Making a 2 smoke run backwards.

[Boostinjdm]

STARTER MOTOR NOT TURNING IN RIGHT DIRECTION: The starter motor has nothing to do with perc. perc works by slowing an already running motor down low enough, then firing far enough below t.d.c. to make the motor spin the other way. The motor has to be running in forward first. perc works with or without a starter, the starter has no effect on it

True in a PERC system.  But in a homebrew, you may have to kill the motor dead and then start it spinning in the opposite direction.  This is where I feel the second starter may be needed as the bendix only functions in one direction.

[Boostinjdm]

CDI AND RETARDED IGNITION IN REVERSE: You must use a perc ignition, there is no other way to make it work. yes, older points style 2 strokes would often start in reverse, but it won't work with a cdi sled motor

Please elaborate. 

The way I understand it is that the engine and CDI do not know which direction the engine is rotating.  The important thing is the relation of the trigger to TDC.  If the trigger is advanced in forward rotation then it would be retarded in reverse and the engine prolly won't run.  My proposed solution to this is to add a second trigger that will be selected by a relay and a "Reverse" switch on the dash.  The relay would be used to select which trigger is feeding the CDI information.  Only one would be in use at a time.  So the way I see it is that you would have the proper advance in either direction by simply selecting the trigger that has the correct relation to tdc.

[b.c.bugger]

dude, honestly. Buy a kit. It will come with a new c.d.i. You need the reverse cdi to make the timing work right. I know of no other way to make it work. You cannot just program your own cdi to fire in reverse. I know a lot of people who have done this kit and I have never heard of anyone trying to "homebrew" it, it wouldn't be worth it. Some things have to be bought. You can buy a kit on e-bay. Very worthwhile i.m.o.

[Boostinjdm]

#1.   I have not found a kit for my engine.
#2.  The kits I have found (that don't work for my engine) cost as much or more than I could replace this engine with a 4stroke for.  Still wouldn't have reverse, but I would be happy.
#3.  If the answer was always "just buy a kit", nothing new would ever be built, most of those kits wouldn't exist, and this would be a retail support site.

I had an idea and was looking for input on how to work it out for myself.  Buying a kit is not helpful, unless you want to buy it, dissassemble it, then report back to me how it works.

This is not a personal attack, I am just trying to express my viewpoint.
And I never said program, modify, or build a CDI.  Just alter it's inputs.  The CDI won't know the difference, but whether or not the engine runs depends on it.

[Voodoochikin04]

so far everything point you have made appears to be valid. running in reverse the cdi would read it as retarded, so the second trigger would appear to be advanced. sounds valid.. but what do i know. hope you make it work. good luck.

[Boostinjdm]

Exactly, thank you.

Actually the CDI doesn't even know it's retarded ,  the engine just won't run or run right because the spark is retarded in relation to TDC.  Now I'm splitting hairs....

[b.c.bugger]

boostin, I'm just trying to make it simple for you. Maybe it would be possible to do what you are asking without a kit, maybe not. I am around sleds every day and have never heard of somebody making their own reverse kit.
I don't know what motor you are running but here's one I found on e-bay
http://cgi.ebay.ca/NEW-POLARIS-ELECTRIC-700-XC-XCSP-REVERSE-KIT-2874618_W0QQitemZ310131884827QQcmdZViewItemQQptZSnowmobile_Parts_Accessories?hash=item310131884827&_trksid=p3286.c0.m14&_trkparms=72%3A1215%7C66%3A2%7C65%3A12%7C39%3A1%7C240%3A1318
If you were to just buy the secondary clutch alone by itself it could run you $500 for a new oem unit, so I would consider this a pretty good bargain for a complete assembly.

[Admin]

IM O the engine should run in reverse without any mods, the timing will be retarted, but the mpem will still get juice, as the stator doesnt care which way it is turning either, Especially on a rotary engine I would be premixing the gas anyhow, so fxxk the oil pump all together... what you need to do is take off the pull starter, and start it up manually with a rope in reverses, there is absolutely no reason it should not work...

[thedoctor]

I am not that familiar with twin sled motors, but I had a 1973 Yamaha 250mx that would run in reverse. Sometimes it would start in reverse, sometimes it would idle low and change direction. It ran well enough in reverse to scare the crap out of me  [imagine hill]. Low idle and timing were only things needed to reverse. I think [scary process] your idea would work. The secondary is the only problem, but two sided ramps should cure that. Buy used secondary off rer sled. Good luck. Think outside box. Tim

[lee1969GB]

I have not read all of this thread so please excuse me if I repete.
I have a 800 rotax engine with RER from a ski doo. it amazing how it works, I thought you would have to turn off the engine then re start it in reverse but no, you just press the button and the engine slows down stops for a millisecond then runs backwards, press it again and it goes forwards again. Not sure how the oil pump copes but I am told it works 2 way and I would assume the water pump works in the same way.
When I was trying to get the RER set up I tried to pull start it whilst a friend was pressing the RER button, big mistake it backfired and broke the pull starter.
I am suprised these engines are not used more in mini buggys because of the expence of FNR boxes and they do go well.
Someone said that harley did a four stroke engine that runs backwards but I do not see how it can be done because the valve timeing would be way out, but I am not one to shoot down an idea I do not fully understand.
Maybe it could be done by putting the pick up on some sort of slider so you could pull a lever and it moves the pick up to the other side of top dead center?

[fabr]

A 2 smoke doesn't care what rotation it is.All that is needed is a means of altering the input signal.Think -second pickup-switch from one to the other.Spin engine in the direction you want and there ya go.You guys are making too big a deal of this.Boost ,your idea is valid and will work. All you need to do is have the second trigger that can be selected via toggle switch. The engine and electronics don't care what the direction of rotation is.  All you need is a properly positioned second trigger.

[SPEC]

In the early seventies Harley/amf made a golf kart...That spun the motor backwards for reverse, I knew a guy that had one...I think master hit it on the head 2 pickups and a switch...I think it reversed polarity...I was prolly about 10 or 11 when I saw/rode in it...It wasn't fast so I didn't have much interest in it at the time
I had a John deere A that you had to spin the flywheel by hand to start....That fooker ran as well backwards as it did forewards...Really mess a guy up at 4 am. when put in gear and it goes the wrong way...

[Admin]

the 2 stroke golf carts have a dual polarity starter, they start in either direction... I believe you wouldnt even need to alter the timing pickup, as it is timed via the mpem on newer motors anyhow...

[fabr]

Many starter can be made a 2 way.Problem is that it will only have 1/2 the power.

The signal is still just a reference point.You will need a correctly positioned reverse pickup to have it run right. Then all the stuff after that will correctly time the spark. I'm not saying it WON'T run (like crap)without doing so tho.

[Admin]

and a starter with a bendix or the tech term for when the gear slides out wont work tho, right, as it wont throw the gear... Typical sled starters are just that. The old golf carts used starter generators, and all they did is reverse the polarity... Im guessing a guru could add a switch to the mpem to alter the timing electronically, as i am sure that is how it is done in the newer sleds anyhow... then there would be no need for another pickup, all tho i may be very inacurate, as i believe the rer motors do indeed have a different stator and flywheel...