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Author Topic: YZ 250 EFI  (Read 57058 times)

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Offline Stusmoke

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YZ 250 EFI
« Reply #240 on: August 14, 2013, 09:41:17 AM »
Ha Ha Ha, sell the idea to Yamaha, their NZ technical guy seems not even interested. It's been waved under his nose. They are not interested!
That's the encouraging thing about this " conversion" there has been almost no problems. I made the throttle drum too good a fit and sometimes the throttle would hook up for a moment, not nice going into a corner with trees everywhere. Giving it a little clearance has fixed that problem. I gave the head too much compression ( if some is good, more must be better ) but that was quickly rectified, my fault. We have broken two kick start shafts now with the original ignition ( through the LINK ), at kick over the computer looses count of the flywheel pins and gets mixed up and then fires at the wrong time. We fixed this by fitting an Ignitec and using the LINK for fuel only. I made a new kick start shaft out of EN39B and case hardened it. Something else will bust now because the shaft never will anyway there is no kick back problem now with the Ignitec. I'm waiting on an Ignijet computer to try out, this should do the same job out of a much smaller package and much smaller price! That's about it, ride it in the rain, doesn't bother it. We are using a crude oiler system still, runs 60 to 1 oil in the fuel plus after 60% throttle a small valve opens to a fixed jet in the throttle body.

Shows how clever they are then. Imagine if they bought it, threw a million dollars of testing at it and dropped it on the market in 2015. Can you say sales rush? They'd go from not beng able to afford a factory effort to being able to forward five. You've clearly put alot of effort in, and I'm sure it was a fun project. Plus rewarding as balls  :o I know I've enjoyed reading about it.

With the appropriate mapping changes, hopefully that 250Fness can be persuaded out of it :D I've always said a 250 two stroke is like a 250F on some serious roids but does it all at an engine saving RPM.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »

Offline citabjockey

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YZ 250 EFI
« Reply #241 on: August 14, 2013, 03:42:42 PM »
you could write a book on your experience with the BigHorn, and this YZ. I have a great time reading about these technical details. An ignition problem that breaks the shaft. Who would have thought? Does the flywheel have a "TDC" pin such that on start the LINK can wait for that and then start sparking? Or maybe thats how it was supposed to do it anyway?

Can you refresh my memory -- you were looking at a more reasonably priced computer. I don't think that is the LINK. Did that ever go anywhere?

Ha Ha Ha, sell the idea to Yamaha, their NZ technical guy seems not even interested. It's been waved under his nose. They are not interested!
That's the encouraging thing about this " conversion" there has been almost no problems. I made the throttle drum too good a fit and sometimes the throttle would hook up for a moment, not nice going into a corner with trees everywhere. Giving it a little clearance has fixed that problem. I gave the head too much compression ( if some is good, more must be better ) but that was quickly rectified, my fault. We have broken two kick start shafts now with the original ignition ( through the LINK ), at kick over the computer looses count of the flywheel pins and gets mixed up and then fires at the wrong time. We fixed this by fitting an Ignitec and using the LINK for fuel only. I made a new kick start shaft out of EN39B and case hardened it. Something else will bust now because the shaft never will anyway there is no kick back problem now with the Ignitec. I'm waiting on an Ignijet computer to try out, this should do the same job out of a much smaller package and much smaller price! That's about it, ride it in the rain, doesn't bother it. We are using a crude oiler system still, runs 60 to 1 oil in the fuel plus after 60% throttle a small valve opens to a fixed jet in the throttle body.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
Yamaha CT3, RT3, MX125, SC500, Toy Prius, Diesel F250 (it all balances out)

Offline lauterbacher

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YZ 250 EFI
« Reply #242 on: August 14, 2013, 07:13:23 PM »
Uniflow you were going to do some more dyno tuning when you got the jetting by computer corrected, any chance yet. and is this 250 motor a stock unit with just the EFI on it. thanks
« Last Edit: December 31, 1969, 04:00:00 PM by ' »

