Two Stroke Motocross.com Forum

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General Two Stroke Talk / YZ 250 EFI

« on: May 13, 2013, 08:58:01 PM »

Would love to but at the moment the cost would be high. The Link computer cost $1500 NZD alone. Ultimately a computer board could be made to suit our application MUCH cheaper. At the moment we are just keen to prove this technology can work, In saying that if people are interested I will certainly consider making kits, but lets get some hours on this one first.

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General Two Stroke Talk / YZ 250 EFI

« on: May 12, 2013, 09:33:19 PM »

Tuning completely by plug and feel / sound at the moment. Injector timing is important, we have it set up similar to the Bighorn but can see this being optimized because the injectors are much closer to the transfer ports. Link is supposed to be developing new software to help, but appear to be to busy at the moment

. We still have a lot of options with what we have and this is what we will be playing with in the next while. With little runs like this including short full throttle squirts ( up the road ) the crank case seems oily on inspection but I want to set up the auto oiler before we go too much further, to be safe. I'm sick of having to walk out of trail rides ( early days of the Bighorn FI development ). It's a lot of fun to ride it certainly feels nicer down low speed than my standard YZ. This is the first time I've ridden it so I don't know about top end yet.
Oil in the fuel is no problem, modern injectors love it.

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General Two Stroke Talk / YZ 250 EFI

« on: May 12, 2013, 11:38:14 AM »

Here is a bit of test riding around the yard on Sunday. Might see if we can get the bike out on a trail ride this weekend ( with go pro ) perhaps. Fuel map is about right but injection timing needs more investigation also ignition timing is only approx. Nice to see it going so well so early on, Wayne is getting the hang of tuning by computer. There is not enough room to test in this yard but at least you can see it runs. Thanks to Dave for videoing the test run.

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General Two Stroke Talk / Explain this

« on: May 05, 2013, 09:04:38 PM »

Ha Ha, I used to ride one of these to work for years, didn't even hot it up, did I mention I like rotary valves? About 10 HP standard I think.
No actually It was a YB 100 Yamaha, similar lay out rotary valve engine

. It was a good reliable little commuter.

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General Two Stroke Talk / Explain this

« on: May 04, 2013, 08:59:44 PM »

A real twostroke.

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General Two Stroke Talk / YZ 250 EFI

« on: May 04, 2013, 08:31:26 AM »

It is interesting, on my Bighorn, just over fifty hours now including racing, I just use pre mix, 40 to 1, using ethanol is equates to about 20 to 1. I was worried about the lube situation but because of the position and timing of the injectors everything seems to stay oily, bigend, mains, rotary valve, etc. On the YZ the injectors are much higher up the transfers. So far it seems the oil still collects on the transfer walls and runs down to the mains and on to the bigend. It has only run an hour so we are still not sure. We have a small pulse pump ( about the size of an injector, able to be run by the computer ) that is on standby if we need it. We might have to squirt fuel down the inlet at high throttle setting yet but still early days. Head and barrel are coming off tomorrow for a first inspection. In the long run a small pump might be desirable anyway so mixing fuel is not required.

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General Two Stroke Talk / YZ 250 EFI

« on: May 04, 2013, 02:26:09 AM »

citabjockey, yes that's how we determined injectors were too big, apart from small "on time" numbers, was to disconnect one injector. I think two are still better and yes squish does a good job of mixing fuel air ( as a last resort ). The 450 stator has no problem with current delivery and yes a small battery ( lithium ion )is used strapped under the engine between the frame rails. Apparently just a capacitor will do the job but I'm not so sure. The bike is at the local Yamaha dealers place ( he owns it ) and he's been testing it under my guidance over the phone so far. Yes I NEED to get some video ( a friend of mine has just bought a Go Pro, so I might borrow that ). We have it fueling well down low, Yamaha dealer reports clean throttle up to 3/4.

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General Two Stroke Talk / YZ 250 EFI

« on: May 03, 2013, 03:41:50 AM »

Small change to the update, now it runs much better with the right injectors.

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Non-Moto / Motogirls

« on: May 03, 2013, 01:54:55 AM »

Grandad's mechanic, hey grandad I've just loosened some of your spokes

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General Two Stroke Talk / YZ 250 EFI

« on: May 03, 2013, 01:33:50 AM »

Yes, I'm not sure what to make of that post? The EFI YZ 250 is still going ahead, it is running ( not very well ) injectors are too big and we have had a hell of a problem getting a suitable ( small and reliable ) external HP pump but I hear it is heading out to a paddock to do some tuning this afternoon now we have smaller injectors. Drum throttle seems to work well. Just a small update.

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General Two Stroke Talk / Engine choice

« on: May 03, 2013, 01:26:31 AM »

Jeram, how to make a small fortune at motorcycle building start with a large fortune!

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General Two Stroke Talk / Engine choice

« on: May 02, 2013, 11:41:37 PM »

2T , that would appear to be both cranks turning the same way, 180 degree firing? On the 250 shown. Single idler in the middle ( clutch gear ). Same as this one only a 700cc. I had a lot of trouble with the gear to crank attachment on this engine. Perhaps the gears were just too small.
The three cylinder cases shown have the take off between cylinder 1 and 2
These are aviation engines with only a gear reduction. I have posted these before.
Make a great cafe racer engine ( three cylinder should be good for about 200HP ) Where would all the chambers go? Perhaps reverse the middle cylinder? Sorry don't want to hijack this post, just wouldn't it be a great project with a little time and money spare?

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General Two Stroke Talk / Engine choice

« on: May 02, 2013, 09:04:58 AM »

I think what you need is a Tandem twin 700cc, cylinders tilted at 30 / 40 degrees forward, gearbox underneath, one chamber forward and under the bike, other out under the seat. 140 HP. Chrome molly ladder frame and spoke wheels. Nice fat noisy chambers. Well that's what I would like! I've often thought about such a cafe racer. As 2T says anything with Rotary Valve.
Although I do have patterns for a three cylinder ( 1050cc ) case reed engine just needs a gearbox cases added to the pattern. I haven't owned a road bike in 30 years ( XS1100 last road bike ) and look at the modern road bikes with distaste, all the same. A large twostroke twin or three would be quite nice I'd say.
Good looking Honda though.

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