box for accurate oiling, this will be feed straight to the bigend.

Does that mean it will be "four strokeized"? As in a sump to lube big end/Mbearings, and an oil spray to lube top end? Does that mean that the vaccum operation of the two stroke will be completely throw out the window in favour of a fuel pump? Seems a shame, its such a good idea.

[Uniflow]

No, twostroke design stays the same, just directing the lube oil straight to where it's most needed ( first ). The problem with the bigend is it not only needs oil but more importantly it needs cooling from the rollers rubbing on the cage. Modern cages are silver plated to minimize friction and maximize heat dispersion away from the rollers edge. Fuel is a good cooling agent but so is air ( perhaps not quite as good ) but with oil ( the normal amount that would be run through pre mix ) pushed straight into the bigend and air, it's effect is nearly as good. Well so far so good anyway. Main bearings are easily sealed off from the crank case and can run in there own oil bath.

[TMKIWI]

Main bearings are easily sealed off from the crank case and can run in there own oil bath.

So you wont be running a total loss system then. Or a bit of both.?

[Uniflow]

No unfortunately, it will be a bit of both but overall should be less oil heading out the exhaust. 

[Stusmoke]

No unfortunately, it will be a bit of both but overall should be less oil heading out the exhaust. 

I call that a win then. So when you say oil that would normally be run through premix is pushed straight into the bigend and air, do you mean an oil jet spraying into the crankcases and onto the big end? If so, does that mean dropping premix entirely?

[Nath88]

The YZ is using a small jet into the intake stream just behind the throttle body. It's programed to only open after 60% throttle. Works well. Although I'm designing a smaller electric ( UCU ) driven pump, smaller than a match box for accurate oiling, this will be feed straight to the bigend.

Clever, I've been looking at the Aprilia oil pulse pump 8222708 from the '00-'04 SR50 Ditech and '04-'08 SR50 Ditech Factory, pretty much fits your description. $126 new from AF1 Racing. Pulse from ecu based on load and rpm should be perfect.


The flow rate should be enough to supply the 250, it's capable of much more than the 50 requires to allow rapid bleeding of the oil lines. Would have liked to have found this before designing an oil pump, could have done my project on the actual injection system which would have been a lot more rewarding.

So you intend to plumb directly to the big end feed holes in the crankcase and let it disperse into the top end from the crank spinning? I'm imagining some little brass feed tubes from around the reed cage area then into the feed holes, but I'd be concerned about them breaking off with vibration, maybe some silicone hose might be appropriate. How will the pressure pulses in the crankcase affect the pump?

[citabjockey]

Would this pump need to feed tunnels in the crank itself to get oil to the big end bearing?
So if you put the main bearings "outside" the seals (then is the ignition in an oil bath?) then have a trench in the case and a corresponding hole in the crankshaft so the pump can feel oil into the crank. Then it can make its way to the big end bearing. Would there also be a need to supply oil to the wrist pin bearing? I wonder how SkiDoo does this?

Of course this whole setup could also supply main bearings if left inside of the seals.