Offline Uniflow

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« Reply #243 on: August 14, 2013, 09:25:02 PM »
Not stock, FMF pipe, V force reeds and one of my toroidal heads but other than that it's stock, no cylinder work. 
Yes the flywheel has a 12 minus 1 pin setup ( eleven pins and a gap ) on it, the -1 ( missing pin ) is to give the computer a heads up that it's done a turn and is ready for another cycle. The computer not only counts the pins but also the time between them so at kick over there can be potential miss calculation. The moment it fires it will correct itself. The gap does not necessarily have to be at TDC as you can tell the computer the degrees from the gap to TDC, it will sort itself out. There are many ways around this but an Ignitec was an easy fix as I have them spare on the shelf, better spark too. 
The LINK is a good computer but this new Ignjet should do as well at a much cheaper price, we will see. It's taken an unbelievable time to get hold of one, the order has been in for months.
Write a book, I hate writing!
« Last Edit: December 31, 1969, 04:00:00 PM by ' »

Offline _X_

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« Reply #244 on: August 14, 2013, 09:31:55 PM »
how about a documentary? all you have to do is talk, drink and talk some more and we dont have to read.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »

Offline citabjockey

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« Reply #245 on: August 14, 2013, 09:42:13 PM »

Write a book, I hate writing!

Then what the heck are you doing with all this posting???? If I am not mistaken it qualifies!  ;-)

So I can't believe that LINK can't wait for a full rotation (or at least till that gap comes around) to start sparking. Who the heck wrote the firmware???


« Last Edit: December 31, 1969, 04:00:00 PM by ' »
Yamaha CT3, RT3, MX125, SC500, Toy Prius, Diesel F250 (it all balances out)

Offline Lolerbabop

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« Reply #246 on: August 14, 2013, 09:47:33 PM »
« Last Edit: December 31, 1969, 04:00:00 PM by ' »

Offline Stusmoke

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« Reply #247 on: August 14, 2013, 11:16:37 PM »

Write a book, I hate writing!

Then what the heck are you doing with all this posting???? If I am not mistaken it qualifies!  ;-)

So I can't believe that LINK can't wait for a full rotation (or at least till that gap comes around) to start sparking. Who the heck wrote the firmware???




Probably Apple... They're my go to blame for anything tech. Like honda in anything motor :D

So if theres a miscalculation when kicking over, does this make it a bitch to get started?I know that the RMZs first couple years on EFI made them even worse to start. Actually that pretty much goes for all of them...
« Last Edit: December 31, 1969, 04:00:00 PM by ' »

Offline GerbilGronk

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« Reply #248 on: August 15, 2013, 05:54:14 AM »
how about a documentary? all you have to do is talk, drink and talk some more and we don't have to read.

Great idea. We need an armchair an open fire a pipe and a pair of comfortable slippers.

 The EFI sounds quite different. In a good way. It looks like it hooks up really well. Looks easier to ride.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »

Offline Stusmoke

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« Reply #249 on: August 15, 2013, 06:05:17 AM »
how about a documentary? all you have to do is talk, drink and talk some more and we don't have to read.

Great idea. We need an armchair an open fire a pipe and a pair of comfortable slippers.

 The EFI sounds quite different. In a good way. It looks like it hooks up really well. Looks easier to ride.

On the bad news side, that pretty much writes off the four strokes only real advantage in the lites class.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »

Offline Jeram

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« Reply #250 on: September 02, 2013, 11:36:06 AM »
20% less fuel burn this weekend. It depends on the type of usage, at lower speeds ( tighter track ) there is a larger benefit, more top end running = less fuel saving. I would imagine top out both bikes would be similar fuel consumption ( similar power ). Now it's getting exciting, every time out on the EFI bike is a little better as we change settings slightly. This weekend we got the raspy original feel back ( like my standard bike ) but we soon tuned that back out! It's much better / faster to ride with the smooth program installed. We even had a 250F rider have a go on the bike, he was quite shocked at how it went, it was hard to pry him off the bike after that. 

With this torquey, tractable powerband, would it be possible to increase the revability of the 250 two stroke? Most are typically the midrange monsters as we know, but how about revving them out to their redline? And possible a slightly shorter stroke/bigger bore design to increase said redline?

MX seems to be the exception to the two stroke bore/stroke rule of thumb.

square bore/stroke is almost always optimal except for in moto-cross.

I always wonder why the didnt build the optimal 68x68mm 250-2T and then achieve the required bottom end/mid range/top end balance with pipe design and porting....

I am sure there is a very valid reason and it likely has nothing to do with HP, but more likely about usability and traction... and even more likely; laptimes.....

I always thought it was a traction issue. Whats the standard bore/stroke of the 250t offroad motor? 66.4x74 or something? 6mm off the stroke compensated for by a 1.6mm increase in bore, wouldn't that mean an increased turnover speed? 250 2ts struggle for traction in alot of places as they are, I always just put it down to a turnover speed too quick for the dirt. Four strokes can get away with it because they deliver a power stroke half as often.

