What causes the pullstart on a 4 stroke to pull back and rip out of your hand?

Its called a backfire. When you pull give it a good solid pull. Don't baby it. The slower you pull the more chance the plug will fire and spin the crank backwards just as the piston reaches top dead center. That's when it kicks and jerks the heck out of your hand. You need the momentum of a good pull to keep the crank spinning in the right direction.
Tom
 
A friend had one of the good ol' big cc dirt bikes back in the 70's and it backfired once while he was kick starting it. His right leg was in a cast for most of that summer and the bike got sold.
 
Yea, those XT500 Yamahas, had a little window to see the Cam, if I kicked it without getting the mark in the window, BAM!, tore me shoe off several times. I think Tom is dead on here, I would get the backfire when I was "afraid" to give it heck.
 
Mac said:
Yea, those XT500 Yamahas, had a little window to see the Cam, if I kicked it without getting the mark in the window, BAM!, tore me shoe off several times. I think Tom is dead on here, I would get the backfire when I was "afraid" to give it heck.
Click to expand...

I have a '79 XT500 in my garage. It has sent me over the bars twice from kick back, even though I lined up the white mark in the window.
 
Also, a backfire isn't restricted to 4 stroke engines. Try flipping the prop of a 2 stroke model airplane engine with your fingers, doesn't matter the size, you can get hurt when the little bugger backfires. The bigger the propeller, the more it hurts :(
Tom
 
Remember the little starter springs o .049 engines? More then once the prop slipped out of my fingers while winding it backwards. lol

Dad used a chunk of heavy rubber garden hose to start anything bigger then a .25 and from the number of cuts in the hose he would have lost his finger several times over.
 
I went to an electric starter when I graduated from .019 to a .40. One backfire, one chopped up finger and I never flipped another prop. When I got into giant scale and started running those monster 4 strokes I had to get a bigger battery to spin those puppies. You DO NOT want to hand prop one of those.
I had a friend with a 1/4 scale P-51 that got away from him while starting the engine. We called 911 and he was airlifted to the hospital with wounds that looked like Jaws got him. Inner thigh, calf and the top of one foot. Over three hundred stitches to put him back together.
And you thought they were just toy airplanes.
Tom
 
My piper with Enya .80 4 st. cut my hand (down from the thumb), took 3 CHUNKs out, almost hospital time, I was starting it, no backfire, pulling the glow ignitor off, right thru the prop, couldn't feel anything for a week, then I wish I couldn't feel it, I went and bought a remote glow adapter... I was down at Earnie Hubbards Helo school(R/C), in Fla. a guy with a hotrod .60 helo flew into himself from a hover, thigh slices to the bone, life flight evac, he made it but what a bloodbath! Hey, I think we hijacked this thread???
 
Our apologizes to the OP. Sorry guy. When old R/Cers get to telling war stories, ya can't shut 'em up.
At least I hope we answered his question.
Tom
 
the nitro rc engines generally only kick back when they are flooded, but the high performance 4 stroke bike engines kick back from lots of timing advance. the big cc 2 strokes do that too
 
Just a quick comment concerning the rope starter on the 4-stroke motor. I find it best to gently pull the rope until the motor passes the compression stroke. Next I gently pull the rope and the motor easily leaps to life. If the rope starter is pulled too hard and out the the end of the rope it can damage the PLASTIC parts inside.

I have both Honda & HS motors and I find the Honda is far worse to "Kick back".

Don't want to hijack this thread, but I learned this trick on my 450 Ducati single during my racing days. The piston in the Ducati was 86 MM, and required a lot of gusto to get it in motion.


Have fun,
 
On my Suburu and HF engines I pull rope out until the engine comes up on compression and then giive it a sharp pull and let the rope retract gently. They start every time. You can't get too violent with the rope starter because they are some what fragle.
Some of you oldtimers can remember hand cranking the old farm tractor or the 1929 Model A. You had to make sure it was out of gear and the mechanical spark advance was retarded about 2 notches. grab the hand crank with 4 fingers never put your thumb over the bar;. If that engine ever kicked back you're loolking at a broken arm. Many old farmers with their right arem in a sling because they didnt' do it rignt.
Some diesel marine 2 cyclle engines you had to start with a crow bar. I'll let you young whippersnappers figure that one out. LOL
Old buzzard
 
Compression coupled with a spark just prior to TDC will yank that rope right out of your hand !! I do the same as Buzzard. Simply pull easy until you feel the compression stroke coming.. Once felt, stop.. Then retract or let the rope all the way in or back down, and then give her a good firm pull, and she starts easy. Employing this method allows you to get a run up to the next compression stroke. Some flywheel action. IF you think you have an arm ripper with this little 4 stroke, try rope starting a single cylinder Diesel rope start!!! On the Diesel, once you find compression, you hand wind the motor all the way back as far from compression as you can, wind on the rope.. And get a run going at compression !! Look out !!
 
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