KDXRIDER.NET

Surely this can't be good...

Lately riding, on steep hillclimbs, sometimes I'll stall the bike and while I'm sitting there and the bike rolls backwards a little bit, sometimes it try to start.

I've heard of two smokes starting up backwards. But I've never let it happen, sure as hell don't want the bike to take of in reverse!

Once this weekend I was trying to turn my bike around in a real tight spot and I killed the motor. I reefed on the bars backwards and my clutch was dragging a little and the motor fired up. I let out the clutch and to my surprise the bike went forward. I told Jerry about it, and he could not explain it.

Later on, on a big hillclimb, it did it again. The next time I met up with Brad and Jerry I pulled up next to them and told them to explain this to me. With the motor off bike in first gear I just barely reefed on the bars backwards and my bike instantly started up and went forward

I wish we would have video taped it

I've had that before..... I'm as clueless as you are unfortunately.

I had a bike that would frequently start backwards. The first time it happened was after a pretty spectacular crash, where I had been in the air and landed backwards. When I got up and started it with the kickstarter everything seemed normal and I was primed to get back into the race, leaning forward to control it I dumped the clutch and the thing rocketed out from under me, dumping me over the bars onto my head.
I started it again, and slipped the clutch just a bit to see which way it wanted to go, but all was fine and she wanted to go forward. After that it seemed it would start backwards about 10% of the time. Nothing like having confidence in the simplest things... Somebody once told me long after I got rid of it that it might have been timed too close to TDC. Don't know if that's true or not.

Mine starts backwards but it runs forwards

Don't touch a thang! That's a helluva feature to have!

Could it have something to do with pulling it through a compression stroke and it firing the piston back into the proper direction ?

Sheet...that's a weird one!

Colorado Mike wrote: . . . When I got up and started it with the kickstarter everything seemed normal and I was primed to get back into the race, leaning forward to control it I dumped the clutch and the thing rocketed out from under me, dumping me over the bars onto my head . . .

THAT would have been an America's Funniest Video grand prize winner!

GS wrote:Don't touch a thang! That's a helluva feature to have!

Could it have something to do with pulling it through a compression stroke and it firing the piston back into the proper direction ?

Sheet...that's a weird one!

Even wierder, it starts with the bike only moving a foot or so. Push starting in forward takes a lot more effort

How about this:

Get on an incline and roll backwards, bump-start it in reverse, pull in the clutch, turn the bike around quickly as you roll downhill perhaps using the front brake to make it slide so the front wheel is pointing downhill, dump the clutch, and take off down the hill moving in a forward direction . . .

a Starsky & Hutch move . . .

have somebody take a video, post a link, and I'll donate $20 to kdxrider!! ANYBODY ELSE WILLING TO DONATE TO SEE IT??

If it goes wrong, continues to operate in reverse and thusly flinging you over the handlebars, I'll increase the donation to $50!!

He did it over and over and over. It was not a 'freak' thing.

IF spark timing was ATDC, that would explain it, right? That would make a bump start when moving backwards tend to fire the engine 'forward'.

No matter how close it was to TDC, as long as it's still BTDC, it's going to tend to fire the engine 'backwards'.

Terms 'backward' and 'forward' relating to what the transmission is doing, of course. The engine itself doesn't care, OR know the difference 'cept for spark timing.

Time to check the time! Take off the LH cover, note flywheel position at spark time, then measure the piston movement. The 'H' 200 is 21º or 2mm BTDC at 6KRPM.

It's a lot easier to check timing with points!!

[quote]Could it have something to do with pulling it through a compression stroke and it firing the piston back into the proper direction ? [quote] Yeah, that's my guess. Same thing happens when kicking, but you usually just get a 'backfire' not a full-on running motor...Crazy.

That's different, sez me.

Engine speed is slow when kicking. The spark being beforeTDC, if there is not enough inertia to keep the piston moving through TDC..after the spark, the piston is going to be fired backwards.

If the bike is moving backwards 'through' a compression stroke..the spark is going to push the piston down..in the same rotational direction it WAS moving. Backwards.

No matter how slow the piston moves with the bike moving backwards, the spark is going to happen AFTER TDC which will push the piston in the same direction it's going...not reverse it.

Pre-ignition or detonation would do it too. That would be independent of crankshaft rotation direction, subject simply to compression. That could get you an 'advanced' firing event regardless of spark timing.

For whatever reason, his ignition point is happening ATDC, which looks like BTDC when moving 'backwards', so the rotation reverses, just like the 'back kick' you get sometimes.

'Backwards' being used in regard to direction of motion of the BIKE. The piston, of course, doesn't move backwards...just up and down.

My model airplanes used to do the same thing. Only trouble was that I couldn't adjust the timing on a glow plug. I used to throw a rag on the prop to kill the engine, then one day she said she'd had enough and left me. Ah, the loneliness.