72

« Last Edit: December 31, 1969, 04:00:00 PM by ' »

Offline Stusmoke

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« Reply #251 on: September 02, 2013, 11:45:16 AM »
I thought that had too many fours in it.... My bad.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »

Offline SachsGS

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« Reply #252 on: September 02, 2013, 02:45:24 PM »
It was Maico that pioneered the 72 mm stroke.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »

Offline bearorso

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« Reply #253 on: September 02, 2013, 06:32:45 PM »
And then you get the various 2t Trials Bike Engines - most of which are quite oversquare.

Yet, they are Torque / soft(er) power oriented.

Optimal bore and stroke - it depends on a designers particular 'bent'. And each and every bloody one would argue furiously for their 'optimal' ratio.

Maico 250s, for a few decades, have had the 67 / 70 bore and stroke. My 320s had 76 x 70. When they had 72 stroke, and abandoned it, I have no idea. They may have 'pioneered' it, but they  sure didn't stick with it.

Maicos fabled 490 /500 engines, were never a square design - both being a slightly oversquare engine. I think the one '500' that I know of, with a 'square' engine, is the KX500, at 84 x 84. Though, I'd not be surprised to be informed of other '500s' that are square engines.

 Open Class 2t MXers, had such a surfiet of power and torque for their times, they were bouncing around with inumerable bore stroke ratios, when they were common.

4ts keep going for more and more revs, for getting their HP. So, more and more oversquare.

The 2t design, is so interweaved within itself  - bore / stroke / crankcase volume / porting as making up the whole induction, and exhaust cycles, as to be incredibly varied in how it's done.

Someone coming out with "this is optimum", I just think of as one who has picked his 'favourite' - or, is subscribing to their particular worship of  a designer / brand / model.

There is quite some arguement that 2ts will go to more oversquare engines, especially with such techs as DFI, as the fuel component of the charge, will be less dependent on the 'whole engine' concept.

I think, for quite some time, the Evinrude E tech outboards have been based on a fairly oversquare ratio. It seems to be 96mm x 76mm for the V6s, and 91 x 66 with the V4s and inline engines. Of course, these engines are used in a much different context.

« Last Edit: December 31, 1969, 04:00:00 PM by ' »

Offline Stusmoke

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YZ 250 EFI
« Reply #254 on: September 03, 2013, 12:47:11 AM »
And then you get the various 2t Trials Bike Engines - most of which are quite oversquare.

Yet, they are Torque / soft(er) power oriented.

Optimal bore and stroke - it depends on a designers particular 'bent'. And each and every bloody one would argue furiously for their 'optimal' ratio.

Maico 250s, for a few decades, have had the 67 / 70 bore and stroke. My 320s had 76 x 70. When they had 72 stroke, and abandoned it, I have no idea. They may have 'pioneered' it, but they  sure didn't stick with it.

Maicos fabled 490 /500 engines, were never a square design - both being a slightly oversquare engine. I think the one '500' that I know of, with a 'square' engine, is the KX500, at 84 x 84. Though, I'd not be surprised to be informed of other '500s' that are square engines.

 Open Class 2t MXers, had such a surfiet of power and torque for their times, they were bouncing around with inumerable bore stroke ratios, when they were common.

4ts keep going for more and more revs, for getting their HP. So, more and more oversquare.

The 2t design, is so interweaved within itself  - bore / stroke / crankcase volume / porting as making up the whole induction, and exhaust cycles, as to be incredibly varied in how it's done.

Someone coming out with "this is optimum", I just think of as one who has picked his 'favourite' - or, is subscribing to their particular worship of  a designer / brand / model.

There is quite some arguement that 2ts will go to more oversquare engines, especially with such techs as DFI, as the fuel component of the charge, will be less dependent on the 'whole engine' concept.

I think, for quite some time, the Evinrude E tech outboards have been based on a fairly oversquare ratio. It seems to be 96mm x 76mm for the V6s, and 91 x 66 with the V4s and inline engines. Of course, these engines are used in a much different context.



I hadn't considered the crankcase volume and pressure implications of a motors bore/stroke but it makes sense. Like you said, using an electronic injection method, direct or not, turns it into a whole nother board game. If this rumoured 2014 DI 250 two stroke turns out to be true it will be interesting to see where things go.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »